JPA 入门实战(2)--简单使用

本文主要介绍 JPA 的实际使用，相关的环境及软件信息如下：JPA 2.2(eclipselink 2.7.10、hibernate-entitymanager 5.6.10.Final、openjpa 3.2.2)，JPA 3.0(eclipselink 3.0.2、hibernate-core-jakarta 5.6.10.Final)。
1、JPA 2.2 使用

工程目录结构如下：

1.1、引入依赖

这里使用 eclipselink 作为 JPA 的实现框架。

1. <dependency>
2.     <groupId>org.eclipse.persistence</groupId>
3.     <artifactId>org.eclipse.persistence.jpa</artifactId>
4.     <version>2.7.10</version>
5. </dependency>

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其他的依赖可自行引入，如数据库驱动、lombok 等。
1.2、创建实体类

1.2.1、Student.java

1. package com.abc.demojpa.entity;
3. import lombok.AllArgsConstructor;
4. import lombok.Data;
5. import lombok.NoArgsConstructor;
6. import org.hibernate.annotations.CreationTimestamp;
7. import org.hibernate.annotations.UpdateTimestamp;
9. import javax.persistence.*;
10. import java.time.LocalDateTime;
12. @NoArgsConstructor
13. @AllArgsConstructor
14. @Data
15. @Entity
16. @Table(name = "a_student")
17. @NamedQuery(name = "queryAll", query = "select s from Student s")
18. public class Student {
19.     @Id
20.     @GeneratedValue
21.     private Long id;
23.     @Column(name = "create_time")
24.     private LocalDateTime createTime;
26.     @Column(name = "modify_time")
27.     private LocalDateTime modifyTime;
29.     private String name;
31.     private Integer age;
33.     @Column(name = "home_address")
34.     private String homeAddress;
35. }

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1.2.2、BaseEntity.java

1. package com.abc.demojpa.entity;
3. import lombok.Data;
5. import javax.persistence.Column;
6. import javax.persistence.GeneratedValue;
7. import javax.persistence.Id;
8. import javax.persistence.MappedSuperclass;
9. import java.time.LocalDateTime;
11. @Data
12. //该类的属性都将映射到其子类的数据库字段中
13. @MappedSuperclass
14. public class BaseEntity {
15.     @Id
16.     @GeneratedValue
17.     private Long id;
19.     @Column(name = "create_time")
20.     private LocalDateTime createTime;
21. }

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1.2.3、Teacher.java

Teacher 继承了 BaseEntity，主要为了测试属性的继承。

1. package com.abc.demojpa.entity;
3. import lombok.Data;
4. import lombok.NoArgsConstructor;
6. import javax.persistence.*;
8. @NoArgsConstructor
9. @Data
10. @Entity
11. @Table(name = "a_teacher")
12. public class Teacher extends BaseEntity {
13.     private String name;
15.     private Integer age;
16. }

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1.3、编写 JPA 配置文件 (persistence.xml)

该配置文件需放在 META-INF 目录下。

1. <?xml version="1.0" encoding="UTF-8"?>
2. <persistence version="2.2"
3.              xmlns="http://xmlns.jcp.org/xml/ns/persistence"
4.              xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
5.              xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/persistence http://xmlns.jcp.org/xml/ns/persistence/persistence_2_2.xsd">
6.     <persistence-unit name="myUnit">
7.         <provider>org.eclipse.persistence.jpa.PersistenceProvider</provider>
8.         <class>com.abc.demojpa.entity.Student</class>
9.         <class>com.abc.demojpa.entity.Teacher</class>
10.         <properties>
11.             <property name="javax.persistence.jdbc.driver" value="com.mysql.cj.jdbc.Driver"/>
12.             <property name="javax.persistence.jdbc.url" value="jdbc:mysql://10.49.196.10:3306/test?useUnicode=true&characterEncoding=UTF-8"/>
13.             <property name="javax.persistence.jdbc.user" value="root"/>
14.             <property name="javax.persistence.jdbc.password" value="123456"/>
15.             <property name="eclipselink.logging.level" value="INFO" />
16.             <property name="eclipselink.ddl-generation" value="create-or-extend-tables" />
17.         </properties>
18.     </persistence-unit>
19. </persistence>

