hibernate（七）组件映射与多对一映射

一、组件映射

用注解配置组件映射：

Husband为我们映射的类，wife是这个类的一部分(属性不能与husband中属性重名，不要写Entity注解，不要有主键)

Husband类：(在getWife()方法上添加注解@Embedded)

package cn.orlion.hibernate.model;

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

@Entity
public class Husband {
    
    private int id;
    
    private String name;
    
    private Wife wife;
    
    @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;
    }
    @Embedded
    public Wife getWife() {
        return wife;
    }

    public void setWife(Wife wife) {
        this.wife = wife;
    }
}

wife类：

package cn.orlion.hibernate.model;

public class Wife {
    
    private String wifename;

    public String getWifename() {
        return wifename;
    }

    public void setWifename(String wifename) {
        this.wifename = wifename;
    }

}

建表语句：

create table Husband (
        id integer not null auto_increment,
        name varchar(255),
        wifename varchar(255),
        primary key (id)
    )

二、多对一映射

1、多对一单向映射

注解方式配置：（一个组有多个用户，每个用户对应一个组,user是多的一方，group是一）

Group类：

package cn.orlion.hibernate.model;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.Table;
/*
 * 一个组有多个用户，每个用户对应一个组,user是多的一方，group是一
 */
@Entity
@Table(name="t_group")
public class Group {

    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;
    }
}

User类：

package cn.orlion.hibernate.model;

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;
    
    private Group group;
    @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;
    }
    @ManyToOne
    public Group getGroup() {
        return group;
    }

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

hibernate生成的sql:

create table t_group (
        id integer not null auto_increment,
        name varchar(255),
        primary key (id)
    )

create table t_user (
        id integer not null auto_increment,
        name varchar(255),
        group_id integer,
        primary key (id)
    )

alter table t_user 
        add constraint FK_e5f24mh6aryt9hsy99oydps6g 
        foreign key (group_id) 
        references t_group (id)