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>

巴特西

hibernate--一对多单向关联 (重点!!!)

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