MyBatis 的在使用上的留意事项及其辨析

1. MyBatis 的在使用上的留意事项及其辨析

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目录

• 1. MyBatis 的在使用上的留意事项及其辨析
  
• 2. 准备工作
  
• 3. #{ } 与 ${ } 的区别和使用
  
• {}
  
  
  
  • 3.1 什么情况下必须使用 $
    
    
    
    • 3.1.1 拼接表名
      
    • 3.1.2 批量删除
      
    • 3.1.3 模糊查询
      
      
      
      • 3.1.3.1 使用 ${ }的方式
        
      • 3.1.3.2 使用 #{ } 的方式
        
      
      
    
    
  
  
• 4. typeAliases 别名定义的使用
  
  
  
  • 4.1 typeAliases 的第一种方式：typeAlias
    
  • 4.2 typeAliases 的第二种方式：package
    
  
  
• 5. mappers 路径设置的使用
  
  
  
  • 5.1 mapper 标签下的 resource 属性的使用
    
  • 5.2 mapper 标签下的 url 属性的使用
    
  • 5.3 mapper 标签下的 class 属性的使用
    
  • 5.4 package 标签的使用
    
  
  
• 6. 在 IDEA 中自定义配置文件模板
  
• 7. 补充：插入数据时获取自动天生的主键的值
  
• 8. 总结：
  
• { } 与 ${ } 的区别和使用
  
• 9. 最后：
  

2. 准备工作

数据表结构的计划，数据表名为：t_car

t_car 表中的数据信息：

在pom.xml 文件当中配置相关的依赖的 jar 包如下：

1. <?xml version="1.0" encoding="UTF-8"?>
2. <project xmlns="http://maven.apache.org/POM/4.0.0"
3. <mappers>
4.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
5.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
6.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
7. </mappers>   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
8. <mappers>
9.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
10.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
11.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
12. </mappers>   xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
13.     <modelVersion>4.0.0</modelVersion>
15.     <groupId>com.rainbowsea</groupId>
16.     <artifactId>mybatis-005-crud-blog</artifactId>
17.     <version>1.0-SNAPSHOT</version>
19.     <properties>
20. <mappers>
21.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
22.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
23.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
24. </mappers>  <maven.compiler.source>17</maven.compiler.source>
25. <mappers>
26.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
27.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
28.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
29. </mappers>  <maven.compiler.target>17</maven.compiler.target>
30.     </properties>
32.     <dependencies>
33. <mappers>
34.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
35.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
36.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
37. </mappers>  
38. <mappers>
39.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
40.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
41.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
42. </mappers>  <dependency>
43. <mappers>
44.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
45.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
46.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
47. </mappers><mappers>
48.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
49.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
50.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
51. </mappers><groupId>org.mybatis</groupId>
52. <mappers>
53.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
54.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
55.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
56. </mappers><mappers>
57.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
58.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
59.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
60. </mappers><artifactId>mybatis</artifactId>
61. <mappers>
62.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
63.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
64.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
65. </mappers><mappers>
66.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
67.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
68.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
69. </mappers><version>3.5.10</version>
70. <mappers>
71.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
72.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
73.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
74. </mappers>  </dependency>
76. <mappers>
77.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
78.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
79.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
80. </mappers>  
81. <mappers>
82.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
83.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
84.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
85. </mappers>  <dependency>
86. <mappers>
87.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
88.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
89.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
90. </mappers><mappers>
91.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
92.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
93.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
94. </mappers><groupId>mysql</groupId>
95. <mappers>
96.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
97.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
98.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
99. </mappers><mappers>
100.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
101.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
102.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
103. </mappers><artifactId>mysql-connector-java</artifactId>
104. <mappers>
105.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
106.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
107.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
108. </mappers><mappers>
109.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
110.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
111.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
112. </mappers><version>8.0.30</version>
113. <mappers>
114.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
115.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
116.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
117. </mappers>  </dependency>
119. <mappers>
120.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
121.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
122.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
123. </mappers>  <dependency>
124. <mappers>
125.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
126.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
127.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
128. </mappers><mappers>
129.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
130.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
131.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
132. </mappers><groupId>junit</groupId>
133. <mappers>
134.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
135.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
136.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
137. </mappers><mappers>
138.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
139.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
140.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
141. </mappers><artifactId>junit</artifactId>
142. <mappers>
143.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
144.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
145.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
146. </mappers><mappers>
147.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
148.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
149.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
150. </mappers><version>4.13.2</version>
151. <mappers>
152.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
153.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
154.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
155. </mappers><mappers>
156.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
157.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
158.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
159. </mappers><scope>test</scope>
160. <mappers>
161.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
162.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
163.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
164. </mappers>  </dependency>
166. <mappers>
167.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
168.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
169.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
170. </mappers>  
171. <mappers>
172.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
173.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
174.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
175. </mappers>  <dependency>
176. <mappers>
177.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
178.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
179.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
180. </mappers><mappers>
181.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
182.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
183.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
184. </mappers><groupId>ch.qos.logback</groupId>
185. <mappers>
186.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
187.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
188.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
189. </mappers><mappers>
190.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
191.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
192.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
193. </mappers><artifactId>logback-classic</artifactId>
194. <mappers>
195.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
196.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
197.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
198. </mappers><mappers>
199.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
200.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
201.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
202. </mappers><version>1.2.11</version>
203. <mappers>
204.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
205.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
206.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
207. </mappers>  </dependency>
208.     </dependencies>
210. </project>

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配置 logback 的配置文件，用于打印显示，我们的日记信息，方便我们查看我们的运行过程，效果。

1. <?xml version="1.0" encoding="UTF-8"?>
3. <configuration debug="false">
4.    
5.     <appender name="STDOUT" >
6. <mappers>
7.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
8.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
9.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
10. </mappers>  <encoder >
11. <mappers>
12.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
13.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
14.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
15. </mappers><mappers>
16.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
17.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
18.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
19. </mappers>
20. <mappers>
21.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
22.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
23.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
24. </mappers><mappers>
25.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
26.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
27.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
28. </mappers><pattern>%d{yyyy-MM-dd HH:mm:ss.SSS} [%thread] %-5level %logger{50} - %msg%n</pattern>
29. <mappers>
30.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
31.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
32.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
33. </mappers>  </encoder>
34.     </appender>
36.    
37.     <logger name="com.apache.ibatis" level="TRACE"/>
38.     <logger name="java.sql.Connection" level="DEBUG"/>
39.     <logger name="java.sql.Statement" level="DEBUG"/>
40.     <logger name="java.sql.PreparedStatement" level="DEBUG"/>
42.    
43.     <root level="DEBUG">
44. <mappers>
45.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
46.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
47.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
48. </mappers>  <appender-ref ref="STDOUT"/>
49. <mappers>
50.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
51.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
52.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
53. </mappers>  <appender-ref ref="FILE"/>
54.     </root>
56. </configuration>

