JPA 菜鸟教程 7 双向多对多

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双向多对多的ddl语句

同单向多对多表的ddl语句一致

Student

package com.jege.jpa.many2many;import java.util.HashSet;import java.util.Set;import javax.persistence.Entity;import javax.persistence.GeneratedValue;import javax.persistence.Id;import javax.persistence.ManyToMany;import javax.persistence.Table;/** * @author JE哥 * @email [e-mail] * @description:双向：关系被维护端:不能操作中间表 */@Entity@Table(name = "t_student")public class Student {  @Id  @GeneratedValue  private Long id;  private String sname;  @ManyToMany(mappedBy = "students")  private Set<Teacher> teachers = new HashSet<Teacher>();  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;  }  public Set<Teacher> getTeachers() {    return teachers;  }  public void setTeachers(Set<Teacher> teachers) {    this.teachers = teachers;  }  @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 [e-mail] * @description:双向：关系维护端:可以操作中间表 */@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.Before;import org.junit.BeforeClass;import org.junit.Test;/** * @author JE哥 * @email [e-mail] * @description:双向多对多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");  }  @Before  public void setUp() throws Exception {    entityManager = entityManagerFactory.createEntityManager();  }  // 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.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.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.getTransaction().begin();    Teacher t1 = entityManager.find(Teacher.class, 1L);    t1.getStudents().clear();    entityManager.getTransaction().commit();  }  // insert 3条，单表插入,中间表无反应  // 因为Student是关系被维护端:不能操作中间表  @Test  public void persist2() throws Exception {    Teacher teacher = new Teacher("t1");    Student student1 = new Student("s1");    Student student2 = new Student("s2");    student1.getTeachers().add(teacher);// 插入中间表    student2.getTeachers().add(teacher);    entityManager.getTransaction().begin();    entityManager.persist(teacher);    entityManager.persist(student1);    entityManager.persist(student2);    entityManager.getTransaction().commit();  }  @Test  public void find() throws Exception {    persist();    entityManager = entityManagerFactory.createEntityManager();    Teacher teacher = entityManager.find(Teacher.class, 1L);    System.out.println(teacher.getTname());    System.out.println("------------------");    System.out.println(teacher.getStudents());  }  @Test  public void find2() throws Exception {    persist();    entityManager = entityManagerFactory.createEntityManager();    Student student = entityManager.find(Student.class, 1L);    System.out.println(student.getSname());    System.out.println("------------------");    System.out.println(student.getTeachers());  }  @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();  }}

其他关联项目

• * JPA 菜鸟教程 6 单向多对多*
  http://blog.csdn.net/je_ge/article/details/53495237

源码地址

https://github.com/je-ge/jpa

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