Spring Boot学习随笔- 集成MyBatis-Plus（二）条件查询QueryWrapper、聚合
学习视频：【编程不良人】Mybatis-Plus整合SpringBoot实战教程,提高的你开发效率,后端人员必备!查询方法详解
<ul>普通查询
// 根据主键id去查询单个结果的。
@Test
public void selectById() {
User user = userMapper.selectById(1739970502337392641L);
System.out.println(user);
}
//根据多个主键id批量查询结果的
@Test
public void selectIds() {
List<Long> list = Arrays.asList(1739970502337392641L, 1739983903621038082L, 1739984905459900417L);
List<User> userList = userMapper.selectBatchIds(list);
userList.forEach(System.out::println);
}
// 根据多个条件查询结果的
@Test
public void selectByMap() {
// map.put("name","小明")
// map.put("age",30)
// 相当于 where name ="小明" and age=30
Map<String, Object> columnMap = new HashMap<>();
columnMap.put("name", "小刚");
columnMap.put("age", "18");
List<User> userList = userMapper.selectByMap(columnMap);
userList.forEach(System.out::println);
}条件构造器查询 【重要】
AbstractWrapper 是 MyBatis Plus 中的一个抽象类，用于构建 SQL 查询条件。定义了泛型 T、C 和 Children。其中，T 表示实体类的类型，C 表示查询条件的类型，Children 表示子类的类型，用于支持链式调用。它提供了一系列方法，用于构建 SQL 查询条件，包括设置查询字段、设置查询条件、排序等。
常用实现类包括 QueryWrapper 和 UpdateWrapper。这两个类都是 MyBatis Plus 提供的具体实现，用于构建查询条件和更新条件。
条件构造器查询示例
@SpringBootTest
public class SelectTests {
@Autowired
private UserMapper userMapper;
/**
* 1.名字中包含刘且年龄大于20
* name like '%刘%' and age>20
*/
@Test
public void selectByWrapper() {
// 创建queryWrapper的两种方式
QueryWrapper<User> queryWrapper = new QueryWrapper<>();
// QueryWrapper<User> queryWrapper1 = Wrappers.<User>query();
queryWrapper.like("name", "刘").gt("age", 20);
List<User> list = userMapper.selectList(queryWrapper);
list.forEach(System.out::println);
}
/**
* 2.名字中包含刘且年龄大于等于20且小于30并且email不为空
* name like ‘%刘’ and age between 20 and 30 and email is not null
*/
@Test
public void selectByWrapper2() {
QueryWrapper<User> queryWrapper = new QueryWrapper<>();
queryWrapper.like("name", "刘").between("age", 20, 30).isNull("email");
List<User> list = userMapper.selectList(queryWrapper);
list.forEach(System.out::println);
}
/**
* 3.名字中包含刘或年龄大于等于20,按照年龄降序排序，年龄相同按照id升序排列
* name like ‘%刘’ and age between 20 and 30 and email is not null
*/
@Test
public void selectByWrapper3() {
QueryWrapper<User> queryWrapper = new QueryWrapper<>();
queryWrapper.like("name", "刘").or().ge("age",20)
.orderByDesc("age")
.orderByAsc("user_id");
List<User> list = userMapper.selectList(queryWrapper);
list.forEach(System.out::println);
}
/**
* 4.创建日期为2023年12月17日并且直属上级为王姓
* date_format(create_time,'%Y-%m-$d') and manager_id in(select id from user where name like '王%'
*/
@Test
public void selectByWrapper4() {
QueryWrapper<User> queryWrapper = new QueryWrapper<>();
queryWrapper.apply("date_format(create_time,'%Y-%m-%d')={0}", "2023-12-27") //使用占位符避免sql注入的风险
.inSql("manager_id","select user_id from mp_user where name like '王%'");
List<User> list = userMapper.selectList(queryWrapper);
list.forEach(System.out::println);
}
/**
* 5.名字为刘姓且年龄小于30或者邮箱不为空
* name like '王%' and (age<20 or email is not null)
*/
@Test
public void selectByWrapper5() {
QueryWrapper<User> queryWrapper = new QueryWrapper<>();
queryWrapper.likeRight("name", "刘")
.and(wq -> wq.lt("age", 30).or().isNotNull("email"));
List<User> list = userMapper.selectList(queryWrapper);
list.forEach(System.out::println);
