基于Annotation 的多对一ManyToOne双向和基于XML配置多对一双向

转自:http://stark-summer.iteye.com/blog/840712

基于Annotation：

package com.stark.hibernate.model;

import java.util.HashSet;

import java.util.Set;

import javax.persistence.CascadeType;

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 groupId ;

private String groupName;

private Set<User> users= new HashSet<User>();

@Id

@GeneratedValue

public int getGroupId() {

return groupId;

}

public void setGroupId(int id) {

this.groupId = id;

}

public String getGroupName() {

return groupName;

}

public void setGroupName(String name) {

this.groupName = name;

}

/**

* One 代表Group，Many代表User ,我们需要在多的一方添加外键，如果不添加@JoinColumn(name="groupId")，将会生成一张t_group_t_user的中间表

* 否则将会在user表中自动添加groupId字段

* @return

*/

@OneToMany(mappedBy="group",cascade = { CascadeType.ALL})

@JoinColumn(name="groupId")

public Set<User> getUsers() {

return users;

}

public void setUsers(Set<User> users) {

this.users = users;

}

}

PS：需要在Group表中添加OneToMany(mappedBy="group"),目的就是外键由User表来指定，如果不添加，将会在User中自动添加一条t_group_id,这是冗余字段的

package com.stark.hibernate.model;

import javax.persistence.Entity;

import javax.persistence.GeneratedValue;

import javax.persistence.Id;

import javax.persistence.JoinColumn;

import javax.persistence.ManyToOne;

import javax.persistence.Table;

@Entity

@Table(name="t_user")

public class User {

private int userId;

private String userName;

private Group group;

@Id

@GeneratedValue

public int getUserId() {

return userId;

}

public void setUserId(int userId) {

this.userId = userId;

}

public String getUserName() {

return userName;

}

public void setUserName(String userName) {

this.userName = userName;

}

/**

*

* 只需在多方User中添加一个Group同时添加注解@ManyToOne即可（Many代表User，One代表Group）

*/

@ManyToOne

@JoinColumn(name="groupId")

public Group getGroup() {

return group;

}

public void setGroup(Group group) {

this.group = group;

}

}

生成DDL语句为：

create table t_group (groupId integer not null auto_increment, groupName varchar(255), primary key (groupId))

create table t_user (userId integer not null auto_increment, userName varchar(255), groupId integer, primary key (userId))

alter table t_user add index FKCB63CCB65F00FCD6 (groupId), add constraint FKCB63CCB65F00FCD6 foreign key (groupId) references t_group (groupId)

基于XML:

去掉Group和UserJavaBean中所有@注解

Group.hbm.xml:

<?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="com.stark.hibernate.model">

<class name="Group" table="t_group">

<id name="groupId" >

<generator class="native"/>

</id>

<property name="groupName"/>

<set name="users">

<key column="groupId"></key>

<one-to-many class="User"/>

</set>

</class>

</hibernate-mapping>

User.hml.xml:

<?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="com.stark.hibernate.model">

<class name="User" table="t_user">

<id name="userId">

<generator class="native"/>

</id>

<property name="userName" />

<many-to-one name="group" column="groupId" cascade="all" ></many-to-one>

</class>

</hibernate-mapping>

生成DDL语句：

与用Annotation生成的是一样的。