JPA中的@ManyToMany
@ManyToMany注释表示模型类是多对多关系的一端。
@JoinTable 描述了多对多关系的数据表关系。
- name 属性指定中间表名称
- joinColumns 定义中间表与Teacher 表的外键关系
- inverseJoinColumns属性定义了中间表与另外一端(Student)的外键关系
单向多对多表的ddl语句
CREATE TABLE `t_student` (
`id` bigint(20) NOT NULL AUTO_INCREMENT,
`sname` varchar(255) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8;
CREATE TABLE `t_teacher` (
`id` bigint(20) NOT NULL AUTO_INCREMENT,
`tname` varchar(255) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=utf8;
CREATE TABLE `t_teacher_student` (
`teacher_id` bigint(20) NOT NULL,
`student_id` bigint(20) NOT NULL,
PRIMARY KEY (`teacher_id`,`student_id`),
KEY `FK_o82lxg0wi1y88lit4fy7lkg7t` (`student_id`),
CONSTRAINT `FK_1epgkih044inndyv1dtihcb7r` FOREIGN KEY (`teacher_id`) REFERENCES `t_teacher` (`id`),
CONSTRAINT `FK_o82lxg0wi1y88lit4fy7lkg7t` FOREIGN KEY (`student_id`) REFERENCES `t_student` (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
Student
package com.jege.jpa.many2many;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.Table;
/**
* @author JE哥
* @email 1272434821@qq.com
* @description:单向
*/
@Entity
@Table(name = "t_student")
public class Student {
@Id
@GeneratedValue
private Long id;
private String sname;
public Student() {
}
public Student(String sname) {
this.sname = sname;
}
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
public String getSname() {
return sname;
}
public void setSname(String sname) {
this.sname = sname;
}
@Override
public String toString() {
return "Student [id=" + id + ", sname=" + sname + "]";
}
}Teacher
package com.jege.jpa.many2many;
import java.util.HashSet;
import java.util.Set;
import javax.persistence.CascadeType;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.JoinTable;
import javax.persistence.ManyToMany;
import javax.persistence.Table;
/**
* @author JE哥
* @email 1272434821@qq.com
* @description:单向:一个老师教多个学生
*/
@Entity
@Table(name = "t_teacher")
public class Teacher {
@Id
@GeneratedValue
private Long id;
private String tname;
// @ManyToMany注释表示Teacher是多对多关系的一端。
// @JoinTable描述了多对多关系的数据表关系。name属性指定中间表名称，joinColumns定义中间表与Teacher表的外键关系。
// 中间表Teacher_Student的Teacher_ID列是Teacher表的主键列对应的外键列，inverseJoinColumns属性定义了中间表与另外一端(Student)的外键关系。
@ManyToMany(cascade = CascadeType.PERSIST, fetch = FetchType.LAZY)
@JoinTable(name = "t_teacher_student", joinColumns = { @JoinColumn(name = "teacher_id") }, inverseJoinColumns = {
@JoinColumn(name = "student_id") })
private Set<Student> students = new HashSet<Student>();
public Teacher() {
}
public Teacher(String tname) {
this.tname = tname;
}
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
public String getTname() {
return tname;
}
public void setTname(String tname) {
this.tname = tname;
}
public Set<Student> getStudents() {
return students;
}
public void setStudents(Set<Student> students) {
this.students = students;
}
@Override
public String toString() {
return "Teacher [id=" + id + ", tname=" + tname + "]";
}
}Many2ManyTest
package com.jege.jpa.many2many;
import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;
import org.junit.After;
import org.junit.AfterClass;
import org.junit.BeforeClass;
import org.junit.Test;
/**
* @author JE哥
* @email 1272434821@qq.com
* @description:单向多对多Test
*/
public class Many2ManyTest {
private static EntityManagerFactory entityManagerFactory = null;
private EntityManager entityManager = null;
@BeforeClass
public static void setUpBeforeClass() throws Exception {
entityManagerFactory = Persistence.createEntityManagerFactory("com.jege.jpa");
}
// t1老师教2个学生s1,s2
// t2老师教3个学生s1,s2,s3
// 总共10条insert
@Test
public void persist() throws Exception {
entityManager = entityManagerFactory.createEntityManager();
entityManager.getTransaction().begin();
Teacher t1 = new Teacher("t1");
Teacher t2 = new Teacher("t2");
Student s1 = new Student("s1");
Student s2 = new Student("s2");
Student s3 = new Student("s3");
entityManager.persist(t1);
entityManager.persist(t2);
entityManager.persist(s1);
entityManager.persist(s2);
entityManager.persist(s3);// 全部发出5条insert单表
// 添加中间表
// t1老师教2个学生s1,s2
// t2老师教3个学生s1,s2,s3
t1.getStudents().add(s1);
t1.getStudents().add(s2);
t2.getStudents().add(s1);
t2.getStudents().add(s2);
t2.getStudents().add(s3);
entityManager.getTransaction().commit();// 发出5条insert中间表
entityManager.close();
}
// t1老师教2个学生s1,s2
// 修改为 教2个学生s1,s3:先删除在添加
@Test
public void update() throws Exception {
persist();
entityManager = entityManagerFactory.createEntityManager();
entityManager.getTransaction().begin();
Teacher t1 = entityManager.find(Teacher.class, 1L);
Student s2 = entityManager.find(Student.class, 2L);
Student s3 = entityManager.find(Student.class, 3L);
// 删除
t1.getStudents().remove(s2);
// 添加
t1.getStudents().add(s3);
entityManager.getTransaction().commit();
}
// 删除t1的教的所有学生
@Test
public void delete() throws Exception {
persist();
entityManager = entityManagerFactory.createEntityManager();
entityManager.getTransaction().begin();
Teacher t1 = entityManager.find(Teacher.class, 1L);
t1.getStudents().clear();
entityManager.getTransaction().commit();
}
@After
public void tearDown() throws Exception {
if (entityManager != null && entityManager.isOpen())
entityManager.close();
}
@AfterClass
public static void tearDownAfterClass() throws Exception {
if (entityManagerFactory != null && entityManagerFactory.isOpen())
entityManagerFactory.close();
}
}
源码地址
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