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配置 MyBatis 的核心配置文件，

1. <?xml version="1.0" encoding="UTF-8" ?>
2. <!DOCTYPE configuration
3. <mappers>
4.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
5.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
6.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
7. </mappers>  PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
8. <mappers>
9.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
10.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
11.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
12. </mappers>  "http://mybatis.org/dtd/mybatis-3-config.dtd">
13. <configuration>
14.    
15.     <typeAliases>
16. <mappers>
17.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
18.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
19.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
20. </mappers>  
21. <mappers>
22.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
23.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
24.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
25. </mappers>  <package name="com.rainbowsea.mybatis.pojo"/>
26.     </typeAliases>
27.     <environments default="mybatis">
29. <mappers>
30.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
31.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
32.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
33. </mappers>  <environment id="mybatis">
34. <mappers>
35.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
36.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
37.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
38. </mappers><mappers>
39.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
40.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
41.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
42. </mappers>
43. <mappers>
44.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
45.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
46.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
47. </mappers><mappers>
48.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
49.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
50.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
51. </mappers><transactionManager type="JDBC"/>
52. <mappers>
53.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
54.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
55.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
56. </mappers><mappers>
57.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
58.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
59.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
60. </mappers><dataSource type="POOLED">
61. <mappers>
62.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
63.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
64.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
65. </mappers><mappers>
66.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
67.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
68.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
69. </mappers>    <property name="driver" value="com.mysql.cj.jdbc.Driver"/>
70. <mappers>
71.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
72.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
73.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
74. </mappers><mappers>
75.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
76.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
77.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
78. </mappers>    <property name="url" value="jdbc:mysql://localhost:3306/mybatis"/>
79. <mappers>
80.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
81.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
82.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
83. </mappers><mappers>
84.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
85.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
86.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
87. </mappers>    <property name="username" value="root"/>
88. <mappers>
89.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
90.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
91.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
92. </mappers><mappers>
93.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
94.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
95.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
96. </mappers>    <property name="password" value="MySQL123"/>
97. <mappers>
98.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
99.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
100.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
101. </mappers><mappers>
102.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
103.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
104.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
105. </mappers></dataSource>
106. <mappers>
107.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
108.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
109.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
110. </mappers>  </environment>
111.     </environments>
112.     <mappers>
113. <mappers>
114.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
115.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
116.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
117. </mappers>  
118. <mappers>
119.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
120.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
121.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
122. </mappers>  <mapper resource="CarMapper.xml"></mapper>
123.     </mappers>
124. </configuration>

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对照 t_car 创建的ORM 映射的 Car 类
留意：在MyBatis 当中对应的ORM ，一般在框架里对应的 Bean实体类，一定要实现该 set 和 get 方法以及无参数构造方法，无法框架无法使用反射机制，进行操纵 。
发起用包装类，如许可以防止 Null的问题，因为（简单类型 int num = null ，是不可以赋值为 null）的编译无法通过

1. package com.rainbowsea.mybatis.pojo;
3. public class Car {
4.     // 数据库表当中的字段应该和pojo类的属性一一对应
5.     // 建议使用包装类，这样可以防止null的问题
6.     private Long id;
7.     private String carNum;
8.     private String brand;
9.     private Double guidePrice;
10.     private String produceTime;
11.     private String carType;
13.     public Car() {
14.     }
16.     public Car(Long id, String carNum, String brand, Double guidePrice, String produceTime, String carType) {
17. <mappers>
18.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
19.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
20.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
21. </mappers>  this.id = id;
22. <mappers>
23.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
24.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
25.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
26. </mappers>  this.carNum = carNum;
27. <mappers>
28.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
29.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
30.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
31. </mappers>  this.brand = brand;
32. <mappers>
33.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
34.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
35.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
36. </mappers>  this.guidePrice = guidePrice;
37. <mappers>
38.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
39.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
40.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
41. </mappers>  this.produceTime = produceTime;
42. <mappers>
43.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
44.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
45.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
46. </mappers>  this.carType = carType;
47.     }
49.     @Override
50.     public String toString() {
51. <mappers>
52.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
53.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
54.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
55. </mappers>  return "Car{" +
56. <mappers>
57.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
58.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
59.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
60. </mappers><mappers>
61.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
62.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
63.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
64. </mappers>    "id=" + id +
65. <mappers>
66.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
67.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
68.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
69. </mappers><mappers>
70.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
71.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
72.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
73. </mappers>    ", carNum='" + carNum + '\'' +
74. <mappers>
75.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
76.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
77.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
78. </mappers><mappers>
79.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
80.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
81.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
82. </mappers>    ", brand='" + brand + '\'' +
83. <mappers>
84.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
85.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
86.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
87. </mappers><mappers>
88.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
89.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
90.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
91. </mappers>    ", guidePrice=" + guidePrice +
92. <mappers>
93.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
94.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
95.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
96. </mappers><mappers>
97.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
98.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
99.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
100. </mappers>    ", produceTime='" + produceTime + '\'' +
101. <mappers>
102.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
103.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
104.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
105. </mappers><mappers>
106.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
107.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
108.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
109. </mappers>    ", catType='" + carType + '\'' +
110. <mappers>
111.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
112.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
113.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
114. </mappers><mappers>
115.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
116.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
117.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
118. </mappers>    '}';
119.     }
121.     public Long getId() {
122. <mappers>
123.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
124.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
125.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
126. </mappers>  return id;
127.     }
129.     public void setId(Long id) {
130. <mappers>
131.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
132.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
133.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
134. </mappers>  this.id = id;
135.     }
137.     public String getCarNum() {
138. <mappers>
139.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
140.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
141.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
142. </mappers>  return carNum;
143.     }
145.     public void setCarNum(String carNum) {
146. <mappers>
147.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
148.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
149.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
150. </mappers>  this.carNum = carNum;
151.     }
153.     public String getBrand() {
154. <mappers>
155.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
156.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
157.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
158. </mappers>  return brand;
159.     }
161.     public void setBrand(String brand) {
162. <mappers>
163.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
164.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
165.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
166. </mappers>  this.brand = brand;
167.     }
169.     public Double getGuidePrice() {
170. <mappers>
171.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
172.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
173.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
174. </mappers>  return guidePrice;
175.     }
177.     public void setGuidePrice(Double guidePrice) {
178. <mappers>
179.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
180.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
181.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
182. </mappers>  this.guidePrice = guidePrice;
183.     }
185.     public String getProduceTime() {
186. <mappers>
187.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
188.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
189.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
190. </mappers>  return produceTime;
191.     }
193.     public void setProduceTime(String produceTime) {
194. <mappers>
195.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
196.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
197.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
198. </mappers>  this.produceTime = produceTime;
199.     }
201.     public String getcarType() {
202. <mappers>
203.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
204.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
205.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
206. </mappers>  return carType;
207.     }
209.     public void setcarType(String catType) {
210. <mappers>
211.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
212.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
213.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
214. </mappers>  this.carType = catType;
215.     }
216. }

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对应操纵实现CRUD（增删改查）的接口(这里是：CarMapper接口)，在MyBtis 当中 ，关于 CRUD(增删改查)操纵的接口/实现类，都是 mapper 结尾的作为长期层，而在 MVC的三层架构中，则是以 dao 为后缀作为CRUD(增删改查)操纵的接口/实现类。

1. package com.rainbowsea.mybatis.mapper;
3. import com.rainbowsea.mybatis.pojo.Car;
5. import java.util.List;
7. public interface CarMapper {
10.     /**
11.      * 新增 Car
12.      * @param car
13.      * @return
14.      */
15.     int insert(Car car);
18.     /**
19.      * 根据id 删除 Car
20.      * @param id
21.      * @return
22.      */
23.     int deleteById(Long id);
26.     /**
27.      * 修改汽车信息
28.      * @param car
29.      * @return
30.      */
31.     int update(Car car);
34.     /**
35.      * 根据id查询汽车信息
36.      * @param id
37.      * @return
38.      */
39.     Car selectById(Long id);
42.     /**
43.      * 获取所有的汽车信息
44.      * @return
45.      */
46.     List<Car> selectAll();
47. }

