Hibernate单向多对一级联删除引发的问题

浏览数：16 / 时间：2015年06月20日

Hibernate单向多对一在级联删除时，会出现一些问题。

下面模拟我遇到的问题：

这次模拟与之前的一次模拟方法一直，博客：http://blog.csdn.net/openjdk8/article/details/38424403

模拟场景：有一个部门表t_dept,职位表t_position。

需求：当删除部门表时，不管职位表有没数据，照样删除。删除职位表就直接删除。

1，建表：

建表：

t_dept::部门表

t_position:职位表

CREATE TABLE t_dept(
   dept_id INT PRIMARY KEY auto_increment ,   #部门Id
   dept_name VARCHAR(45)                      #部门名字
) ;

CREATE TABLE t_position(
   position_id INT PRIMARY KEY auto_increment ,   #职位Id
   position_name VARCHAR(45) ,                    #职位名字
   dept_id INT ,                                  #外键
   CONSTRAINT fk_dept_position FOREIGN KEY(dept_id) REFERENCES t_dept(dept_id) 
) ;

2，实体类(采用单向多对一)：

Dept.java

package org.jian.domain;

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

import org.hibernate.annotations.GenericGenerator;

@Entity
@Table(name = "t_dept")
public class Dept {
	private int id;
	private String name;

	@Id
	@GenericGenerator(name = "generator", strategy = "increment")
	@GeneratedValue(generator = "generator")
	@Column(name="dept_id")
	public int getId() {
		return id;
	}

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

	@Column(name="dept_name")
	public String getName() {
		return name;
	}

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

}

Position.java

package org.jian.domain;

import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import javax.persistence.Table;

import org.hibernate.annotations.GenericGenerator;

@Entity
@Table(name = "t_position")
public class Position {
	private int id;
	private String name;
	private Dept dept;


	@Id
	@GenericGenerator(name = "generator", strategy = "increment")
	@GeneratedValue(generator = "generator")
	@Column(name="position_id")
	public int getId() {
		return id;
	}

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

	@Column(name="position_name")
	public String getName() {
		return name;
	}

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

	@ManyToOne(targetEntity = Dept.class, fetch = FetchType.LAZY, cascade = { CascadeType.ALL })
	@JoinColumn(name = "dept_id")  
	public Dept getDept() {
		return dept;
	}

	public void setDept(Dept dept) {
		this.dept = dept;
	}

}

3,测试类：

package org.jian.domain;


import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.AnnotationConfiguration;
import org.junit.AfterClass;
import org.junit.BeforeClass;
import org.junit.Test;

public class DeptTest {
private static SessionFactory sf ;
	
    @BeforeClass
    public static void beforeClass(){
    	sf = new AnnotationConfiguration().configure().buildSessionFactory() ;
    }
	
    @AfterClass
    public static void afterClass(){
    	sf.close(); 
    }
    
    /**
     * 系统初始化，添加数据
     * 软件部：架构师，软件工程师，程序员
     * 财务部：会计
     * 人事部：无数据
     */
    @Test
    public void testInit(){
    	Session session = sf.openSession() ;
    	Transaction tx = session.beginTransaction() ;
    	
    	Dept d1 = new Dept() ;
    	d1.setName("软件部");
    	Dept d2 = new Dept() ;
    	d2.setName("财务部");
    	Dept d3 = new Dept() ;
    	d3.setName("人事部");
    	
    	Position p1 = new Position() ;
    	p1.setName("架构师");
    	p1.setDept(d1);
    	Position p2 = new Position() ;
    	p2.setName("软件工程师");
    	p2.setDept(d1);
    	Position p3 = new Position() ;
    	p3.setName("程序员");
    	p3.setDept(d1);
    	Position p4 = new Position() ;
    	p4.setName("会计");
        p4.setDept(d2);
    	
        session.save(d1) ;
        session.save(d2) ;
        session.save(d3) ;
        
        session.save(p1) ;
        session.save(p2) ;
        session.save(p3) ;
        session.save(p4) ;
        
    	tx.commit();
    	session.close() ;
    }
    
    /**
     * 我们尝试删除有数据的软件部
     */
    @Test
    public void testDelDept1(){
    	Session session = sf.openSession() ;
    	Transaction tx = session.beginTransaction() ;
    	
