jpa级联操作详解1(cascade)

package com.hibernate.jpa.bean1;

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;
	}

}
------车库
package com.hibernate.jpa.bean1;

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

import javax.persistence.Column;
import javax.persistence.Entity;
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(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);
	}

}
 ---------junit保存方法
	@Test public void save() {
		EntityManagerFactory factory = Persistence.createEntityManagerFactory("jpa-hibernate");
		EntityManager em = factory.createEntityManager();
		em.getTransaction().begin();
		
		Garage garage = new Garage();
		garage.setGaragenum("room1");
		
		Auto auto1 = new Auto();
		auto1.setAutonum("bj0000");
		auto1.setAutotype("car");
		
		Auto auto2 = new Auto();
		auto2.setAutonum("bj1231");
		auto2.setAutotype("bus");
		
		garage.addGarageAuto(auto1);
		garage.addGarageAuto(auto2);
		
		em.persist(garage);
		em.getTransaction().commit();
		em.close();
		factory.close();
	}

 运行以上save()方法之后，数据库中只对应的表，但是只有garage表中被存入了数据，而auto表中没有被存入数据，仅仅是生成了表而已。

观察发出的sql语句:

 

-----------------------------------------------------------------------

当把

@OneToMany(mappedBy="garage")
    public Set<Auto> getAutos() {
        return autos;
    } 

改为：

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

即多添加了一行cascade={CascadeType.PERSIST} 申明级联级联保存

删除前面生成的数据库表garage 和 auto

再次运行save()方法

这是我们看到数据库中都有对应的记录

 

观察发出的sql语句:

Hibernate: insert into Garage (garagenum) values (?)
Hibernate: insert into Auto (autonum, autotype, garageid) values (?, ?, ?)
Hibernate: insert into Auto (autonum, autotype, garageid) values (?, ?, ?)