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获取 Sqlsession 对象的工具类的编写。

1. package com.rainbowsea.mybatis.utils;
4. import org.apache.ibatis.io.Resources;
5. import org.apache.ibatis.session.SqlSession;
6. import org.apache.ibatis.session.SqlSessionFactory;
7. import org.apache.ibatis.session.SqlSessionFactoryBuilder;
9. import java.io.IOException;
11. public class SqlSessionUtil {
12.     // 工具类的构造方法一般都是私有话化的
13.     // 工具类中所有的方法都是静态的，直接类名即可调用，不需要 new 对象
14.     // 为了防止new对象，构造方法私有化。
16.     private SqlSessionUtil() {
18.     }
22.     private static SqlSessionFactory sessionFactory = null;
24.     // 静态代码块，类加载时执行
25.     // SqlSessionUtil 工具类在进行第一次加载的时候，解析mybatis-config.xml 文件，创建SqlSessionFactory对象。
26.     static {
27. <mappers>
28.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
29.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
30.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
31. </mappers>  // 获取到  SqlSessionFactoryBuilder 对象
32. <mappers>
33.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
34.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
35.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
36. </mappers>  SqlSessionFactoryBuilder sqlSessionFactoryBuilder = new SqlSessionFactoryBuilder();
38. <mappers>
39.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
40.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
41.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
42. </mappers>  // 获取到SqlSessionFactory 对象
43. <mappers>
44.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
45.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
46.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
47. </mappers>  // SQlsessionFactory对象，一个SqlSessionFactory对应一个 environment, 一个environment通常是一个数据库
48. <mappers>
49.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
50.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
51.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
52. </mappers>  try {
53. <mappers>
54.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
55.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
56.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
57. </mappers><mappers>
58.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
59.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
60.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
61. </mappers>sessionFactory = sqlSessionFactoryBuilder.build(Resources.getResourceAsStream("mybatis-config.xml"),
62. <mappers>
63.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
64.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
65.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
66. </mappers><mappers>
67.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
68.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
69.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
70. </mappers><mappers>
71.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
72.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
73.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
74. </mappers>  "mybatis");
75. <mappers>
76.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
77.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
78.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
79. </mappers>  } catch (IOException e) {
80. <mappers>
81.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
82.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
83.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
84. </mappers><mappers>
85.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
86.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
87.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
88. </mappers>throw new RuntimeException(e);
89. <mappers>
90.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
91.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
92.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
93. </mappers>  }
95.     }
97.     /**
98.      * 获取会话对象
99.      * @return SqlSession
100.      */
101.     public static SqlSession openSession() {
102. <mappers>
103.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
104.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
105.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
106. </mappers>  // 获取到 SqlSession 对象
107. <mappers>
108.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
109.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
110.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
111. </mappers>  SqlSession sqlSession = sessionFactory.openSession();
112. <mappers>
113.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
114.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
115.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
116. </mappers>  return sqlSession;
117.     }
118. }

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3. #{ } 与 ${ } 的区别和使用

• #{ } ：先编译 SQL 语句，再对占位符传值，底层是 PrepareedStatement 实现，可以防止 SQL 注入，比力常用
  
• ${ }：先进行SQL语句的拼接，然后再对SQL语句进行编译，底层是 Statement 实现，这种方式存在 SQL注入现象，SQL注入的风险，简单的说就是，直接将传入的值拼接为了SQL语句，然后再实行的）。只有在需要进行SQL语句关键字拼接的情况下才会用到。
  
• 简单的说一个区别就是：#{} 传的值是带有 '' 单引号的，而 ${} 传的值是（直接就是值，没有单引号，或者是双引号，两个都没有）
  

查验一下。
这里我们根据汽车的 car_type 查询，为新能源汽车的。多条记录
首先这里我们先使用 #{} ，传的是带有 '' 单引号的值 ——> '新能源'

1. package com.rainbowsea.mybatis.mapper;
3. import com.rainbowsea.mybatis.pojo.Car;
5. import java.util.List;
7. /**
8. * 封装汽车相关信息的pojo类，普通的Java类
9. */
10. public interface CarMapper {
12.     /**
13.      * 根据汽车类型获取汽车信息
14.      * @param carType
15.      * @return
16.      */
17.     List<Car> selectByCarType(String carType);
19. }

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1. <?xml version="1.0" encoding="UTF-8" ?>
2. <!DOCTYPE mapper
3. <mappers>
4.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
5.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
6.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
7. </mappers>  PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
8. <mappers>
9.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
10.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
11.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
12. </mappers>  "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
15. <mapper namespace="com.rainbowsea.mybatis.mapper.CarMapper">
17.    
18.    
19.     <select id="selectByCarType" resultType="com.rainbowsea.mybatis.pojo.Car">
20. <mappers>
21.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
22.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
23.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
24. </mappers>  select id,
25. <mappers>
26.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
27.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
28.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
29. </mappers><mappers>
30.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
31.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
32.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
33. </mappers>   car_num<mappers>
34.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
35.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
36.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
37. </mappers>as carNum,
38. <mappers>
39.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
40.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
41.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
42. </mappers><mappers>
43.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
44.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
45.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
46. </mappers>   brand,
47. <mappers>
48.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
49.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
50.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
51. </mappers><mappers>
52.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
53.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
54.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
55. </mappers>   guide_price  as guidePrice,
56. <mappers>
57.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
58.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
59.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
60. </mappers><mappers>
61.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
62.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
63.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
64. </mappers>   produce_time as produceTime,
65. <mappers>
66.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
67.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
68.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
69. </mappers><mappers>
70.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
71.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
72.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
73. </mappers>   car_type     as carType
74. <mappers>
75.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
76.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
77.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
78. </mappers>  from t_car
79. <mappers>
80.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
81.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
82.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
83. </mappers>  where car_type = #{carType}
84.     </select>
86. </mapper>

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运行Java步伐：

查询乐成。
下面我们再实行用  ${} ，直接就是新能源的值，没有单引号，也没有双引号，就是直接就是——》新能源的值。运行结果如下：

比力上述#{}和 ?{} 的运行结果：

{}

${}

通过实行可以清楚的看到，sql 语句中是带有 ? 的，这个 ? 就是各人在JDBC中所学的占位符，专门用来接收值的。
把“新能源”以 String 类型的值，传递给 ? ，加上 '' 单引号，作为字符串传入进行，实行SQL语句
这就是 #{}，它会先进行sql语句的预编译，然后再给占位符传值。
而 ${} 是直接将我们的 新能源 作为值，传入给SQL语句的，留意 ${} 的方式是不会加单引号/双引号的，而是作为值，直接拼接到 SQL语句当中去了，但是，在我们这个查询的SQL当中，新能源就是必须要为字符串才行的，不然是无法实行SQL语句，是无法识别出来的。

3.1 什么情况下必须使用 $

当需要进行 sql 语句关键字拼接的时候，简单的说就是当我们要使用 SQL语句当中的关键字的时候，以及要传的值，不要单引号/双引号的值的时候，就必须使用${ }
需求：通过向sql语句中注入asc或desc关键字，来完成数据的升序或降序排列。
根据数据表中的 produce_time日期时间进行排序。
因为这里我们使用到了 ASC / DESC 这两者都是 SQL语句当中的关键字，以是我们需要使用 ${} 的方式。

1. package com.rainbowsea.mybatis.mapper;
3. import com.rainbowsea.mybatis.pojo.Car;
5. import java.util.List;
7. /**
8. * 封装汽车相关信息的pojo类，普通的Java类
9. */
10. public interface CarMapper {
12.     /**
13.      * 查询所有的汽车信息，然后通过 asc 升序，desc 降序
14.      * @param ascOrDesc
15.      * @return
16.      */
17.     List<Car> selectAllByAscOrDesc(String ascOrDesc);
20. }

