hibernate学习(5)——多对多关系映射

1、创建实体和映射

package com.alice.hibernate03.vo;

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

public class Student {
    private Integer id;
    private String sname;
    private Set<Course> courses = new HashSet<Course>();
    public Integer getId() {
        return id;
    }
    public void setId(Integer id) {
        this.id = id;
    }
    public String getSname() {
        return sname;
    }
    public void setSname(String sname) {
        this.sname = sname;
    }
    public Set<Course> getCourses() {
        return courses;
    }
    public void setCourses(Set<Course> courses) {
        this.courses = courses;
    }
}

package com.alice.hibernate03.vo;

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

public class Course {
    private Integer id;
    private String cname;
    private Set<Student> students = new HashSet<Student>();
    public Integer getId() {
        return id;
    }
    public void setId(Integer id) {
        this.id = id;
    }
    public String getCname() {
        return cname;
    }
    public void setCname(String cname) {
        this.cname = cname;
    }
    public Set<Student> getStudents() {
        return students;
    }
    public void setStudents(Set<Student> students) {
        this.students = students;
    }
}

2、映射

<?xml version="1.0" encoding="utf-8" ?>
<!DOCTYPE hibernate-mapping PUBLIC
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="com.alice.hibernate03.vo">
     <class name="Student" table="t_student">
        <id name="id" column="id">
           <generator class="native"></generator>
        </id>
        <property name="sname" column="sname" type="string"></property>
        <!-- 多对多关系 -->
        <!--
            set 表达集合
                name: 集合的属性名
                table:多对多中间表的表名
            key 表达外键
                column:引用我的外键名
            many-to-many 表达多对多
                class : 集合引用方的类型
                column:对方在中间表的外键名
         -->
        <set name="courses" table="t_student_course" inverse="false" cascade="save-update">
        <!--
                 key 用来描述外键
                 column : 外键的值
               -->
          <key column="sid"></key>
          <many-to-many class="Course" column="cid"></many-to-many>
        </set>
     </class>
</hibernate-mapping>

<?xml version="1.0" encoding="utf-8" ?>
<!DOCTYPE hibernate-mapping PUBLIC
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="com.alice.hibernate03.vo">
     <class name="Course" table="t_course">
        <id name="id" column="id">
           <generator class="native"></generator>
        </id>
        <property name="cname" column="cname" type="string"></property>
        <!-- 多对多关系 -->
		<!--
			set 表达集合
				name: 集合的属性名
				table:多对多中间表的表名
			key 表达外键
				column:引用我的外键名
			many-to-many 表达多对多
				class : 集合引用方的类型
				column:对方在中间表的外键名
		 -->
        <set name="students" table="t_student_course" inverse="true" cascade="save-update">
          <key column="cid"></key>
          <many-to-many class="Student" column="sid"></many-to-many>
        </set>
     </class>
</hibernate-mapping>

　　3、测试

package com.alice.hibernate03.many;

import org.hibernate.Session;
import org.hibernate.Transaction;
import org.junit.Test;

import com.alice.hibernate03.util.HibernateUtil;
import com.alice.hibernate03.vo.Course;
import com.alice.hibernate03.vo.Student;

public class ManyTest {
    @Test
    public void test01(){
        //保存学生 => 通过学生保存课程. 由学生维护外键
        //Student 的
            //inverse =  false
            //cascade =  save-update
        //Course
            //inverse = true
        Session session = HibernateUtil.openSession();
        Transaction tran = session.beginTransaction();
        //...........................
        Student s1 = new Student();
        s1.setSname("angle");

        Student s2 = new Student();
        s2.setSname("echo");

        Course c1 = new Course();
        c1.setCname("jdbc");

        Course c2 = new Course();
        c2.setCname("spring");

        Course c3 = new Course();
        c3.setCname("strust2");

        s1.getCourses().add(c1);
        s1.getCourses().add(c2);

        s2.getCourses().add(c2);
        s2.getCourses().add(c3);

        session.save(s1);
        session.save(s2);
        //...........................
        tran.commit();
        session.close();
    }
}