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

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。