    	Dept dept = (Dept)session.get(Dept.class, 1) ;
    	
    	session.delete(dept);
    	
    	tx.commit();
    	session.close() ;
    }
    
    /**
     * 测试只删除职位(程序员)不删除部门
     */
    @Test
    public void testDelDept2(){
    	Session session = sf.openSession() ;
    	Transaction tx = session.beginTransaction() ;
    	
    	Position position = (Position)session.get(Position.class, 3) ;//程序员ID为3
    	
    	session.delete(position);
    	
    	tx.commit();
    	session.close() ;
    }
    
  
}

测试第一个方法，看到绿条，控制台输出：

Hibernate: select max(dept_id) from t_dept
Hibernate: select max(position_id) from t_position
Hibernate: insert into t_dept (dept_name, dept_id) values (?, ?)
Hibernate: insert into t_dept (dept_name, dept_id) values (?, ?)
Hibernate: insert into t_dept (dept_name, dept_id) values (?, ?)
Hibernate: insert into t_position (dept_id, position_name, position_id) values (?, ?, ?)
Hibernate: insert into t_position (dept_id, position_name, position_id) values (?, ?, ?)
Hibernate: insert into t_position (dept_id, position_name, position_id) values (?, ?, ?)
Hibernate: insert into t_position (dept_id, position_name, position_id) values (?, ?, ?)

Mysql生成的表：

测试testDelDept1()方法，看到了一个恶心的红条，并且报错了，控制台输出和Junit如下所示：

Hibernate: select dept0_.dept_id as dept1_0_0_, dept0_.dept_name as dept2_0_0_ from t_dept dept0_ where dept0_.dept_id=?
Hibernate: delete from t_dept where dept_id=?

测试testDelDept2()方法同样如此，

Hibernate: select position0_.position_id as position1_1_0_, position0_.dept_id as dept3_1_0_, position0_.position_name as position2_1_0_ from t_position position0_ where position0_.position_id=?
Hibernate: select dept0_.dept_id as dept1_0_0_, dept0_.dept_name as dept2_0_0_ from t_dept dept0_ where dept0_.dept_id=?
Hibernate: delete from t_position where position_id=?
Hibernate: delete from t_dept where dept_id=?

当我把Position.java里面的：

@ManyToOne(targetEntity = Dept.class, fetch = FetchType.LAZY, cascade = { CascadeType.ALL })

改为：

@ManyToOne(targetEntity = Dept.class, fetch = FetchType.LAZY)

时，没有报错，可以成功删除执行了下面语句。

Hibernate: select position0_.position_id as position1_1_0_, position0_.dept_id as dept3_1_0_, position0_.position_name as position2_1_0_ from t_position position0_ where position0_.position_id=?
Hibernate: delete from t_position where position_id=?

从上面我们可以猜测，cascade配置在哪一方配置，那么那个实体类进行操作时，会执行级联的更新或者是删除。

为了解决这个问题，我上网查了很多资料，最后尝试了一个办法，那就是使用双向多对一来配置。

这样我们就需要改一下Dept.java类了：

package org.jian.domain;

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

import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.OneToMany;
import javax.persistence.Table;

import org.hibernate.annotations.GenericGenerator;

@Entity
@Table(name = "t_dept")
public class Dept {
    private int id;
    private String name;
    private Set<Position> positions = new HashSet<Position>() ;

    @Id
    @GenericGenerator(name = "generator", strategy = "increment")
    @GeneratedValue(generator = "generator")
    @Column(name="dept_id")
    public int getId() {
        return id;
    }

