JPA级联操作详解——级联删除(CascadeType.REMOVE)

Garage.java

package com.hibernate.jpa.bean1;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;@Entitypublic class Garage {/** * many to one 多对一 */private Integer gid;private String garagenum;private Set<Auto> autos = new HashSet<Auto>();@Id @GeneratedValuepublic Integer getGid() {return gid;}public void setGid(Integer gid) {this.gid = gid;}@Column(length=20)public String getGaragenum() {return garagenum;}public void setGaragenum(String garagenum) {this.garagenum = garagenum;}@OneToMany(cascade={CascadeType.PERSIST},mappedBy="garage")public Set<Auto> getAutos() {return autos;}public void setAutos(Set<Auto> autos) {this.autos = autos;}public void addGarageAuto(Auto auto) {auto.setGarage(this);this.autos.add(auto);}}

Auto.java

package com.hibernate.jpa.bean1;import javax.persistence.CascadeType;import javax.persistence.Entity;import javax.persistence.GeneratedValue;import javax.persistence.Id;import javax.persistence.JoinColumn;import javax.persistence.ManyToOne;@Entitypublic class Auto {/** * one to many 一对多关联 */private Integer autoId;private String autotype;private String autonum;private Garage garage;@Id @GeneratedValuepublic Integer getAutoId() {return autoId;}public void setAutoId(Integer autoId) {this.autoId = autoId;}public String getAutotype() {return autotype;}public void setAutotype(String autotype) {this.autotype = autotype;}public String getAutonum() {return autonum;}public void setAutonum(String autonum) {this.autonum = autonum;}@ManyToOne()@JoinColumn(name="garageid")public Garage getGarage() {return garage;}public void setGarage(Garage garage) {this.garage = garage;}}

持久化数据

mysql> select * from garage;
+-----+-----------+
| gid | garagenum |
+-----+-----------+
| 1 | room1 |
| 2 | room2 |
| 3 | room3 |
+-----+-----------+

mysql> select * from auto;
+--------+---------+----------+----------+
| autoId | autonum | autotype | garageid |
+--------+---------+----------+----------+
| 1 | hk2222 | car | 1 |
| 2 | bj0000 | car | 1 |
| 3 | jn1d31 | bus | 3 |
| 4 | sh3243 | car | 3 |
+--------+---------+----------+----------+

junit测试方法delete()

@Test public void delete() {EntityManagerFactory factory = Persistence.createEntityManagerFactory("jpa-hibernate");EntityManager em = factory.createEntityManager();em.getTransaction().begin();Garage garage = em.find(Garage.class, 3);em.remove(garage);em.getTransaction().commit();em.close();factory.close();}

调用delete方法是myeclipse控制台出现异常

javax.persistence.RollbackException: Error while commiting the transaction

Caused by: java.sql.BatchUpdateException: Cannot delete or update a parent row: a foreign key constraint fails (`itcast/auto`, CONSTRAINT `FK1F51CFA8A25FB2` FOREIGN KEY (`garageid`) REFERENCES `garage` (`gid`))

发出的sql语句是：

Hibernate: select garage0_.gid as gid1_0_, garage0_.garagenum as garagenum1_0_ from Garage garage0_ where garage0_.gid=?

二）在Garage.java中添加CascadeType.REMOVE注解

@OneToMany(cascade={CascadeType.PERSIST,CascadeType.REMOVE},mappedBy="garage")public Set<Auto> getAutos() {return autos;}

此时再次调用junit单元测试的delete方法

测试显示成功，发出的sql语句为

Hibernate: select garage0_.gid as gid1_0_, garage0_.garagenum as garagenum1_0_ from Garage garage0_ where garage0_.gid=?Hibernate: select autos0_.garageid as garageid1_, autos0_.autoId as autoId1_, autos0_.autoId as autoId0_0_, autos0_.autonum as autonum0_0_, autos0_.autotype as autotype0_0_, autos0_.garageid as garageid0_0_ from Auto autos0_ where autos0_.garageid=?Hibernate: delete from Auto where autoId=?Hibernate: delete from Auto where autoId=?Hibernate: delete from Garage where gid=?

此时表garage中的gid为3的字段被全部删除，同时也级联删除了与garage相关联表auto中garageid为3的字段

Sql代码

1. mysql> select * from garage;
2. +-----+-----------+
3. | gid | garagenum |
4. +-----+-----------+
5. | 1 | room1 |
6. | 2 | room2 |
7. +-----+-----------+

mysql> select * from garage;+-----+-----------+| gid | garagenum |+-----+-----------+|   1 | room1     ||   2 | room2     |+-----+-----------+

Sql代码

1. mysql> select * from auto;
2. +--------+---------+----------+----------+
3. | autoId | autonum | autotype | garageid |
4. +--------+---------+----------+----------+
5. | 1 | hk2222 | car | 1 |
6. | 2 | bj0000 | car | 1 |
7. +--------+---------+----------+----------+

mysql> select * from auto;+--------+---------+----------+----------+| autoId | autonum | autotype | garageid |+--------+---------+----------+----------+|      1 | hk2222  | car      |        1 ||      2 | bj0000  | car      |        1 |+--------+---------+----------+----------+

怎么样，这下级联删除也明白了吧？