hibernate延遲載入以及no-session
延遲載入:延遲載入(lazy load懶載入)是當在真正需要資料時,才執行SQL語句進行查詢,避免了無謂的效能開銷。
延遲載入分類:
01.類級別的查詢策略
02.一對多和多對多關聯的查詢策略
03.多對一關聯的查詢策略
類級別的查詢策略
1.類級別可選的檢索策略包括立即檢索和延遲檢索,預設為延遲檢索
1.1立即檢索:立即載入檢索方法指定的物件,立即傳送SQL
1.2 延遲檢索:延遲載入檢索方法制定的物件.在使用具體的屬性時,再進行載入,才傳送SQL
2.無論<class>元素的lazy屬性是true還是false,Session的get()方法及Query
3.若<class>元素的lazy屬性為true或預設值,Session的load()方法不會執行查詢資料庫表的SELECT語句,僅返回代理類物件的例項,該代理類例項有如下特徵:
3.1 由Hibernate在執行時採用CGLIB工具動態生成3.2 Hibernate建立代理類例項時,僅初始化其OID屬性3.3在應用程式第一次訪問代理類例項的非OID屬性時,Hibernate會初始化代理類例項
3.4注意:類級別檢索策略僅適用於load()方法
(立即載入,延遲載入等)檢索,通過set元素的lazy屬性設定。
01.一對多或者多對多檢索策略由
Lazy:決定關聯物件初始化時機
Fetch:決定SQL語句構建形式
02.fetch取值
Join:迫切左外連線
Select:多條簡單SQL(預設值)
Subselect:子查詢
03.fetch和lazy組合
解析:fetch=”join” lazy會被忽略,迫切左外連線的立即檢索
Fetch=”select” lazy=”false” 多條簡單SQL立即檢索
Fetch=”select” lazy=”true” 多條語句延遲檢索
Fetch=”select” lazy=”extra” 多條語句及其懶惰檢索
Fetch=”subselect” lazy=”false” 子查詢立即檢索
Fetch=”subselect” lazy=”true” 子查詢延遲檢索
Fetch=”subselect” lazy=”extra” 子查詢及其懶惰檢索
Extra:極其懶惰,只有訪問集合物件的屬性時才會載入,訪問集合本身的屬性時(例如,集合大小,生成count),不會立即載入。
注意:query的list()會忽略對映檔案配置的左外連線查詢,此時lazy屬性重新生效。
具體案例
首先我們用的hibernate.hbm.xml都是一個的 直接上傳一個就ok. 連線資料庫 對應哪個包下仔細看一下。
<?xml version='1.0' encoding='UTF-8'?>
<!DOCTYPE hibernate-configuration PUBLIC
"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
<!-- <session-factory>
<property name="myeclipse.connection.profile">JDBC for MySQL</property>
<property name="connection.driver_class">com.mysql.jdbc.Driver</property>
<property name="connection.url">jdbc:mysql://localhost:3306/book</property>
<property name="connection.username">root</property>
<property name="connection.password"></property>
<property name="hibernate.show_sql">true</property>
<property name="dialect">org.hibernate.dialect.MySQLDialect</property>
<property name="hibernate.format_sql">true</property>
<!–生成特定資料庫sql–>
<property name="hibernate.hbm2ddl.auto">update</property>
<!–thread指定當前執行緒來跟蹤管理–>
<property name="current_session_context_class">thread</property>
<mapping resource="Dog.xml"></mapping>
</session-factory>
-->
<session-factory>
<property name="connection.driver_class">oracle.jdbc.OracleDriver</property>
<property name="connection.url">jdbc:oracle:thin:@localhost:1521:orcl</property>
<property name="connection.username">sll</property>
<property name="connection.password">sll</property>
<!-- SQL dialect -->
<property name="dialect">org.hibernate.dialect.Oracle10gDialect</property>
<property name="current_session_context_class">thread</property>
<property name="show_sql">true</property>
<property name="hbm2ddl.auto">update</property>
<property name="connection.autocommit">true</property>
<!-- <mapping resource="cn/happy/hibernate01/Cat.hbm.xml"/>
<mapping resource="cn/happy/hibernate02/Dept.hbm.xml"/>-->
<!-- <mapping resource="cn/happy/hibernate03hql/Emp.hbm.xml"/>
<mapping resource="cn/happy/hibernate04pagelist/Emp.hbm.xml"/>
<mapping resource="cn/happy/hibernate06mapping/Emp.hbm.xml"/>
<mapping resource="cn/happy/hibernate06mapping/Dept.hbm.xml"/>
<mapping resource="cn/happy/hibernate07onttomany/Emp.hbm.xml"/>
