多对一的单向关联

多对一与一对多
1.多对一单向关联
a) 项目名称：
b) 数据库表设计：在多方加外键
c) annotation:@Many2One
d) xml:<many-to-one>

多对一：从多配置到一

案例：一个组（Group）有多个用户（User），配置从User到Group的多对一的单向关联

　　Annotation:

　　　　Group类:

package com.bjsxt.hibernate;

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

@Entity
@Table(name="t_group")
public class Group {
    private Integer id;
    
    private String name;

    @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;
    }
}

　　　　User 类：

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="groupId")//设置列的名称，可以不写，默认为group_id
    public Group getGroup() {
        return group;
    }

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

　　XML 配置：

　　　　Group:

package com.bjsxt.hibernate;

public class Group {
    private Integer id;
    
    private String name;

    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;
    }
}

　　　　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" />
    </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" />
    </class>
</hibernate-mapping>

上面两种配置的效果一样：

jar包链接: https://pan.baidu.com/s/1qY356PY 密码: bm8f

代码链接: https://pan.baidu.com/s/1o7F4HIE 密码: ap4m