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1. <?xml version="1.0" encoding="UTF-8" ?>
2. <!DOCTYPE mapper
3. <mappers>
4.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
5.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
6.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
7. </mappers>  PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
8. <mappers>
9.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
10.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
11.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
12. </mappers>  "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
15. <mapper namespace="com.rainbowsea.mybatis.mapper.CarMapper">
17.    
18.    
19.     <select id="selectAllByAscOrDesc" resultType="com.rainbowsea.mybatis.pojo.Car">
20. <mappers>
21.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
22.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
23.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
24. </mappers>  select id,
25. <mappers>
26.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
27.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
28.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
29. </mappers><mappers>
30.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
31.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
32.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
33. </mappers>   car_num<mappers>
34.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
35.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
36.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
37. </mappers>as carNum,
38. <mappers>
39.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
40.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
41.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
42. </mappers><mappers>
43.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
44.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
45.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
46. </mappers>   brand,
47. <mappers>
48.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
49.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
50.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
51. </mappers><mappers>
52.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
53.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
54.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
55. </mappers>   guide_price  as guidePrice,
56. <mappers>
57.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
58.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
59.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
60. </mappers><mappers>
61.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
62.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
63.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
64. </mappers>   produce_time as produceTime,
65. <mappers>
66.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
67.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
68.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
69. </mappers><mappers>
70.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
71.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
72.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
73. </mappers>   car_type     as carType
74. <mappers>
75.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
76.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
77.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
78. </mappers>  from t_car
79. <mappers>
80.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
81.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
82.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
83. </mappers>  order by produce_time ${ascOrDesc}
84.     </select>
86. </mapper>

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Java步伐运行测试：

1. public class TestCarMapper {
3.     @Test
4.     public void testSelectAllByAscOrDesc() {
5. <mappers>
6.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
7.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
8.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
9. </mappers>  SqlSession sqlSession = SqlSessionUtil.openSession();
10. <mappers>
11.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
12.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
13.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
14. </mappers>  CarMapper mapper = sqlSession.getMapper(CarMapper.class);
15. <mappers>
16.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
17.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
18.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
19. </mappers>  List<Car> cars = mapper.selectAllByAscOrDesc("asc");
20. <mappers>
21.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
22.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
23.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
24. </mappers>  cars.forEach(car -> {
25. <mappers>
26.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
27.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
28.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
29. </mappers><mappers>
30.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
31.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
32.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
33. </mappers>System.out.println(car);
34. <mappers>
35.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
36.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
37.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
38. </mappers>  });
40. <mappers>
41.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
42.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
43.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
44. </mappers>  sqlSession.close();
45.     }
47. }

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如果换成 #{} ，将SQL 语句的关键字 asc 作为字符串的形式拼接到 SQL语句当中是会编译失败的了。

3.1.1 拼接表名

业务背景：实际开发中，有的表数据量非常庞大，大概会接纳分表方式进行存储，比如每天天生一张表，表的名字与日期挂钩，例如：2022年8月1日天生的表：t_user20220108。2000年1月1日天生的表：t_user20000101。此时前端在进行查询的时候会提交一个具体的日期，比如前端提交的日期为：2000年1月1日，那么后端就会根据这个日期动态拼接表名为：t_user20000101。有了这个表名之后，将表名拼接到sql语句当中，返回查询结果。那么各人思考一下，拼接表名到sql语句当中应该使用#{} 还是 ${} 呢？
使用#{}会是如许：select * from 't_car'
使用${}会是如许：select * from t_car
向SQL语句当中拼接表名，就需要使用${}
实际业务当中，大概存在分表存储的数据的情况，因为一张表存的话，数据量太大了，查询效率比力低。
可以将这些数据有规律的分表存储，如许在查询的时候效率就比力高，因为扫描的数据量变小了
日记表，专门存储日记信息，如果t_long 只有一张表，这张表中每一天都会产生许多的log,逐步的，这个表中数据会许多，
怎么办理呢
可以每天天生一个新表，每张表以当天日期作为名称，例如：
t_log_202209801
t_log_20220902
你想知道某一天的日记信息怎么办呢？
假设本日20220901，那么直接查：t_log-20220901的表即可。
下面是我们的t_log_20220902 的数据表信息

对应数据表的 POJO 类计划：

1. package com.rainbowsea.mybatis.pojo;
4. public class Log {
5.     private Integer id;
6.     private String log;
7.     private String time;
9.     public Log() {
10.     }
13.     public Log(Integer id, String log, String time) {
14. <mappers>
15.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
16.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
17.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
18. </mappers>  this.id = id;
19. <mappers>
20.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
21.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
22.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
23. </mappers>  this.log = log;
24. <mappers>
25.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
26.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
27.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
28. </mappers>  this.time = time;
29.     }
32.     @Override
33.     public String toString() {
34. <mappers>
35.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
36.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
37.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
38. </mappers>  return "Log{" +
39. <mappers>
40.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
41.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
42.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
43. </mappers><mappers>
44.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
45.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
46.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
47. </mappers>    "id=" + id +
48. <mappers>
49.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
50.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
51.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
52. </mappers><mappers>
53.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
54.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
55.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
56. </mappers>    ", log='" + log + '\'' +
57. <mappers>
58.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
59.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
60.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
61. </mappers><mappers>
62.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
63.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
64.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
65. </mappers>    ", time='" + time + '\'' +
66. <mappers>
67.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
68.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
69.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
70. </mappers><mappers>
71.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
72.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
73.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
74. </mappers>    '}';
75.     }
78.     public Integer getId() {
79. <mappers>
80.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
81.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
82.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
83. </mappers>  return id;
84.     }
86.     public void setId(Integer id) {
87. <mappers>
88.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
89.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
90.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
91. </mappers>  this.id = id;
92.     }
94.     public String getLog() {
95. <mappers>
96.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
97.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
98.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
99. </mappers>  return log;
100.     }
102.     public void setLog(String log) {
103. <mappers>
104.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
105.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
106.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
107. </mappers>  this.log = log;
108.     }
110.     public String getTime() {
111. <mappers>
112.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
113.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
114.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
115. </mappers>  return time;
116.     }
118.     public void setTime(String time) {
119. <mappers>
120.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
121.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
122.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
123. </mappers>  this.time = time;
124.     }
125. }

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对应的LogMapper 的接口信息编写。
首先我们使用 ${} 的方式测试运行。

1. package com.rainbowsea.mybatis.mapper;
4. import com.rainbowsea.mybatis.pojo.Log;
6. import java.util.List;
8. public interface LogMapper {
10.     /**
11.      * 根据日期查询不同的表，获取表中所有的日志
12.      *
13.      * @param date
14.      * @return
15.      */
16.     List<Log> selectAllByTable(String date);
17. }

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1. <?xml version="1.0" encoding="UTF-8" ?>
2. <!DOCTYPE mapper
3. <mappers>
4.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
5.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
6.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
7. </mappers>  PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
8. <mappers>
9.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
10.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
11.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
12. </mappers>  "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
15. <mapper namespace="com.rainbowsea.mybatis.mapper.LogMapper">
17.    
18.    
19.     <select id="selectAllByTable" resultType="com.rainbowsea.mybatis.pojo.Log">
20. <mappers>
21.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
22.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
23.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
24. </mappers>  select * from t_log_${date};
25.     </select>
27. </mapper>

