Hibernate单向多对一级联删除引发的问题
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() ;
}
}
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 positions = new HashSet() ;
@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 getPositions() {
return positions;
}
public void setPositions(Set 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=?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。