hibernate Annotation 双向one2many
主控方：House.java
package com.yazuo.entity.annotation.one2many;
import java.io.Serializable;
import javax.persistence.CascadeType;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import javax.persistence.SequenceGenerator;
import javax.persistence.Table;
@Entity
@Table(name="house")
@SequenceGenerator(name="house_id_seq",sequenceName="house_id_seq",allocationSize=1)
public class House implements Serializable{
/**
*
*/
private static final long serialVersionUID = 4889427366089042926L;
@Id
@GeneratedValue(generator="house_id_seq",strategy=GenerationType.SEQUENCE)
private Integer id;
private String address;
@ManyToOne(cascade=CascadeType.ALL,fetch=FetchType.LAZY)
@JoinColumn(name="person_id")
private Person person;
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getAddress() {
return address;
}
public void setAddress(String address) {
this.address = address;
}
public Person getPerson() {
return person;
}
public void setPerson(Person person) {
this.person = person;
}
}
被控方：Person.java
package com.yazuo.entity.annotation.one2many;
import java.io.Serializable;
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.GenerationType;
import javax.persistence.Id;
import javax.persistence.OneToMany;
import javax.persistence.SequenceGenerator;
import javax.persistence.Table;
@Entity
@Table(name="person")
@SequenceGenerator(name="person_id_seq",sequenceName="person_id_seq",allocationSize=1)
public class Person implements Serializable{
/**
*
*/
private static final long serialVersionUID = 4865848211361074151L;
@Id
@GeneratedValue(generator="person_id_seq",strategy=GenerationType.SEQUENCE)
private Integer id;
private String name;
@OneToMany(mappedBy="person")
private Set<House> houses = new HashSet<House>();
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Set<House> getHouses() {
return houses;
}
public void setHouses(Set<House> houses) {
this.houses = houses;
}
}
Test.java
package com.yazuo.entity.annotation.one2many;
import java.util.HashSet;
import java.util.Set;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.AnnotationConfiguration;
public class Test {
@org.junit.Test
public void add() throws Exception {
AnnotationConfiguration cfg = new AnnotationConfiguration();
SessionFactory sf = cfg.configure().buildSessionFactory();
Session session = sf.openSession();
Person person = new Person();
person.setName("person");
House house1 = new House();
House house2 = new House();
house1.setAddress("address1");
house2.setAddress("address2");
house1.setPerson(person);
house2.setPerson(person);
Set<House> houses = new HashSet<House>();
houses.add(house1);
houses.add(house2);
session.save(house1);
person.setHouses(houses);
session.flush();
session.close();
sf.close();
}
@org.junit.Test
public void findPersonById() throws Exception {
AnnotationConfiguration cfg = new AnnotationConfiguration();
SessionFactory sf = cfg.configure().buildSessionFactory();
Session session = sf.openSession();
String hql = "from Person p where p.id = 3";
Person person = (Person) session.createQuery(hql).list().get(0);
System.out.println(person.getName());
System.out.println(person.getHouses().size());
session.flush();
session.close();
sf.close();
}
@org.junit.Test
public void findHouseById() throws Exception {
AnnotationConfiguration cfg = new AnnotationConfiguration();
SessionFactory sf = cfg.configure().buildSessionFactory();
Session session = sf.openSession();
String hql = "from House h where h.id = 1";
House house = (House) session.createQuery(hql).list().get(0);
System.out.println(house.getAddress());
// System.out.println(house.getPerson().getName());
session.flush();
session.close();
sf.close();
}
@org.junit.Test
public void deleteHouseById() throws Exception {
AnnotationConfiguration cfg = new AnnotationConfiguration();
SessionFactory sf = cfg.configure().buildSessionFactory();
Session session = sf.openSession();
String hql = "from House h where h.id = 1";
House house = (House) session.createQuery(hql).list().get(0);
session.delete(house);
session.flush();
session.close();
sf.close();
}
@org.junit.Test
public void deletePersonById() throws Exception {
AnnotationConfiguration cfg = new AnnotationConfiguration();
SessionFactory sf = cfg.configure().buildSessionFactory();
Session session = sf.openSession();
String hql = "from Person p where p.id = 3";
Person person = (Person) session.createQuery(hql).list().get(0);
session.delete(person);
session.flush();
session.close();
sf.close();
}
}
小结：
终于看到 fetch=FetchType.LAZY 的效果了
在 one-to-many 双向关联中
双方都不加 fetch=FetchType.LAZY
执行 findPersonById() 时，不会查找 person.house，只有在显示的调用 person.getHouse()
才会打印出 select sql。
执行 findHouseById() 时，会自动查找 house.person
当将house 的 many-to-one(fetch=FetchType.LAZY)，则不会自动查找 house.person，只有在显示的调用 house.getPerson() 才会打印出 select sql