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1. package com.rainbowsea.test;
3. import com.rainbowsea.mybatis.mapper.LogMapper;
4. import com.rainbowsea.mybatis.pojo.Log;
5. import com.rainbowsea.mybatis.utils.SqlSessionUtil;
6. import org.apache.ibatis.session.SqlSession;
7. import org.junit.Test;
9. import java.util.List;
11. public class LogMapperTest {
13.     @Test
14.     public void testSelectAllByTable() {
15. <mappers>
16.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
17.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
18.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
19. </mappers>  SqlSession sqlSession = SqlSessionUtil.openSession();
20. <mappers>
21.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
22.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
23.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
24. </mappers>  LogMapper mapper = sqlSession.getMapper(LogMapper.class);
25. <mappers>
26.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
27.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
28.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
29. </mappers>  List<Log> logs = mapper.selectAllByTable("20220902");
30. <mappers>
31.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
32.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
33.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
34. </mappers>  logs.forEach(log -> {
35. <mappers>
36.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
37.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
38.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
39. </mappers><mappers>
40.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
41.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
42.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
43. </mappers>System.out.println(log);
44. <mappers>
45.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
46.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
47.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
48. </mappers>  });
49.     }
50. }

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使用 ${} 拼接上的结果为：select * from t_log_20220902; 直接就是 20220902 的值，没有加单引号/双引号。

使用 #{ } 的方式是会带上 ‘’ 单引号的。

使用 #{} 拼接上的结果为：select * from t_log_‘20220902’; 加上的单引号后拼接上去，t_log_20220902是一个数据表名的，加了单引号后，MySQL 就找不到该数据表了，编译无法通过了。

3.1.2 批量删除

业务背景：一次删除多条记录。

批量删除：一次删除多条记录
批量删除的SQL语句有两种写法：

1. 第一种：or: delete form t_car where id =1 or id = 2 or id = 3
2. 第二种：delete from t_car where id in(1,2,3)

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假设如今使用in的方式处置惩罚，前端传过来的字符串：1, 2, 3
如果使用mybatis处置惩罚，应该使用#{} 还是 ${}
使用#{} ：delete from t_user where id in('1,2,3')  会加上单引号， 实行错误：1292 - Truncated incorrect DOUBLE value: '1,2,3'
使用${} ：delete from t_user where id in(1, 2, 3)，实行乐成

以是我们要接纳 ${} ，不加单引号的形式。

1. package com.rainbowsea.mybatis.mapper;
3. import com.rainbowsea.mybatis.pojo.Car;
5. import java.util.List;
7. /**
8. * 封装汽车相关信息的pojo类，普通的Java类
9. */
10. public interface CarMapper {
12.     /**
13.      * 批量删除，根据id
14.      * @param ids
15.      * @return
16.      */
17.     int deleteBath(String ids);
18. }

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1. <?xml version="1.0" encoding="UTF-8" ?>
2. <!DOCTYPE mapper
3. <mappers>
4.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
5.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
6.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
7. </mappers>  PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
8. <mappers>
9.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
10.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
11.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
12. </mappers>  "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
15. <mapper namespace="com.rainbowsea.mybatis.mapper.CarMapper">
17.    
18.     <delete id="deleteBath">
19. <mappers>
20.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
21.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
22.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
23. </mappers>  delete from t_car where id in(${ids})
24.     </delete>
26. </mapper>

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Java步伐测试，
留意因为我们这里是对数据表进行的修改操纵的，以是需要提交一下数据给数据库。
这里我们删除 id为(121，122，123) 三条记录。

1. package com.rainbowsea.test;
3. import com.rainbowsea.mybatis.mapper.CarMapper;
4. import com.rainbowsea.mybatis.pojo.Car;
5. import com.rainbowsea.mybatis.utils.SqlSessionUtil;
6. import org.apache.ibatis.session.SqlSession;
7. import org.junit.Test;
9. import java.util.List;
11. public class TestCarMapper {
13.     @Test
14.     public void testDeleteBath() {
15. <mappers>
16.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
17.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
18.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
19. </mappers>  SqlSession sqlSession = SqlSessionUtil.openSession();
20. <mappers>
21.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
22.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
23.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
24. </mappers>  CarMapper mapper = sqlSession.getMapper(CarMapper.class);
25. <mappers>
26.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
27.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
28.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
29. </mappers>  int count = mapper.deleteBath("121,122,123");
30. <mappers>
31.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
32.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
33.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
34. </mappers>  sqlSession.commit();
35. <mappers>
36.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
37.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
38.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
39. </mappers>  sqlSession.close();
41.     }
43. }

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如果使用 #{} 是将 使用#{} ：delete from t_user where id in('121,122,123')  会加上单引号， 实行错误：1292 - Truncated incorrect DOUBLE value: '121,122,123'

3.1.3 模糊查询

需求：查询小米系列的汽车。【只要品牌brand中含有小米两个字的都查询出来。】
关于模糊查询有四种方案：

• 方案一：'%${brand}%'
  
• 方案二: concat('%','${brand}','%')
  
• 方案三: count函数，这个是mysql数据库当中的一个函数，专门进行字符串拼接的  concat('%',#{brand},'%')
  
• 方案四: "%"#{brand}"%", 这种方式比力常用，也避免了SQL注入的问题。
  

1. 方案一：'%${brand}%'
2. 方案二: concat('%','${brand}','%')
3. 方案三: count函数，这个是mysql数据库当中的一个函数，专门进行字符串拼接的
4. <mappers>
5.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
6.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
7.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
8. </mappers>  concat('%',#{brand},'%')
9. 方案四: "%"#{brand}"%"

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四种方式：总的来说，都是为了拼接成字符串，把不是字符串的想办法拼接成字符串 。
3.1.3.1 使用 ${ }的方式

方案一：'%${brand}%'

1. package com.rainbowsea.mybatis.mapper;
3. import com.rainbowsea.mybatis.pojo.Car;
5. import java.util.List;
7. /**
8. * 封装汽车相关信息的pojo类，普通的Java类
9. */
10. public interface CarMapper {
15.     /**
16.      * 根据汽车品牌进行模糊查询
17.      * @param brand
18.      * @return
19.      */
20.     List<Car> selectByBrandLike(String brand);
24. }

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1. <?xml version="1.0" encoding="UTF-8" ?>
2. <!DOCTYPE mapper
3. <mappers>
4.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
5.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
6.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
7. </mappers>  PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
8. <mappers>
9.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
10.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
11.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
12. </mappers>  "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
15. <mapper namespace="com.rainbowsea.mybatis.mapper.CarMapper">
16.    
17.    
18.     <select id="selectByBrandLike" resultType="com.rainbowsea.mybatis.pojo.Car">
19. <mappers>
20.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
21.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
22.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
23. </mappers>  select
24. <mappers>
25.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
26.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
27.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
28. </mappers><mappers>
29.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
30.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
31.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
32. </mappers>id,
33. <mappers>
34.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
35.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
36.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
37. </mappers><mappers>
38.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
39.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
40.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
41. </mappers>car_num as carNum,
42. <mappers>
43.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
44.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
45.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
46. </mappers><mappers>
47.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
48.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
49.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
50. </mappers>brand,
51. <mappers>
52.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
53.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
54.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
55. </mappers><mappers>
56.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
57.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
58.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
59. </mappers>guide_price as guidePrice,
60. <mappers>
61.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
62.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
63.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
64. </mappers><mappers>
65.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
66.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
67.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
68. </mappers>produce_time as produceTime,
69. <mappers>
70.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
71.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
72.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
73. </mappers><mappers>
74.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
75.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
76.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
77. </mappers>car_type as carType
78. <mappers>
79.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
80.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
81.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
82. </mappers>  from t_car
83. <mappers>
84.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
85.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
86.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
87. </mappers>  where brand like '%${brand}%'
88.     </select>
90. </mapper>

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Java步伐运行结果：

方案二: concat('%','${brand}','%')

