jpa级联操作详解1-级联保存(CascadeType.PERSIST)

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jpa级联操作详解1(cascade) 之 cascade={CascadeType.PERSIST}

onetomany 一对多关联 实体bean：汽车和车库

（一）

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。

数据库中的表数据：

+-----+-----------+
| gid | garagenum |
+-----+-----------+
| 1 | room1 |
+-----+-----------+

 

mysql> select * from auto;
Empty set (0.00 sec)

这儿可以注意到虽然生成了auto数据库表，但是无法存储有关auto的数据，因为没有先保存auto或设置级联保存

观察发出的sql语句:

Hibernate: insert into Garage (garagenum) values (?)

 

 

（二）先保存auto

将junit测试类中的save方法改为

@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(auto1);
em.persist(auto2);
em.persist(garage);
em.getTransaction().commit();
em.close();
factory.close();
}

观察发出的sql语句：

Hibernate: insert into Auto (autonum, autotype, garageid) values (?, ?, ?)
Hibernate: insert into Auto (autonum, autotype, garageid) values (?, ?, ?)
Hibernate: insert into Garage (garagenum) values (?)
Hibernate: update Auto set autonum=?, autotype=?, garageid=? where autoId=?
Hibernate: update Auto set autonum=?, autotype=?, garageid=? where autoId=?

当然也生成了对应的数据记录，但是对数据库进行了5次操作

 

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

 

mysql> select * from auto;
+--------+---------+----------+----------+
| autoId | autonum | autotype | garageid |
+--------+---------+----------+----------+
| 1 | bj0000 | car | 1 |
| 2 | bj1231 | bus | 1 |
+--------+---------+----------+----------+

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

（三）设置cascade={CascadeType.PERSIST}

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

+-----+-----------+
| gid | garagenum |
+-----+-----------+
| 1 | room1 |
+-----+-----------+

 

+--------+---------+----------+----------+
| autoId | autonum | autotype | garageid |
+--------+---------+----------+----------+
| 1 | bj0000 | car | 1 |
| 2 | bj1231 | bus | 1 |
+--------+---------+----------+----------+

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 (?, ?, ?)