jpa级联操作详解2--级联删除(CascadeType.REMOVE)

Garage.java
Java代码 收藏代码

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;  @Entity  public class Garage {      /**      * many to one 多对一      */      private Integer gid;      private String garagenum;      private Set<Auto> autos = new HashSet<Auto>();      @Id @GeneratedValue      public 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
Java代码 收藏代码

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;  @Entity  public class Auto {      /**      * one to many 一对多关联      */      private Integer autoId;      private String autotype;      private String autonum;      private Garage garage;      @Id @GeneratedValue      public 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()
Java代码 收藏代码

@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 transactionCaused 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：
C#代码 收藏代码

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
Java代码 收藏代码

@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
Sql代码 收藏代码

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 收藏代码

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

Sql代码 收藏代码

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？