package com.tao.service;
import java.util.Iterator;
import java.util.List;
import java.util.Set;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;
import com.tao.entity.*;
import com.tao.entity.Class;
import com.tao.util.HibernateUtil;
public class TestLay {
SessionFactory sessionFactory = HibernateUtil.getSessionFactory();
private Session session;
@Before
public void setUp() throws Exception {
session = sessionFactory.openSession();
session.beginTransaction();
}
@After
public void tearDown() throws Exception {
session.getTransaction().commit();
session.close();
}
@Test
public void testOne2MantSave() throws Exception {
Class class1 = new Class();
class1.setClaaName("精英班");
Student student1 = new Student();
student1.setStudentName("孔明");
student1.setC(class1);
Student student2 = new Student();
student2.setStudentName("子房");
student2.setC(class1);
session.save(student1);
session.save(student2);
}
@Test
public void testQueryOne2Many() throws Exception {
List<Class> list = session.createQuery("from Class").list();
Iterator<Class> iterator = list.iterator();
while(iterator.hasNext()){
Class next = iterator.next();
Set<Student> students = next.getStudents();
for(Student s:students){
System.out.println(next.getClaaName()+"學生:"+s.getStudentName());
}
}
}
}
console:
Hibernate: select class0_.class_id as class_id1_0_, class0_.class_name as class_na2_0_ from Class class0_
Hibernate: select students0_.c_id as c_id3_0_0_, students0_.student_id as student_1_1_0_, students0_.student_id as student_1_1_1_, students0_.student_name as student_2_1_1_, students0_.c_id as c_id3_1_1_ from Student students0_ where students0_.c_id=?
精英班學生:子房
精英班學生:孔明
Hibernate: select students0_.c_id as c_id3_0_0_, students0_.student_id as student_1_1_0_, students0_.student_id as student_1_1_1_, students0_.student_name as student_2_1_1_, students0_.c_id as c_id3_1_1_ from Student students0_ where students0_.c_id=?
培優班學生:李斯
培優班學生:管仲
Hibernate: select students0_.c_id as c_id3_0_0_, students0_.student_id as student_1_1_0_, students0_.student_id as student_1_1_1_, students0_.student_name as student_2_1_1_, students0_.c_id as c_id3_1_1_ from Student students0_ where students0_.c_id=?
基本的準備工作都搭建好了，現在我們來測試一下懶加載。
延遲檢索 用到的時候再去查 lazy="true" set端 一對多
級聯資料不會先擷取
先在Class.hbm.xml裡加上 lazy="true",
九、Hibernate檢索政策 —— Lazy、batch-size、Fetch
然後進行測試：
@Test
public void testLazyTrue() throws Exception {
Class class1 = (Class) session.get(Class.class, 1);
Set<Student> studentsList = class1.getStudents();
// studentsList.iterator();
}
@Test
public void testFetch1() throws Exception {
List<Class> classList = session.createQuery("from Class").list();
Iterator<Class> it = classList.iterator();
Class c1 = it.next();
Class c2 = it.next();
Class c3 = it.next();
c1.getStudents().iterator();
c2.getStudents().iterator();
c3.getStudents().iterator();
}
看console 和批量立即檢索沒什麼差別：
INFO: HHH000126: Indexes: [fk_swj9e42aicxndumd3odiux122, primary]
一月 31, 2019 1:47:24 下午 org.hibernate.tool.hbm2ddl.SchemaUpdate execute
INFO: HHH000232: Schema update complete
Hibernate: select class0_.class_id as class_id1_0_, class0_.class_name as class_na2_0_ from Class class0_
Hibernate: select students0_.c_id as c_id3_0_1_, students0_.student_id as student_1_1_1_, students0_.student_id as student_1_1_0_, students0_.student_name as student_2_1_0_, students0_.c_id as c_id3_1_0_ from Student students0_ where students0_.c_id in (?, ?, ?)
我們把這邊的 fetch = "subselect" 設定一下,
九、Hibernate檢索政策 —— Lazy、batch-size、Fetch
然後繼續執行上述方法，再看控制台列印的SQL:
INFO: HHH000232: Schema update complete
Hibernate: select class0_.class_id as class_id1_0_, class0_.class_name as class_na2_0_ from Class class0_
Hibernate: select students0_.c_id as c_id3_0_1_, students0_.student_id as student_1_1_1_, students0_.student_id as student_1_1_0_, students0_.student_name as student_2_1_0_, students0_.c_id as c_id3_1_0_ from Student students0_ where students0_.c_id in (select class0_.class_id from Class class0_)
九、Hibernate檢索政策 —— Lazy、batch-size、Fetch
發現用了子查詢，在某些情況下使用子查詢，效率是會提高的
"fetch" = "join" 使用外連接配接查詢
我們先把fetch 改回預設的 fetch= "select" ,然後執行一下測試方法：
@Test
public void testFetch2() throws Exception {
Class class1 = (Class) session.get(Class.class, 1);
}
看console:
九、Hibernate檢索政策 —— Lazy、batch-size、Fetch
get 是直接去資料庫查 且會把關聯對象資料也查出來 是以此處如果預設的fetch = "select" 就應該是兩條資料.