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

    @Column(name="dept_name")
    public String getName() {
        return name;
    }
    
    public void setName(String name) {
        this.name = name;
    }

    @OneToMany(mappedBy = "dept", cascade = CascadeType.ALL, fetch = FetchType.LAZY)
    public Set<Position> getPositions() {
        return positions;
    }

    public void setPositions(Set<Position> positions) {
        this.positions = positions;
    }

    
}

测试类改一下初始化的代码：

 @Test
    public void testInit(){
    	Session session = sf.openSession() ;
    	Transaction tx = session.beginTransaction() ;
    	
    	Dept d1 = new Dept() ;
    	d1.setName("软件部");
    	Dept d2 = new Dept() ;
    	d2.setName("财务部");
    	Dept d3 = new Dept() ;
    	d3.setName("人事部");
    	
    	Position p1 = new Position() ;
    	p1.setName("架构师");
    	p1.setDept(d1);
    	Position p2 = new Position() ;
    	p2.setName("软件工程师");
    	p2.setDept(d1);
    	Position p3 = new Position() ;
    	p3.setName("程序员");
    	p3.setDept(d1);
    	Position p4 = new Position() ;
    	p4.setName("会计");
        p4.setDept(d2);
    	
        d1.getPositions().add(p1) ;
        d1.getPositions().add(p2) ;
        d1.getPositions().add(p3) ;
        d2.getPositions().add(p4) ;
        
        session.save(d1) ;
        session.save(d2) ;
        session.save(d3) ;
        
        session.save(p1) ;
        session.save(p2) ;
        session.save(p3) ;
        session.save(p4) ;
        
    	tx.commit();
    	session.close() ;
    }

测试这个方法，控制台输出如下：

Hibernate: select max(dept_id) from t_dept
Hibernate: select max(position_id) from t_position
Hibernate: insert into t_dept (dept_name, dept_id) values (?, ?)
Hibernate: insert into t_position (dept_id, position_name, position_id) values (?, ?, ?)
Hibernate: insert into t_position (dept_id, position_name, position_id) values (?, ?, ?)
Hibernate: insert into t_position (dept_id, position_name, position_id) values (?, ?, ?)
Hibernate: insert into t_dept (dept_name, dept_id) values (?, ?)
Hibernate: insert into t_position (dept_id, position_name, position_id) values (?, ?, ?)
Hibernate: insert into t_dept (dept_name, dept_id) values (?, ?)

执行testDelDept1()方法，看到了绿条

Hibernate: select dept0_.dept_id as dept1_0_0_, dept0_.dept_name as dept2_0_0_ from t_dept dept0_ where dept0_.dept_id=?
Hibernate: select positions0_.dept_id as dept3_0_1_, positions0_.position_id as position1_1_, positions0_.position_id as position1_1_0_, positions0_.dept_id as dept3_1_0_, positions0_.position_name as position2_1_0_ from t_position positions0_ where positions0_.dept_id=?
Hibernate: delete from t_position where position_id=?
Hibernate: delete from t_position where position_id=?
Hibernate: delete from t_position where position_id=?
Hibernate: delete from t_dept where dept_id=?

在“一”的一方成功实现了级联删除。

重新生成表

测试testDelDept2()方法，看到了绿条,控制台输出：

Hibernate: select position0_.position_id as position1_1_0_, position0_.dept_id as dept3_1_0_, position0_.position_name as position2_1_0_ from t_position position0_ where position0_.position_id=?
Hibernate: delete from t_position where position_id=?

~综：

1，在一对多（多对一）关系中，如果某个实体类配置了cascade属性（除了设置为‘‘none"），则这个实体类将会执行级联操作。

2，如果想实现在“一”删除后，“多”的数据删除，则必须配置一对多关系。由于需求要求当查询职位时，同时返回部门，所以配置了多对一的关系。综合起来，就是多对一（一对多）双向关联。