hibernate----one-to-many

最新推荐文章于 2020-03-24 15:24:20 发布

最新推荐文章于 2020-03-24 15:24:20 发布 · 167 阅读

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#Hibernate #Java #Apache #Struts #SQL

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本文介绍Hibernate框架中一对多关联的实现方式，包括双向关联和单向关联两种情况，并通过具体的学生和班级实例来演示如何进行数据的保存、修改及查询。

hibernate里的一对多one-to-many(以学生和班级为例子)
[color=red]1.双向关联情况下[/color]

Classes.java:


package com.domain;

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

public class Classes implements java.io.Serializable {


	private Integer id;

	private String name;

	private Set students = new HashSet(0);

	public Classes() {
	}

	public Classes(String name) {
		this.name = name;
	}

	public Classes(String name, Set students) {
		this.name = name;
		this.students = students;
	}

	public Integer getId() {
		return this.id;
	}

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

	public String getName() {
		return this.name;
	}

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

	public Set getStudents() {
		return this.students;
	}

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

}

Student.java



package com.domain;

public class Student implements java.io.Serializable {

	private Integer id;

	private Classes classes;

	private String name;

	public Student() {
	}

	public Student(String name) {
		this.name = name;
	}

	public Student(Classes classes, String name) {
		this.classes = classes;
		this.name = name;
	}

	public Integer getId() {
		return this.id;
	}

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

	public Classes getClasses() {
		return this.classes;
	}

	public void setClasses(Classes classes) {
		this.classes = classes;
	}

	public String getName() {
		return this.name;
	}

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

}

Classes.hbm.xml



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

<hibernate-mapping>
    <class name="com.domain.Classes" table="classes" catalog="hibernatetest">
        <id name="id" type="java.lang.Integer">
            <column name="id" />
            <generator class="native" />
        </id>
        <property name="name" type="java.lang.String">
            <column name="name" not-null="true" />
        </property>
        <!-- inverse="true" 主动权反转给了Classes,cascade="all"级联students表里的数据会级联被删除或更新等，这里设置的是all,lazy="true" students表里的数据会lazy加载 -->
        <set name="students" inverse="true" cascade="all" lazy="true">
            <key>
                <column name="classId" />
            </key>
            <one-to-many class="com.domain.Student" />
        </set>
    </class>
</hibernate-mapping>

Student.hbm.xml




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

<hibernate-mapping>
    <class name="com.domain.Student" table="student" catalog="hibernatetest">
        <id name="id" type="java.lang.Integer">
            <column name="id" />
            <generator class="native" />
        </id>
        <!-- cascade="all" classes表里的数据会被级联操作   fetch="select" classes表里的数据会以左外连接的形式取出来（根据学生查找班级的具体信息时），如果值是join 则进行内连接-->
        <many-to-one name="classes" class="com.domain.Classes" fetch="select" cascade="all">
            <column name="classId" />
        </many-to-one>
        <property name="name" type="java.lang.String">
            <column name="name" not-null="true" />
        </property>
    </class>
</hibernate-mapping>

测试类


package com.dao;


import java.util.Iterator;
import java.util.Set;

import org.hibernate.Hibernate;
import org.hibernate.Query;
import org.hibernate.Session;
import org.hibernate.Transaction;

import com.domain.Classes;
import com.domain.Student;

public class Test {
	public static void main(String[] args){
		Session session = HibernateSessionFactory.getSession();
		Transaction tx = session.beginTransaction();
		//添加数据
		/*

		//定义学生一
		Student student1 = new Student();
		student1.setName("zhansan");
		//定义学生二
		Student student2 = new Student();
		student2.setName("lisi");

		//定义班级0201班
		Classes classes = new Classes();
		classes.setName("0201");
		//双向关联给主表设置关联
		classes.getStudents().add(student1);
		classes.getStudents().add(student2);

		//双向关联给从表设置关联
		student1.setClasses(classes);
		student2.setClasses(classes);

		session.save(classes);

		tx.commit();
		session.close();
		*/

		//修改多方
		//修改学生，必须给要修改的这个学生每个属性都赋值
		/*Student student = new Student();
		student.setName("wangwu111");
		student.setId(1);

		Classes classes = new Classes();
		classes.setId(1);
		classes.setName("0201");
		//如果下面这句代码不要的话，则修改执行的sql为update hibernatetest.student set classId=?, name=? where id=?，修改后classId为null(即使classId原来有值，也会被改为null)，所以，必须给要修改的这个学生每个属性都赋值
		student.setClasses(classes);

		//修改
		session.update(student);

		tx.commit();
		session.close();*/
		//修改执行的sql:
		/*
		Hibernate: update hibernatetest.student set classId=?, name=? where id=?
		Hibernate: update hibernatetest.classes set name=? where id=?
		级联修改
		*/



		//修改一方,不需要给Set集合属性赋值
		/*
		Classes classes = new Classes();
		classes.setId(1);
		classes.setName("0210");
		//修改
		session.update(classes);

		tx.commit();
		session.close();*/
		//执行的sql:Hibernate: update hibernatetest.classes set name=? where id=?

