hibernate多对多（ManyToMany）注解开发

hibernate多对多注解开发小Demo。上代码

Student.java

package com.it.hibernate.domain;

import java.util.HashSet;
import java.util.Set;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.JoinTable;
import javax.persistence.ManyToMany;
import javax.persistence.Table;
@Entity
@Table(name="c_student")
public class Student {
	@GeneratedValue(strategy=GenerationType.IDENTITY)
	@Id
	//@Column(name="s_id")
	private Integer id;
	@Column(name="s_name")
	private String name;
	@ManyToMany(targetEntity=Teacher.class)
	// 使用JoinTabl来描述中间表，并描述中间表中外键与Student,Teacher的映射关系
	// joinColumns它是用来描述Student与中间表中的映射关系
	// inverseJoinColums它是用来描述Teacher与中间表中的映射关系
	@JoinTable(name="s_t",
	joinColumns={@JoinColumn(name="c_s_id",referencedColumnName="id")},
	inverseJoinColumns={@JoinColumn(name="c_t_id",referencedColumnName="id")}
			)
	private Set t = new HashSet();
	public Student() {
		super();
		// TODO Auto-generated constructor stub
	}
	public Student(Integer id, String name, Set t) {
		super();
		this.id = id;
		this.name = name;
		this.t = t;
	}
	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 Set getT() {
		return t;
	}
	public void setT(Set t) {
		this.t = t;
	}
	
	

}

Teacher.java

package com.it.hibernate.domain;

import java.util.HashSet;
import java.util.Set;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.ManyToMany;
import javax.persistence.Table;

import org.hibernate.annotations.Cascade;
import org.hibernate.annotations.CascadeType;
import org.hibernate.annotations.GenericGenerator;
@Entity
@Table(name="c_teacher")
public class Teacher {
	@Id
	@GenericGenerator(name="myuuid",strategy="uuid")
	@GeneratedValue(generator="myuuid") //引入自定义主键生成策略
	//@Column(name="t_id")
	private String id;
	@Column(name="t_name")
	private String name;
	@ManyToMany(targetEntity=Student.class,mappedBy="t") //让student维护外键表
	@Cascade(CascadeType.ALL)
	private Set students = new HashSet();
	public Teacher() {
		super();
		// TODO Auto-generated constructor stub
	}
	public Teacher(String id, String name, Set students) {
		super();
		this.id = id;
		this.name = name;
		this.students = students;
	}
	public String getId() {
		return id;
	}
	public void setId(String id) {
		this.id = id;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public Set getStudents() {
		return students;
	}
	public void setStudents(Set students) {
		this.students = students;
	}
	
	
	
	

}

1、测试级联保存

@Test
	public void test1() {
		// 获得持久化接口对象，并开启事务
		Session session = HibernateUtils.openSession();
		session.beginTransaction();
		// 操作
		Teacher t1 = new Teacher();
		t1.setName("张老师");
		Teacher t2 = new Teacher();
		t2.setName("李老师");

		Student s1 = new Student();
		s1.setName("张学生");
		Student s2 = new Student();
		s2.setName("李学生");

		// 维护外键(不执行外键维护的话，中间表没有数据)
		s1.getT().add(t1);
		s2.getT().add(t2);
		// 级联保存
		t1.getStudents().add(s1);
		t2.getStudents().add(s2);
		session.save(t1);
		session.save(t2);
		// 提交事务，并关闭持久化接口对象
		session.getTransaction().commit();
		session.close();

结果：

2、测试级联删除

	@Test
	public void del() {
		// 获得持久化接口对象，并开启事务
		Session session = HibernateUtils.openSession();
		session.beginTransaction();
		// 操作
		Student s = session.get(Student.class, 1);
		
		session.delete(s);
		// 提交事务，并关闭持久化接口对象
		session.getTransaction().commit();
		session.close();
	}

结果：

    总结：执行级联删除的时候（双向设置级联.all），执行删除某一个元素，只会删除该元素在其本身表中的数据和中间表中的级联数据。