hibernate--一对多单向关联 (重点!!!)

多对一是在多的类上存在一的对象

一对多是在一的类上存在多的集合.

多的类

user.java:

 package com.bjsxt.hibernate;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.ManyToOne;
import javax.persistence.Table;

@Entity
@Table(name="t_user")
public class User {
	private int id;
	private String name;

	@Id
	@GeneratedValue
	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;
	}
}

一的类Group.java, 需要多的集合:

package com.bjsxt.hibernate;

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

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.OneToMany;
import javax.persistence.Table;

@Entity
@Table(name="t_group")
public class Group {
	private int id;
	private String name;
	private Set<User> users = new HashSet<User>();
	@Id
	@GeneratedValue
	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;
	}
	@OneToMany
	@JoinColumn(name="groupId")
	public Set<User> getUsers() {
		return users;
	}
	public void setUsers(Set<User> users) {
		this.users = users;
	}
}

test文件:

package com.bjsxt.hibernate;

import java.util.Date;

import org.hibernate.Query;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.AnnotationConfiguration;
import org.hibernate.tool.hbm2ddl.SchemaExport;
import org.junit.AfterClass;
import org.junit.BeforeClass;
import org.junit.Test;

public class HibernateORMappingTest {
	private static SessionFactory sessionFactory;

	//@BeforeClass
	public static void beforeClass() {
			sessionFactory = new AnnotationConfiguration().configure().buildSessionFactory();
	}
	//@AfterClass
	public static void afterClass() {
		sessionFactory.close();
	}

	@Test
	public void testSchemaExport() {
		new SchemaExport(new AnnotationConfiguration().configure()).create(false, true);
	}

	public static void main(String[] args) {
		beforeClass();
	}
}

　　

　

运行test的结果:

14:15:34,169 DEBUG org.hibernate.tool.hbm2ddl.SchemaExport:303 -
    create table t_group (
        id integer not null auto_increment,
        name varchar(255),
        primary key (id)
    )
14:15:34,304 DEBUG org.hibernate.tool.hbm2ddl.SchemaExport:303 -
    create table t_user (
        id integer not null auto_increment,
        name varchar(255),
        groupId integer,
        primary key (id)
    )
14:15:34,409 DEBUG org.hibernate.tool.hbm2ddl.SchemaExport:303 -
    alter table t_user
        add index FKCB63CCB6C3D18669 (groupId),
        add constraint FKCB63CCB6C3D18669
        foreign key (groupId)
        references t_group (id)
14:15:34,674  INFO org.hibernate.tool.hbm2ddl.SchemaExport:196 - schema export complete

　　

XML方式:

作为多的一方user正常写成:

<?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>
	<class name="com.bjsxt.hibernate.User" table="t_user">
		<id name="id">
			<generator class="native"></generator>
		</id>

		<property name="name"></property>

    </class>

</hibernate-mapping>

一的一方 group需要写set:

<?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>
	<class name="com.bjsxt.hibernate.Group" table="t_group">
		<id name="id">
			<generator class="native"></generator>
		</id>

		<property name="name"></property>
		<set name="users">
			<key column="groupId"></key>
			<one-to-many class="com.bjsxt.hibernate.User"/>
		</set>
    </class>

</hibernate-mapping>