		//查询操作
		String hql = "from Classes c where c.id=1";
		Query query = session.createQuery(hql);
		Classes classes = (Classes)query.uniqueResult();
		System.out.println(classes.getId() + " : " + classes.getName() + " : ");
		//如果再这里进行session.close();那么需要写下面的判断,强制性去拿student表里的数据
//		if(!Hibernate.isInitialized(classes.getStudents())){
//			Hibernate.initialize(classes.getStudents());
//		}

		//因为Student设置的lazy,执行下面的语句时，才去student表查询
		Set set = classes.getStudents();
		Iterator iterator = set.iterator();
		while(iterator.hasNext()){
			Student cla = (Student)iterator.next();
			System.out.println(cla.getId() + " : " + cla.getName());
		}
		session.close();
		//执行的sql
		/*
		Hibernate: select classes0_.id as id1_, classes0_.name as name1_ from hibernatetest.classes classes0_ where classes0_.id=1
		1 : 0210 : 
		Hibernate: select students0_.classId as classId1_, students0_.id as id1_, students0_.id as id0_0_, students0_.classId as classId0_0_, students0_.name as name0_0_ from hibernatetest.student students0_ where students0_.classId=?
		2 : zhansan
		1 : wangwu111
		*/
	}

}

根据学生查找班级：



package com.dao;

import java.util.List;

import org.hibernate.Query;
import org.hibernate.Session;

import com.domain.Student;

public class TestSelect {

	public static void main(String[] args) {
		Session session = HibernateSessionFactory.getSession();
		String hql = "from Student s where s.classes.id=1";
		Query query = session.createQuery(hql);
		List<Student> list = query.list();

		for(int i=0;i<list.size();i++){
			Student student = (Student)list.get(i);
			System.out.println(student.getId() + " : " + student.getName() + " : " + student.getClasses().getId() + " : " + student.getClasses().getName());

			//执行的sql:Hibernate: select student0_.id as id0_, student0_.classId as classId0_, student0_.name as name0_ from hibernatetest.student student0_ where student0_.classId=1
			//System.out.println(student.getId() + " : " + student.getName());
		}

		session.close();
		/**
		 执行的sql为：
		 Hibernate: select student0_.id as id0_, student0_.classId as classId0_, student0_.name as name0_ from hibernatetest.student student0_ where student0_.classId=1
		 Hibernate: select classes0_.id as id1_0_, classes0_.name as name1_0_ from hibernatetest.classes classes0_ where classes0_.id=?



		 */

	}

}

[color=red]2.单向关联情况下[/color]

把一方的Set集合去掉，对应的.hbm.xml里的部分也给去掉。
即去掉：


 <set name="students" inverse="true" cascade="all" lazy="true">
            <key>
                <column name="classId" />
            </key>
            <one-to-many class="com.domain.Student" />
        </set>

测试类：


package com.dao;

import org.hibernate.Session;
import org.hibernate.Transaction;

import com.domain.Classes;
import com.domain.Student;

public class TestInsert {

	public static void main(String[] args) {
		Session session = HibernateSessionFactory.getSession();
		Transaction tx = session.beginTransaction();
		//定义班级0201班
		Classes classes = new Classes();
		classes.setName("0201test");

		//定义学生一
		Student student1 = new Student();
		student1.setName("zhansantest");
		student1.setClasses(classes);
		//定义学生二
		Student student2 = new Student();
		student2.setName("lisitest");
		student2.setClasses(classes);

		//classes一定要最先被save
		session.save(classes);
		session.save(student1);
		session.save(student2);

		tx.commit();
		session.close();
		/**
		 执行的sql:
		 Hibernate: insert into hibernatetest.classes (name) values (?)
		 Hibernate: insert into hibernatetest.student (classId, name) values (?, ?)
		 Hibernate: insert into hibernatetest.student (classId, name) values (?, ?)
		 */




	}

}