jpa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;
@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

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()

@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

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

 

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？