1. <?xml version="1.0" encoding="UTF-8" ?>
2. <!DOCTYPE mapper
3. <mappers>
4.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
5.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
6.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
7. </mappers>  PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
8. <mappers>
9.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
10.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
11.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
12. </mappers>  "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
15. <mapper namespace="com.rainbowsea.mybatis.mapper.CarMapper">
16.    
17.    
18.     <select id="selectByBrandLike" resultType="com.rainbowsea.mybatis.pojo.Car">
19. <mappers>
20.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
21.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
22.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
23. </mappers>  select
24. <mappers>
25.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
26.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
27.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
28. </mappers><mappers>
29.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
30.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
31.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
32. </mappers>id,
33. <mappers>
34.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
35.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
36.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
37. </mappers><mappers>
38.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
39.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
40.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
41. </mappers>car_num as carNum,
42. <mappers>
43.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
44.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
45.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
46. </mappers><mappers>
47.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
48.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
49.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
50. </mappers>brand,
51. <mappers>
52.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
53.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
54.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
55. </mappers><mappers>
56.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
57.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
58.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
59. </mappers>guide_price as guidePrice,
60. <mappers>
61.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
62.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
63.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
64. </mappers><mappers>
65.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
66.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
67.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
68. </mappers>produce_time as produceTime,
69. <mappers>
70.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
71.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
72.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
73. </mappers><mappers>
74.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
75.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
76.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
77. </mappers>car_type as carType
78. <mappers>
79.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
80.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
81.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
82. </mappers>  from t_car
83. <mappers>
84.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
85.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
86.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
87. </mappers>  where brand like concat('%','${brand}','%')
88.     </select>
89. </mapper>

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3.1.3.2 使用 #{ } 的方式

方案三： count函数，这个是mysql数据库当中的一个函数，专门进行字符串拼接的 concat('%',#{brand},'%')

1. <?xml version="1.0" encoding="UTF-8" ?>
2. <!DOCTYPE mapper
3. <mappers>
4.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
5.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
6.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
7. </mappers>  PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
8. <mappers>
9.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
10.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
11.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
12. </mappers>  "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
15. <mapper namespace="com.rainbowsea.mybatis.mapper.CarMapper">
16.    
17.    
18.     <select id="selectByBrandLike" resultType="com.rainbowsea.mybatis.pojo.Car">
19. <mappers>
20.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
21.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
22.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
23. </mappers>  select
24. <mappers>
25.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
26.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
27.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
28. </mappers><mappers>
29.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
30.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
31.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
32. </mappers>id,
33. <mappers>
34.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
35.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
36.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
37. </mappers><mappers>
38.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
39.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
40.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
41. </mappers>car_num as carNum,
42. <mappers>
43.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
44.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
45.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
46. </mappers><mappers>
47.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
48.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
49.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
50. </mappers>brand,
51. <mappers>
52.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
53.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
54.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
55. </mappers><mappers>
56.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
57.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
58.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
59. </mappers>guide_price as guidePrice,
60. <mappers>
61.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
62.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
63.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
64. </mappers><mappers>
65.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
66.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
67.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
68. </mappers>produce_time as produceTime,
69. <mappers>
70.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
71.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
72.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
73. </mappers><mappers>
74.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
75.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
76.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
77. </mappers>car_type as carType
78. <mappers>
79.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
80.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
81.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
82. </mappers>  from t_car
83. <mappers>
84.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
85.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
86.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
87. </mappers>  where brand like concat('%',#{brand},'%')
88.     </select>
89. </mapper>

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方案四:  "%"#{brand}"%", 这种方式比力常用，也避免了SQL注入的问题。

1. <?xml version="1.0" encoding="UTF-8" ?>
2. <!DOCTYPE mapper
3. <mappers>
4.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
5.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
6.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
7. </mappers>  PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
8. <mappers>
9.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
10.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
11.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
12. </mappers>  "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
15. <mapper namespace="com.rainbowsea.mybatis.mapper.CarMapper">
16.    
17.    
18.     <select id="selectByBrandLike" resultType="com.rainbowsea.mybatis.pojo.Car">
19. <mappers>
20.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
21.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
22.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
23. </mappers>  select
24. <mappers>
25.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
26.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
27.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
28. </mappers><mappers>
29.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
30.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
31.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
32. </mappers>id,
33. <mappers>
34.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
35.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
36.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
37. </mappers><mappers>
38.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
39.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
40.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
41. </mappers>car_num as carNum,
42. <mappers>
43.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
44.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
45.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
46. </mappers><mappers>
47.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
48.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
49.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
50. </mappers>brand,
51. <mappers>
52.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
53.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
54.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
55. </mappers><mappers>
56.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
57.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
58.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
59. </mappers>guide_price as guidePrice,
60. <mappers>
61.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
62.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
63.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
64. </mappers><mappers>
65.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
66.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
67.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
68. </mappers>produce_time as produceTime,
69. <mappers>
70.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
71.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
72.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
73. </mappers><mappers>
74.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
75.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
76.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
77. </mappers>car_type as carType
78. <mappers>
79.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
80.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
81.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
82. </mappers>  from t_car
83. <mappers>
84.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
85.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
86.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
87. </mappers>  where brand like "%"#{brand}"%"
88.     </select>
89. </mapper>

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测试运行：

4. typeAliases 别名定义的使用

我们来观察一下CarMapper.xml中的配置信息：

resultType 属性用来指定查询结果集的封装类型，这个名字太长，可以起别名吗？可以。
在 mybatis-config.xml  文件中使用 typeAliases 标签来起别名，包罗两种方式：
4.1 typeAliases 的第一种方式：typeAlias

1.    
2.     <typeAliases>
3. <mappers>
4.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
5.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
6.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
7. </mappers>  <typeAlias type="com.rainbowsea.mybatis.pojo.Car" alias="Car"></typeAlias>
8. <mappers>
9.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
10.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
11.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
12. </mappers>  <typeAlias type="com.rainbowsea.mybatis.pojo.Log" alias="Log"></typeAlias>
13.     </typeAliases>

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1. <?xml version="1.0" encoding="UTF-8" ?>
2. <!DOCTYPE configuration
3. <mappers>
4.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
5.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
6.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
7. </mappers>  PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
8. <mappers>
9.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
10.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
11.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
12. </mappers>  "http://mybatis.org/dtd/mybatis-3-config.dtd">
13. <configuration>
14.    
15.     <typeAliases>
16. <mappers>
17.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
18.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
19.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
20. </mappers>  
21. <mappers>
22.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
23.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
24.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
25. </mappers>  <package name="com.rainbowsea.mybatis.pojo"/>
26.     </typeAliases>
27.     <environments default="mybatis">
29. <mappers>
30.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
31.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
32.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
33. </mappers>  <environment id="mybatis">
34. <mappers>
35.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
36.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
37.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
38. </mappers><mappers>
39.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
40.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
41.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
42. </mappers>
43. <mappers>
44.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
45.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
46.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
47. </mappers><mappers>
48.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
49.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
50.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
51. </mappers><transactionManager type="JDBC"/>
52. <mappers>
53.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
54.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
55.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
56. </mappers><mappers>
57.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
58.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
59.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
60. </mappers><dataSource type="POOLED">
61. <mappers>
62.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
63.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
64.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
65. </mappers><mappers>
66.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
67.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
68.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
69. </mappers>    <property name="driver" value="com.mysql.cj.jdbc.Driver"/>
70. <mappers>
71.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
72.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
73.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
74. </mappers><mappers>
75.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
76.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
77.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
78. </mappers>    <property name="url" value="jdbc:mysql://localhost:3306/mybatis"/>
79. <mappers>
80.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
81.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
82.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
83. </mappers><mappers>
84.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
85.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
86.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
87. </mappers>    <property name="username" value="root"/>
88. <mappers>
89.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
90.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
91.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
92. </mappers><mappers>
93.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
94.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
95.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
96. </mappers>    <property name="password" value="MySQL123"/>
97. <mappers>
98.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
99.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
100.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
101. </mappers><mappers>
102.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
103.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
104.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
105. </mappers></dataSource>
106. <mappers>
107.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
108.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
109.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
110. </mappers>  </environment>
111.     </environments>
112.     <mappers>
113. <mappers>
114.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
115.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
116.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
117. </mappers>  
118. <mappers>
119.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
120.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
121.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
122. </mappers>  <mapper resource="CarMapper.xml"></mapper>
123.     </mappers>
124. </configuration><mappers>
125.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
126.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
127.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
128. </mappers>  

