第九章 关系映射 多对多关联映射

表设计:

有一张中间表，中间表中有两张关联表的外键

如：student与teacher

Student:

package cn.framelife.mvc.entity;

import java.util.Set;

public class Student {
	private Integer id;
	private String name;
	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 Set<Teacher> getTeachers() {
		return teachers;
	}

	public void setTeachers(Set<Teacher> teachers) {
		this.teachers = teachers;
	}
}

Teacher:

package cn.framelife.mvc.entity;

import java.util.Set;

public class Teacher {
	private Integer id;
	private String name;
	private Set<Student> 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;
	}

	public Set<Student> getStudents() {
		return students;
	}

	public void setStudents(Set<Student> students) {
		this.students = students;
	}

}

Student.hbm.xml:

<hibernate-mapping>
    <class name="cn.framelife.hibernate.entity.Student" table="student">
        <id name="id" type="java.lang.Integer">
            <column name="id" />
            <generator class="native" />
        </id>
        <property name="name" type="java.lang.String">
            <column name="s_name" length="45" not-null="true" />
        </property>
        <set name="teachers" table="s_t" cascade="all">
        	<key column="student_id"/>
        	<many-to-many column="teacher_id" class="cn.framelife.hibernate.entity.Teacher"></many-to-many>
        </set>
    </class>
</hibernate-mapping>

Teacher.hbm.xml:

<hibernate-mapping>
    <class name="cn.framelife.hibernate.entity.Teacher" table="teacher" catalog="hibernate">
        <id name="id" type="java.lang.Integer">
            <column name="id" />
            <generator class="native" />
        </id>
        <property name="name" type="java.lang.String">
            <column name="t_name" length="45" not-null="true" />
        </property>
        <set name="students" table="s_t" >
        	<key column="teacher_id"/>
        	<many-to-many column="student_id" class="cn.framelife.hibernate.entity.Student"></many-to-many>
        </set>
    </class>
</hibernate-mapping>

增加：

Student s1 = new Student();
			s1.setName("s10");
			Student s2 = new Student();
			s2.setName("s11");
			
			Set<Teacher> set = new HashSet<Teacher>();
			Teacher t1 = new Teacher();
			t1.setName("t10");
			Teacher t2 = new Teacher();
			t2.setName("t11");
			set.add(t1);
			set.add(t2);
			
			//设置学生与老师的的关系
			s1.setTeachers(set);
			s2.setTeachers(set);
			
			//增加两个学生，同时会把老师也加到数据库中
			session.save(s1);
			session.save(s2);