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eclipselink 开头的配置是 eclipselink 自带的扩展配置，用于实现功能的增强；详细的扩展配置说明可参考官网说明：https://www.eclipse.org/eclipselink/documentation/2.7/jpa/extensions/toc.htm。
1.4、使用例子

1.4.1、插入实体

1. @Test
2. public void persist() {
3.     entityManager.getTransaction().begin();
4.     Student student = new Student();
5.     student.setName("小明");
6.     student.setCreateTime(LocalDateTime.now());
7.     student.setModifyTime(LocalDateTime.now());
8.     student.setAge(15);
9.     student.setHomeAddress("江苏");
11.     Student student2 = new Student();
12.     student2.setName("小红");
13.     student2.setAge(18);
14.     student2.setHomeAddress("广东");
16.     Teacher teacher = new Teacher();
17.     teacher.setCreateTime(LocalDateTime.now());
18.     teacher.setName("张三");
19.     teacher.setAge(35);
21.     entityManager.persist(student);
22.     entityManager.persist(student2);
23.     entityManager.persist(teacher);
25.     entityManager.getTransaction().commit();
26. }

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1.4.2、查询实体

1. @Test
2. public void find() {
3.     Student student = entityManager.find(Student.class, 1501L);
4.     logger.info("student={}", student);
5. }

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1.4.3、更新实体(先查再更新)

1. @Test
2. public void modify() {
3.     entityManager.getTransaction().begin();
4.     Student student = entityManager.find(Student.class, 1501L);
5.     student.setName("小明2");
6.     entityManager.getTransaction().commit();
7. }

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1.4.4、更新实体(直接根据id更新)

1. @Test
2. public void merge() {
3.     entityManager.getTransaction().begin();
4.     Student student = new Student();
5.     student.setId(1501L);
6.     student.setName("小明3");
7.     student.setAge(16);
8.     entityManager.merge(student);
9.     entityManager.getTransaction().commit();
10. }

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1.4.5、删除实体

1. @Test
2. public void remove() {
3.     entityManager.getTransaction().begin();
4.     Student student = entityManager.find(Student.class, 1501L);
5.     entityManager.remove(student);
6.     entityManager.getTransaction().commit();
7. }

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1.4.6、JPQL 查询

1. @Test
2. public void select() {
3.     //查询一个字段
4.     Query query = entityManager.createQuery("select s.name from Student s where s.age>10", String.class);
5.     List<String> result = query.getResultList();
6.     logger.info("result={}", result);
8.     //查询多个字段 (?n 占位符：传统 ? 占位符的改良占位符，仅仅适应 JPQL 查询)
9.     query = entityManager.createQuery("select s.name,s.homeAddress from Student s where s.age>?1 and s.name like ?2", Object[].class);
10.     query.setParameter(1, 10);
11.     query.setParameter(2, "%小%");
12.     List<Object[]> result2 = query.getResultList();
13.     for (Object[] arr : result2) {
14.         String s = "";
15.         for (Object o : arr) {
16.             s += o.toString() + ",";
17.         }
18.         logger.info(s);
19.     }
21.     //查询对象 (:name 占位符：变量名形式的占位符，仅仅适应 JPQL 查询)
22.     query = entityManager.createQuery("select s.name,s.homeAddress from Student s where s.age between :min and :max and s.name like '%小%' order by s.id", Student.class);
23.     query.setParameter("min", 10);
24.     query.setParameter("max", 40);
25.     //设置结果的开始位置，最大记录条数，可用来实现分页
26.     query.setFirstResult(0);
27.     query.setMaxResults(10);
28.     List<Student> result3 = query.getResultList();
29.     logger.info("result3={}", result3);
31.     //聚合操作
32.     query = entityManager.createQuery("select max(s.age) from Student s");
33.     Object result4 = query.getSingleResult();
34.     logger.info("result4={}", result4);
36.     //对应Student实体类中定义的静态查询”queryAll“
37.     query = entityManager.createNamedQuery("queryAll");
38.     List<Student> result5 = query.getResultList();
39.     logger.info("result5={}", result5);
40. }

