Hibernate-------集合

Hibernate中的集合
Hibernate中的集合分为四类:
1.bag类:元素无序，可重复
2.set类:元素无序,不可重复
3.list类:元素有序，可重复
4.array类:数组
5.map类:映射关系
除bag类集合外，其它集合都可以在java api中找到对应的接口类，bag可以认为对应java中的List
Hibernate中将集合分为2类：
一是值集合，集合中存储的都是基本数据类型，包括String类型，及其它可识别的数据库类型
二是实体集合，集合中存储已经映射了的实体对象，反应对象间的关系。

以班级和学生为例：
建表sql语句：

CREATE DATABASE `hibernatetest`
CHARACTER SET 'utf8';

USE `hibernatetest`;

DROP TABLE IF EXISTS `classes`;
CREATE TABLE `classes` (
  `id` int(11) NOT NULL auto_increment,
  `name` varchar(255) NOT NULL,
  PRIMARY KEY  (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

DROP TABLE IF EXISTS `student`;
CREATE TABLE `student` (
  `id` int(11) NOT NULL auto_increment,
  `name` varchar(255) NOT NULL,
  `classId` int(11) ,
  foreign key (`classId`) references classes(`id`),
  PRIMARY KEY  (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

Classes.java

package com.domain;

import java.util.ArrayList;
import java.util.List;

public class Classes implements java.io.Serializable {
	private Integer id;

	private String name;

	//Hibernate里的bag集合对应java里的List
	private List studentNames = new ArrayList();

	public Classes() {
	}

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


	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 List getStudentNames() {
		return studentNames;
	}

	public void setStudentNames(List studentNames) {
		this.studentNames = studentNames;
	}

}

Student.java:

package com.domain;

public class Student implements java.io.Serializable {

	private Integer id;

	private String name;

	public Student() {
	}

	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;
	}

}

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" >
        <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>
        <bag name="studentNames" table="student">
        	<!-- key对应的都是外键，其意思也就是拿该外键和<id>的主键值匹配，取集合 -->
        	<key column="classId"></key>
        	<element column="name" type="string"></element>
        </bag>
        
    </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 package="com.domain" auto-import="true">
    <class name="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="name" not-null="true" />
        </property>
    </class>
</hibernate-mapping>

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("0201new");
		classes.getStudentNames().add("studentnew1");
		classes.getStudentNames().add("studentnew2");
		session.save(classes);
		
		
		tx.commit();
		session.close();
		/**
		 执行的sql:
		 Hibernate: insert into classes (name) values (?)
		 Hibernate: insert into student (classId, name) values (?, ?)
         Hibernate: insert into student (classId, name) values (?, ?)
		 */


	}

}