Hibernate应用cascade&fetch
简单说明：cascade和fetch是Hibernate读取和写入数据库对象两个参数，cascade（层叠）管写入（Save、Update...）；fetch管读取（Load、Get...）
一、cascade——它是用来指明做什么操作的时候关联对象绑定在一起：
a)CascadeType.ALL 表示所有情况
b)CascadeType.MERGE表示在Save或UPdate的情况
c)CascadeType.REFRESH=A 里面需要读B改过之后的数据
d)CascadeType.PERSIST
e)CascadeType.REMOVE
总之，用得比较多的是CascadeType.All
二、fetch——它是用来指明读取数据时关联对象的情况：
a)a)FetchType.EAGER
b)FetchType.LAZY(默认)
三、实例代码：
团队类：
package com.sean.model.one2many;
import java.util.HashSet;
import java.util.Set;
import javax.persistence.CascadeType;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.OneToMany;
import javax.persistence.Table;
/**
* 一对多：团队对象
*
* @author Sean 2013-2-26
*
*/
@Entity
@Table(name = "p_group")
public class Group {
private int id;
private String name;
private Set pset = new HashSet();
@OneToMany(cascade = (CascadeType.ALL), fetch = FetchType.EAGER)
public Set getPset() {
return pset;
}
public void setPset(Set pset) {
this.pset = pset;
}
@Id
@GeneratedValue
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}
成员类：
package com.sean.model.one2many;
import javax.persistence.CascadeType;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.ManyToOne;
/**
* 一对多：成员对象
*
* @author Sean 2013-2-26
*
*/
@Entity
public class Person {
private int id;
private String name;
private Group group;
@ManyToOne(cascade = CascadeType.ALL)
public Group getGroup() {
return group;
}
public void setGroup(Group group) {
this.group = group;
}
@Id
@GeneratedValue
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}
测试方法：
public void testGroup2Person() {
Group g = new Group();
g.setName("淘宝");
Person p1 = new Person();
Person p2 = new Person();
Person p3 = new Person();
Person p4 = new Person();
p1.setName("赵一");
// p1.setGroup(g);
p2.setName("赵二");
// p2.setGroup(g);
p3.setName("赵三");
// p3.setGroup(g);
p4.setName("赵四");
// p4.setGroup(g);
g.getPset().add(p1);
g.getPset().add(p2);
g.getPset().add(p3);
g.getPset().add(p4);
SessionFactory factory = new AnnotationConfiguration().configure()
.buildSessionFactory();
Session session = factory.openSession();
session.beginTransaction();
session.save(g);
session.getTransaction().commit();
session.close();
factory.close();
}
public void testLoadGroup() {
testGroup2Person();
SessionFactory factory = new AnnotationConfiguration().configure()
.buildSessionFactory();
Session session = factory.openSession();
session.beginTransaction();
Group group = (Group) session.get(Group.class, 17);
session.getTransaction().commit();
session.close();
factory.close();
for (Person i : group.getPset()) {
System.out.println(i.getName());
}
}