jpa双向多对多关联关系

1.1.  关系维护方

Teacher.java

package com.morris.entity; import java.util.Set; import javax.persistence.CascadeType; import javax.persistence.Column; 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; @Entity public class Teacher { @Id @GeneratedValue private Integer id; @Column(name="name",length=50,nullable=false) private String name; @ManyToMany(cascade=CascadeType.REFRESH,fetch=FetchType.LAZY) @JoinTable(name="stu_tea",joinColumns=@JoinColumn(name="stu_id"),inverseJoinColumns=@JoinColumn(name="tea_id")) private Set<Student> students; @Override public String toString() { return "Teacher [id=" + id + ", name=" + name + "]"; } public Teacher() { super(); // TODO Auto-generated constructor stub } public Teacher(String name) { super(); this.name = name; } public Set<Student> getStudents() { return students; } public void setStudents(Set<Student> students) { this.students = students; } public Integer getId() { return id; } public void setId(Integer id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } }

1.2.  关系被维护方

Student.java

package com.morris.entity; import java.util.Set; import javax.persistence.CascadeType; import javax.persistence.Column; import javax.persistence.Entity; import javax.persistence.FetchType; import javax.persistence.GeneratedValue; import javax.persistence.Id; import javax.persistence.ManyToMany; @Entity public class Student { @Id @GeneratedValue private Integer id; @Column(name="name",nullable=false,length=50) private String name; @ManyToMany(cascade=CascadeType.REFRESH,fetch=FetchType.LAZY,mappedBy="students") private Set<Teacher> teachers; public Integer getId() { return id; } public void setId(Integer id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } public Student(String name) { super(); this.name = name; } public Set<Teacher> getTeachers() { return teachers; } public void setTeachers(Set<Teacher> teachers) { this.teachers = teachers; } public Student() { super(); // TODO Auto-generated constructor stub } @Override public String toString() { return "Student [id=" + id + ", name=" + name + "]"; } }

1.3.  测试

Many2ManyTest.java

package com.morris.test; import static org.junit.Assert.*; import java.util.HashSet; import java.util.Set; import javax.persistence.EntityManager; import javax.persistence.EntityManagerFactory; import javax.persistence.Persistence; import org.junit.AfterClass; import org.junit.BeforeClass; import org.junit.Test; import com.morris.entity.Student; import com.morris.entity.Teacher; public class Many2ManyTest { private static EntityManagerFactory entityManagerFactory; private static EntityManager entityManager; @BeforeClass public static void setUpBeforeClass() throws Exception { entityManagerFactory = Persistence.createEntityManagerFactory("jpaDemo"); entityManager = entityManagerFactory.createEntityManager(); entityManager.getTransaction().begin(); } @Test public void test() { Teacher teacher = new Teacher("张三"); Student student = new Student("李四"); entityManager.persist(teacher); entityManager.persist(student); Set<Student> students = new HashSet<Student>(); students.add(student); teacher.setStudents(students); } @AfterClass public static void tearDownAfterClass() throws Exception { entityManager.getTransaction().commit(); entityManager.close(); entityManagerFactory.close(); } }