【hibernate框架】多对一单向关联(Annotation实现)

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光仔December 2023-03-18 10:03:25 ©著作权

文章标签 JAVA hibernate 数据库多对一单向关联 Annotation 文章分类 JavaScript 前端开发

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一个组有多个用户，一个用户只能属于一个组。
使用Annotation注解来实现多对一单项关联

Group.java:

package cn.edu.hpu.many2one;


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 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.java:

package cn.edu.hpu.many2one;


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;
  
  @ManyToOne //核心语句
  //@JoinColumn(name="groupid")想改属性名用这个(默认的是group_id)
  public Group getGroup() {
    return group;
  }
  public void setGroup(Group group) {
    this.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;
  }
  
}

在hibernate.cfg.xml中配置：

<mapping class="cn.edu.hpu.many2one.Group"/>
<mapping class="cn.edu.hpu.many2one.User"/>

建表语句：

alter table t_user 

         drop 

         foreign key FKCB63CCB61AEE691B



     drop table if exists t_group



     drop table if exists t_user



     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 index FKCB63CCB61AEE691B (group_id), 

         add constraint FKCB63CCB61AEE691B 

         foreign key (group_id) 

         references t_group (id)

 schema export complete