Hibernate中map的研究：多對多

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Teacher.java

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package blog.hibernate.domain;

import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class Teacher {

    private int id;
    private String name;
    private String course;

    private Map<String, Student> students = new HashMap<String, Student>();

    public Map<String, Student> getStudents() {
        return students;
    }

    public void setStudents(Map<String, Student> students) {
        this.students = students;
    }

    
    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
    
     public String getCourse() {
        return course;
    }

    public void setCourse(String course) {
        this.course = course;
    }

    @Override
    public String toString() {
        return "Teacher{" + "id=" + id + ", name=" + name + ", course=" + course + '}';
    }
}

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Teacher.hbm.xml

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<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
        "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping package="blog.hibernate.domain">
	<class name="Teacher" table="teachers">
		<id name="id" column="teacher_id">
			<generator class="native"></generator>
		</id>
		<property name="name" column="teacher_name"></property>
		<property name="course"></property>
		
                  <map name="students" table="teacher_student" inverse="true">
                    <key column="teacher_id" />
                    <index column="Course" type="string"/>
                    <many-to-many class="Student" column="student_id"/>
                  </map>
	</class>
</hibernate-mapping>

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Student.java

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package blog.hibernate.domain;

import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class Student {

    private int id;
    private String name;
    private Map<String, Teacher> teachers = new HashMap<String, Teacher>();

    public Map<String, Teacher> getTeachers() {
        return teachers;
    }

    public void setTeachers(Map<String, Teacher> teachers) {
        this.teachers = teachers;
    }
    
    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @Override
    public String toString() {
        return "Student{" + "id=" + id + ", name=" + name + '}';
    }
}

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Student.hbm.xml

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<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
        "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping package="blog.hibernate.domain">
	<class name="Student" table="students">
		<id name="id" column="student_id">
			<generator class="native"></generator>
		</id>
		<property name="name" column="student_name"></property>
                 
                 <map name="teachers" table="teacher_student">
                       <key column="student_id"/>
                       <index column="Course" type="string"/>
                       <many-to-many class="Teacher" column="teacher_id"/>
                 </map>
	</class>
</hibernate-mapping>

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hibernate.cfg.xml

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<?xml version='1.0' encoding='utf-8'?>
<!DOCTYPE hibernate-configuration PUBLIC
    "-//Hibernate/Hibernate Configuration DTD//EN"
    "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">

<hibernate-configuration>
    <session-factory>
        <property name="hibernate.connection.driver_class">org.gjt.mm.mysql.Driver</property>
        <property name="hibernate.connection.url">jdbc:mysql://localhost:3306/hibernate</property><!-- ///表示連接本機的數據庫//localhost:3306 -->
        <property name="hibernate.connection.username">root</property>
        <property name="hibernate.connection.password">1234</property>
        <property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>
   		
        <property name="hibernate.hbm2ddl.auto">create</property>
        <property name="hibernate.show_sql">true</property>
                
        <mapping resource="blog/hibernate/domain/Student.hbm.xml"/>
        <mapping resource="blog/hibernate/domain/Teacher.hbm.xml"/>
 
    </session-factory>	
</hibernate-configuration>

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junit test

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package juint.test;

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

import blog.hibernate.HibernateUtil;
import blog.hibernate.domain.Student;
import blog.hibernate.domain.Teacher;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.logging.Level;
import java.util.logging.Logger;

public class Many2Many {

    @BeforeClass
    public static void setUpBeforeClass() throws Exception {
    }

    @Test
    public void test() {
        map_add();
    }

    public void map_add() {
        Teacher t1 = new Teacher();
        t1.setName("t1");
        t1.setCourse("Math");

        Teacher t2 = new Teacher();
        t2.setName("t2");
        t2.setCourse("English");


        Student s1 = new Student();
        s1.setName("s1");

        Student s2 = new Student();
        s2.setName("s2");

        /**
         * 第一種方法
         */
        Map<String, Teacher> teachers = new HashMap<String, Teacher>();
        teachers.put("Math", t1);
        teachers.put("English", t2);

        s1.setTeachers(teachers);
        s2.setTeachers(teachers);

        /**
         * 第二種方法
         */
//                s1.getTeachers().put("Math", t1);
//                s1.getTeachers().put("English", t2);
//                
//                s2.getTeachers().put("Math", t1);
//                s2.getTeachers().put("English", t2);
        Session session = null;
        Transaction tx = null;
        try {
            session = HibernateUtil.getSession();
            tx = session.beginTransaction();
            session.save(s1);
            session.save(s2);
            session.save(t1);
            session.save(t2);
            tx.commit();
        } catch (Exception e) {
            Logger.getLogger(Many2Many.class.getName()).log(Level.SEVERE, null, e);
            if (tx != null) {
                tx.rollback();
            }
        } finally {
            if (session != null) {
                session.close();
            }
        }
    }
}