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• 首先要留意typeAliases标签的放置位置，如果不清楚的话，可以看看错误提示信息。
  
• typeAliases标签中的typeAlias可以写多个。
  
• typeAlias：
  
• 
  
  
  
  • type属性：指定给哪个类起别名
    
  • alias属性：别名。
    
  
  
• 
  
  
  
  • 
    
    
    
    • alias属性不是必须的，如果缺省的话，type属性指定的类型名的简类名作为别名。
      
    • alias是大小写不敏感的。也就是说假设alias="Car"，再用的时候，可以CAR，也可以car，也可以Car，都行、
      
    
    
  • 
    
  • 
    
  
  

留意：接口，一定要为全限定类名(带有包名)，不可以用别名机制
测试：

特殊的：  省略 alias 属性之后，别名就是类的简名了，比如 :com.rainbowsea.mybatis.pojo.Car 的别名就是 Car/CAR/cAR，不区分大小写的。

1.    
2.     <typeAliases>
3. <mappers>
4.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
5.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
6.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
7. </mappers>  <typeAlias type="com.rainbowsea.mybatis.pojo.Car" alias="Car"></typeAlias>
8. <mappers>
9.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
10.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
11.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
12. </mappers>  <typeAlias type="com.rainbowsea.mybatis.pojo.Log" alias="Log"></typeAlias>
13.     </typeAliases>   

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4.2 typeAliases 的第二种方式：package

如果一个包下的类太多，每个类都要起别名，会导致 typeAlias 标签配置较多，以是mybatis用提供package的配置方式，只需要指定包名，该包下的所有类都自动起别名，别名就是简类名。而且别名不区分大小写。
留意：接口，一定要为全限定类名(带有包名)，不可以用别名机制
这种方式是最常用的。

1.     <typeAliases>
2. <mappers>
3.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
4.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
5.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
6. </mappers>  
7. <mappers>
8.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
9.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
10.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
11. </mappers>  <package name="com.rainbowsea.mybatis.pojo"/>
12.     </typeAliases>

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测试：

留意：

使用 <?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
                PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
                "http://mybatis.org/dtd/mybatis-3-mapper.dtd">


<mapper namespace="">


       
</mapper>还可以将这个包下的所有的类的全部自动起别名，别名就是简名，不区分大小写
,所有的别名不区分大小写。但是：namespace 不能使用别名机制
同时需要按照一定的顺序放置，放到指定的顺序当中去

5. mappers 路径设置的使用

SQL映射文件的配置方式包罗四种：

• resource：从类路径中加载
  
• url：从指定的全限定资源路径中加载
  
• class：使用映射器接口实现类的完全限定类名
  
• package：将包内的映射器接口实现全部注册为映射器
  

5.1 mapper 标签下的 resource 属性的使用

这种方式是从类路径中加载配置文件，以是这种方式要求SQL映射文件必须放在resources目录下或其子目录下。

1. <mappers>
2.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
3.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
4.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
5. </mappers>

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5.2 mapper 标签下的 url 属性的使用

这种方式是一种绝对路径的方式，这种方式不要求配置文件必须放到类的路径当中，哪里都行，只要提供了一个绝对路径就行，这种方式使用少少，因为移植性太差了（并不是以是的系统都有盘符的说法的）。

**需要留意的是：要三个\\\ ，才表现两个 \\ **

1. <mappers>
2.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
3.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
4.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
5. </mappers>

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5.3 mapper 标签下的 class 属性的使用

Class: 这位置提供的是 mapper 接口的全限定接口名，必须带有包名（就是要一定要和对应接口的路径是一致的，一致的，一致的）
如果使用这种方式必须满足以下条件：

• SQL映射文件和mapper接口放在同一个目录下。
  
• SQL映射文件的名字也必须和mapper接口名一致。
  

1. <mappers>
2.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
3.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
4.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
5. </mappers><mappers>
6.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
7.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
8.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
9. </mappers>    如果你class指定是:com.rainbowsea.mybatis.mapper.CarMapper<mappers>
10.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
11.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
12.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
13. </mappers>  那么mybatis框架会自动去com/rainbowsea/mybatis/mapper/CarMapper/的目录下找，留意是 / 留意：也就是说，如果你接纳这种方式，那么你必须包管:CarMapper.xml文件和CarMapper接口必须在同一个目录下，而且名字也是一致的CarMapper接口——》CarMapper.xmlLogMapper接口——> LogMapper.xml

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提示：
在IDEA的resources 目录下新建多重目录的话，必须是如许创建:
com/rianbowsea/mybatis/mapper/
不然是
com.rianbowsea.mybatis.mapper 这是建包了

保持一致的同时，名称也要是一致的

1.    
2.     <typeAliases>
3. <mappers>
4.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
5.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
6.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
7. </mappers>  <typeAlias type="com.rainbowsea.mybatis.pojo.Car" alias="Car"></typeAlias>
8. <mappers>
9.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
10.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
11.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
12. </mappers>  <typeAlias type="com.rainbowsea.mybatis.pojo.Log" alias="Log"></typeAlias>
13.     </typeAliases>  

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测试运行：
运行步伐：正常！！！

5.4 package 标签的使用

如果class较多，可以使用这种package的方式，但前提条件和上一种（mapper 标签下的class 属性的使用）方式一样。
如果使用这种方式必须满足以下条件：

• SQL映射文件和mapper接口放在同一个目录下。
  
• SQL映射文件的名字也必须和mapper接口名一致。
  

这种方式是最常用的。

1. <mappers>
2.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
3.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
4.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
5. </mappers>  

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运行测试：

6. 在 IDEA 中自定义配置文件模板

mybatis-config.xml 和 SqlMapper.xml ，logback 文件可以在IDEA中提前创建好模板，以后通过模板创建配置文件。

mybatis 核心配置文件的模板内容 ：

1. <?xml version="1.0" encoding="UTF-8"?>
3. <configuration debug="false">
4.    
5.     <appender name="STDOUT" >
6. <mappers>
7.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
8.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
9.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
10. </mappers>  <encoder >
11. <mappers>
12.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
13.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
14.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
15. </mappers><mappers>
16.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
17.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
18.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
19. </mappers>
20. <mappers>
21.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
22.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
23.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
24. </mappers><mappers>
25.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
26.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
27.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
28. </mappers><pattern>%d{yyyy-MM-dd HH:mm:ss.SSS} [%thread] %-5level %logger{50} - %msg%n</pattern>
29. <mappers>
30.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
31.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
32.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
33. </mappers>  </encoder>
34.     </appender>
36.    
37.     <logger name="com.apache.ibatis" level="TRACE"/>
38.     <logger name="java.sql.Connection" level="DEBUG"/>
39.     <logger name="java.sql.Statement" level="DEBUG"/>
40.     <logger name="java.sql.PreparedStatement" level="DEBUG"/>
42.    
43.     <root level="DEBUG">
44. <mappers>
45.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
46.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
47.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
48. </mappers>  <appender-ref ref="STDOUT"/>
49. <mappers>
50.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
51.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
52.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
53. </mappers>  <appender-ref ref="FILE"/>
54.     </root>
56. </configuration>

