多对一（一对多）的双向关联

一个组（Group）有多个用户（User），进行多对一（一对多）的双向配置，在数据库中生成的表结构如下图：

　　Annotation配置：

　　　　　　Group:

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.OneToMany;
import javax.persistence.Table;

@Entity
@Table(name="t_group")
public class Group {
    private Integer id;
    
    private String name;
    
    private Set<User> users = new HashSet<User>();

    @Id
    @GeneratedValue
    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @OneToMany(mappedBy="group")//表示和User是一对多的关系，并且以User的group属性为准，自己就不做映射配置了
    public Set<User> getUsers() {
        return users;
    }

    public void setUsers(Set<User> users) {
        this.users = users;
    }
}

　　　　　　User:

package com.bjsxt.hibernate;

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 Integer id;
    
    private String name;
    
    private Group group;
    
    @Id
    @GeneratedValue
    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @ManyToOne
    @JoinColumn(name="group_ID")//指定列名为 group_ID
    public Group getGroup() {
        return group;
    }

    public void setGroup(Group group) {
        this.group = group;
    }
}

　　　　XML 配置：

　　　　　　Group:

package com.bjsxt.hibernate;

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

public class Group {
    private Integer id;
    
    private String name;
    
    private Set<User> users = new HashSet<User>();

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Set<User> getUsers() {
        return users;
    }

    public void setUsers(Set<User> users) {
        this.users = users;
    }
}

　　　　　　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.bjsxt.hibernate">
    <class name="Group" table="t_group">
        <id name="id" column="id">
            <generator class="native"/>
        </id>
        <property name="name" column="name" />
        <set name="users">
            <key column="groupId"></key>
            <one-to-many class="User"/>
        </set>
    </class>
</hibernate-mapping>

　　　　　　User:

package com.bjsxt.hibernate;

public class User {
    private Integer id;
    
    private String name;
    
    private Group group;
    
    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Group getGroup() {
        return group;
    }

    public void setGroup(Group group) {
        this.group = group;
    }
}

　　　　　　User.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.bjsxt.hibernate">
    <class name="User" table="t_user">
        <id name="id" column="id">
            <generator class="native"/>
        </id>
        <property name="name" column="name" />
        <many-to-one name="group" column="groupId"></many-to-one>
    </class>
</hibernate-mapping>

　　　　两个配置文件的 groupId 必须取名一致，否则会出现两个外键。

两种方式最后生成的SQL语句：

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