}
/**
* 6.名字为刘姓或者（年龄小于30且大于20并且邮箱不为空）
* name like '刘%' or (age<30 and age>20 and email is not null)
*/
@Test
public void selectByWrapper6() {
QueryWrapper<User> queryWrapper = new QueryWrapper<>();
queryWrapper.likeRight("name", "刘")
.or(wq -> wq.lt("age", 30).gt("age", 20)
.isNotNull("email"));
List<User> list = userMapper.selectList(queryWrapper);
list.forEach(System.out::println);
}
/**
* 7.（年龄小于30且邮箱不为空）并且名字为刘姓
*(age<30 or email is not null) and name like '刘%'
*/
@Test
public void selectByWrapper7() {
QueryWrapper<User> queryWrapper = new QueryWrapper<>();
queryWrapper.nested(wq -> wq.lt("age", 30)
.or().isNotNull("email"))
.likeRight("name", "刘");
List<User> list = userMapper.selectList(queryWrapper);
list.forEach(System.out::println);
}
/**
* 8. 年龄为 21 25 33
*age in(21,25,33)
*/
@Test
public void selectByWrapper8() {
QueryWrapper<User> queryWrapper = new QueryWrapper<>();
queryWrapper.in("age", 21, 25, 33);
List<User> list = userMapper.selectList(queryWrapper);
list.forEach(System.out::println);
}
/**
* 9. 只返回满足条件的其中一条语句即可
*limit 1
*/
@Test
public void selectByWrapper9() {
QueryWrapper<User> queryWrapper = new QueryWrapper<>();
queryWrapper.in("age", 21, 25, 33).last("limit 1"); // last() 有sql注入的风险，谨慎使用
List<User> list = userMapper.selectList(queryWrapper);
list.forEach(System.out::println);
}
}select 不列出全部字段
/**
* 10.名字中包含刘且年龄小于30（需求1加强版）
*/
@Test
public void selectByWrapper() {
QueryWrapper<User> queryWrapper = new QueryWrapper<>();
// queryWrapper.select("user_id","name","age").like("name", "刘").lt("age", 30); // 包含字段
queryWrapper.like("name", "刘").lt("age", 30)
.select(User.class, info ->
!info.getColumn().equals("create_time") && !info.getColumn().equals("manager_id"));// 排除字段
List<User> list = userMapper.selectList(queryWrapper);
list.forEach(System.out::println);
}condition作用
根据判断决定查询条件是否加到sql语句里面
@Test
public void testCondition() {
String name = "东";
String email = "";
condition(name, email);
}
private void condition(String name, String email) {
QueryWrapper<User> queryWrapper = new QueryWrapper<>();
// if (StringUtils.isNotEmpty(name)) {
// queryWrapper.like("name", name);
// }
// if (StringUtils.isNotEmpty(email)) {
// queryWrapper.like("email", email);
// }
queryWrapper.like(StringUtils.isNotEmpty(name), "name", name)
.like(StringUtils.isNotEmpty(email), "email", email);
List<User> list = userMapper.selectList(queryWrapper);
list.forEach(System.out::println);
}实体作为条件构造器构造方法的参数
@Test
public void selectByWrapperEntity() {
User user = new User();
user.setRealName("小刚");
user.setAge(18);
QueryWrapper<User> queryWrapper = new QueryWrapper<>(user);
List<User> list = userMapper.selectList(queryWrapper);
list.forEach(System.out::println);
}
运行结果的sql语句：SELECT * FROM mp_user WHERE **name=? AND age=?**
会把set注入的属性和值映射到where条件中<ul>通过SqlCondition 更改查询条件
https://img2023.cnblogs.com/blog/3321544/202312/3321544-20231230173158823-916180260.png
用法@TableField(condition = SqlCondition.LIKE)private String name;@TableField(condition = "%s<#{%s}") //根据定义的常量，自己也可以参考并更改private Integer age;运行结果：SELECT * FROM mp_user WHERE **name LIKE CONCAT('%',?,'%')** AND AND age
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