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logback 的日记配置模板内容 ：

1. <?xml version="1.0" encoding="UTF-8"?>
3. <configuration debug="false">
4.    
5.     <appender name="STDOUT" >
6. <mappers>
7.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
8.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
9.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
10. </mappers>  <encoder >
11. <mappers>
12.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
13.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
14.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
15. </mappers><mappers>
16.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
17.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
18.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
19. </mappers>
20. <mappers>
21.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
22.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
23.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
24. </mappers><mappers>
25.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
26.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
27.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
28. </mappers><pattern>%d{yyyy-MM-dd HH:mm:ss.SSS} [%thread] %-5level %logger{50} - %msg%n</pattern>
29. <mappers>
30.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
31.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
32.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
33. </mappers>  </encoder>
34.     </appender>
36.    
37.     <logger name="com.apache.ibatis" level="TRACE"/>
38.     <logger name="java.sql.Connection" level="DEBUG"/>
39.     <logger name="java.sql.Statement" level="DEBUG"/>
40.     <logger name="java.sql.PreparedStatement" level="DEBUG"/>
42.    
43.     <root level="DEBUG">
44. <mappers>
45.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
46.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
47.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
48. </mappers>  <appender-ref ref="STDOUT"/>
49. <mappers>
50.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
51.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
52.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
53. </mappers>  <appender-ref ref="FILE"/>
54.     </root>
56. </configuration>

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SqLMapper的配置模板内容：

1. <?xml version="1.0" encoding="UTF-8" ?>
2. <!DOCTYPE mapper
3.                 PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
4.                 "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
7. <mapper namespace="">
10.        
11. </mapper>

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7. 补充：插入数据时获取自动天生的主键的值

**前提是：主键是自动天生的。 **
业务背景：一个用户有多个角色。

插入一条新的记录之后，自动天生了主键，而这个主键需要在其他表中使用时。
插入一个用户数据的同时需要给该用户分副角色：需要将天生的用户的id插入到角色表的user_id字段上。
第一种方式：可以先插入用户数据，再写一条查询语句获取id，然后再插入user_id字段。【比力麻烦】
第二种方式：mybatis提供了一种方式更加便捷。

1. <?xml version="1.0" encoding="UTF-8" ?>
2. <!DOCTYPE mapper
3.                 PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
4.                 "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
7. <mapper namespace="">
10.        
11. </mapper><?xml version="1.0" encoding="UTF-8" ?>
12. <!DOCTYPE mapper
13.                 PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
14.                 "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
17. <mapper namespace="">
20.        
21. </mapper><?xml version="1.0" encoding="UTF-8" ?>
22. <!DOCTYPE mapper
23.                 PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
24.                 "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
27. <mapper namespace="">
30.        
31. </mapper>insert into t_car values(null,#{carNum},#{brand},#{guidePrice},#{produceTime},#{carType})<?xml version="1.0" encoding="UTF-8" ?>
32. <!DOCTYPE mapper
33.                 PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
34.                 "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
37. <mapper namespace="">
40.        
41. </mapper>

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userGeneratedKeys = "true"  使用自动天生的主键值，false 则是不使用自动天生的主键值了
keyProperty="id" 指定主键值赋值给POJO类(ORM映射)对象的哪个属性，这个就表现将主键值给Car对象的 id属性。
留意：这个 keyProperty 指定的值，一定要和对应上的 pojo 对象类上的属性一致，不然，不可的。

1. package com.rainbowsea.mybatis.mapper;
3. import com.rainbowsea.mybatis.pojo.Car;
5. import java.util.List;
7. /**
8. * 封装汽车相关信息的pojo类，普通的Java类
9. */
10. public interface CarMapper {
12.     /**
13.      * 插入 Car 信息，并且使用生成的主键值
14.      * @param car
15.      * @return
16.      */
17.     int insertCarUserGeneratedKey(Car car);
19. }

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1. <mappers>
2.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
3.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
4.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
5. </mappers><mappers>
6.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
7.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
8.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
9. </mappers>    insert into t_car<mappers>
10.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
11.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
12.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
13. </mappers>  values (null, #{carNum}, #{brand}, #{guidePrice}, #{produceTime}, #{carType})   

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运行测试：

8. 总结：

• { } 与 ${ } 的区别和使用
  

1. - #{ } ：先编译 SQL 语句，再对占位符传值，底层是 PrepareedStatement 实现，可以防止 SQL 注入，比较常用
2. - ${ }：先进行SQL语句的拼接，然后再对SQL语句进行编译，底层是 Statement 实现，这种方式存在 SQL注入现象，SQL注入的风险，简单的说就是，直接将传入的值拼接为了SQL语句，然后再执行的）。只有在需要进行SQL语句关键字拼接的情况下才会用到。
3. - 简单的说一个区别就是：#{} 传的值是带有 '' 单引号的，而 ${} 传的值是（直接就是值，没有单引号，或者是双引号，两个都没有）

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• 什么情况下必须使用 $
  

1. 拼接表名
2. 批量删除
3. 模糊查询

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• typeAliases 别名定义的使用，留意：接口，一定要为全限定类名(带有包名)，不可以用别名机制 ，发起接纳第二种 package 方式，，同时留意：typeAliases 的正确顺序和位置，可以参考报错信息，进行修正。
  

1.     <typeAliases>
2. <mappers>
3.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
4.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
5.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
6. </mappers>  
7. <mappers>
8.   <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
9.   <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
10.   <mapper resource="org/mybatis/builder/PostMapper.xml"/>
11. </mappers>  <package name="com.rainbowsea.mybatis.pojo"/>
12.     </typeAliases>

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• mappers 路径设置的使用 ，发起接纳 package 标签的方式，留意条件，两个条件的一致性。
  

1. - SQL映射文件和mapper接口放在同一个目录下。
2. - SQL映射文件的名字也必须和mapper接口名一致。

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• 在 IDEA 中自定义配置文件模板
  
• 插入数据时获取自动天生的主键的值，**前提是：在对应数据表中的主键是自动天生的(自增的方式才行)。 **
  

1. <?xml version="1.0" encoding="UTF-8" ?>
2. <!DOCTYPE mapper
3.                 PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
4.                 "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
7. <mapper namespace="">
10.        
11. </mapper><?xml version="1.0" encoding="UTF-8" ?>
12. <!DOCTYPE mapper
13.                 PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
14.                 "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
17. <mapper namespace="">
20.        
21. </mapper><?xml version="1.0" encoding="UTF-8" ?>
22. <!DOCTYPE mapper
23.                 PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
24.                 "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
27. <mapper namespace="">
30.        
31. </mapper>insert into t_car values(null,#{carNum},#{brand},#{guidePrice},#{produceTime},#{carType})<?xml version="1.0" encoding="UTF-8" ?>
32. <!DOCTYPE mapper
33.                 PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
34.                 "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
37. <mapper namespace="">
40.        
41. </mapper>

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9. 最后：

“在这个最后的篇章中，我要表达我对每一位读者的感激之情。你们的关注和回复是我创作的动力源泉，我从你们身上吸取了无尽的灵感与勇气。我会将你们的鼓励留在心底，继续在其他的领域奋斗。感谢你们，我们总会在某个时候再次相遇。”

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