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1.4.7、JPQL 更新

1. @Test
2. public void update() {
3.     entityManager.getTransaction().begin();
4.     Query query = entityManager.createQuery( "update Student SET age=16 where name='小明'");
5.     query.executeUpdate();
6.     entityManager.getTransaction().commit();
7. }

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1.4.8、JPQL 删除

1. @Test
2. public void delete() {
3.     entityManager.getTransaction().begin();
4.     Query query = entityManager.createQuery( "delete from Student where id=1501");
5.     query.executeUpdate();
6.     entityManager.getTransaction().commit();
7. }

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1.4.9、JPQL 本地查询,直接 SQL 语句查询数据

1. @Test
2. public void nativeSelect() {
3.     Query query = entityManager.createNativeQuery("select s.* from a_student s where s.age>?", Student.class);
4.     query.setParameter(1, 10);
5.     List<Student> result = query.getResultList();
6.     logger.info("result={}", result);
7. }

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1.4.10、JPA 标准 API 使用一

类似 SQL：select name from student where name='小明'

1. @Test
2. public void criteria() {
3.     CriteriaBuilder criteriaBuilder = entityManager.getCriteriaBuilder();
4.     CriteriaQuery<String> criteriaQuery = criteriaBuilder.createQuery(String.class);
5.     Root<Student> root = criteriaQuery.from(Student.class);
6.     criteriaQuery.select(root.get("name"));
7.     criteriaQuery.where(criteriaBuilder.equal(root.get("name"), "小明"));
8.     TypedQuery<String> query = entityManager.createQuery(criteriaQuery);
9.     List<String> list = query.getResultList();
10.     logger.info(list.toString());
11. }

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1.4.11、JPA 标准 API 使用二

类似 SQL：select id,name,age from student where age>=10 order by age,name desc

1. @Test
2. public void criteria2() {
3.     CriteriaBuilder criteriaBuilder = entityManager.getCriteriaBuilder();
4.     CriteriaQuery<Student> criteriaQuery = criteriaBuilder.createQuery(Student.class);
5.     Root<Student> root = criteriaQuery.from(Student.class);
6.     //Student 实体类需要有对应的构造方法
7.     criteriaQuery.multiselect(root.get("id"), root.get("name"), root.get("age"), root.get("homeAddress"));
8.     criteriaQuery.where(criteriaBuilder.ge(root.get("age"), 10));
9.     criteriaQuery.orderBy(criteriaBuilder.asc(root.get("age"))).orderBy(criteriaBuilder.desc(root.get("name")));
10.     TypedQuery<Student> query = entityManager.createQuery(criteriaQuery);
11.     List<Student> list = query.getResultList();
12.     logger.info(list.toString());
13. }

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1.4.12、JPA 标准 API 使用三


类似 SQL：select age,count(*) from student group by age having age=10 order by age,name desc     */    @Test    public void criteria2() {        CriteriaBuilder criteriaBuilder = entityManager.getCriteriaBuilder();        CriteriaQuery criteriaQuery = criteriaBuilder.createQuery(Student.class);        Root root = criteriaQuery.from(Student.class);        //Student 实体类需要有对应的构造方法        criteriaQuery.multiselect(root.get("id"), root.get("name"), root.get("age"), root.get("homeAddress"));        criteriaQuery.where(criteriaBuilder.ge(root.get("age"), 10));        criteriaQuery.orderBy(criteriaBuilder.asc(root.get("age"))).orderBy(criteriaBuilder.desc(root.get("name")));        TypedQuery query = entityManager.createQuery(criteriaQuery);        List list = query.getResultList();        logger.info(list.toString());    }    /**     * Criteria API     * select age,count(*) from student group by age having age