<mapping resource="cn/happy/hibernate07onttomany/Dept.hbm.xml"/>
-->
<!-- <mapping resource="cn/happy/hibernate08save/Emp.hbm.xml"/>
<mapping resource="cn/happy/hibernate08save/Dept.hbm.xml"/>
<mapping resource="cn/happy/hibernate09manytomany/Employee.hbm.xml"/>
<mapping resource="cn/happy/hibernate09manytomany/Project.hbm.xml"/>
<mapping resource="cn/happy/hibernate11lazyLoad/Student.hbm.xml"/>-->
<!-- <mapping resource="cn/happy/hibernate11lazyLoad/Emp.hbm.xml"/>
<mapping resource="cn/happy/hibernate11lazyLoad/Dept.hbm.xml"/>-->
<!--no-session-->
<!-- <mapping resource="cn/happy/hibernate12nosession/Emp.hbm.xml"/>
<mapping resource="cn/happy/hibernate12nosession/Dept.hbm.xml"/>
-->
<mapping resource="cn/happy/hibernate10opensessioninview/Student.hbm.xml"/>
<mapping class="cn.happy.hibernate13zj.Dept"></mapping>
<mapping class="cn.happy.hibernate14onetoone.Humen"></mapping>
<mapping class="cn.happy.hibernate14onetoone.Card"></mapping>
</session-factory>
</hibernate-configuration>
然後因為這個沒有用到註解 所以我們需要小配置
首先我們看一下實體類。
package cn.happy.hibernate11lazyLoad;
import java.util.Date;
/**
* Created by linlin on 2017/10/9.
*/
public class Student {
private Integer stuno;
private String stuname;
private Integer stuage;
private Date studate;
public Integer getStuno() {
return stuno;
}
public void setStuno(Integer stuno) {
this.stuno = stuno;
}
public String getStuname() {
return stuname;
}
public void setStuname(String stuname) {
this.stuname = stuname;
}
public Integer getStuage() {
return stuage;
}
public void setStuage(Integer stuage) {
this.stuage = stuage;
}
public Date getStudate() {
return studate;
}
public void setStudate(Date studate) {
this.studate = studate;
}
}
每個 案例也就那幾步
小配置 :
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="cn.happy.hibernate11lazyLoad">
<class name="Student" table="StudentNew" schema="sll" lazy="true">
<id name="stuno" column="stuno">
<generator class="native"></generator>
</id>
<property name="stuname" />
<property name="stuage"/>
<property name="studate"/>
</class>
</hibernate-mapping>
測試類:
package cn.happy.test;
import cn.happy.hibernate11lazyLoad.Dept;
import cn.happy.hibernate11lazyLoad.Emp;
import cn.happy.hibernate11lazyLoad.Student;
import cn.happy.hibernate12nosession.biz.HibernateBiz;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;
import org.junit.Before;
import org.junit.Test;
import java.util.List;
import java.util.Set;
/**
* Created by linlin on 2017/9/22.
*/
public class test1009 {
Configuration cfg;
Transaction tx;
Session session;
SessionFactory factory;
@Before
public void myBefore() {
//建立配置物件
cfg = new Configuration().configure("Hibernate.cfg.xml");
//根據配置物件建立SessionFactory
factory = cfg.buildSessionFactory();
//根據SessionFactory建立Session
session = factory.openSession();
//在Session建立後開啟事務
tx = session.beginTransaction();
}
@Test
public void testmanyToOne() {
Dept dept = session.get(Dept.class, 14);
Set<Emp> emps = dept.getEmps();
emps.size();
}
@Test
public void testmanyToOne0() {
Student student = session.load(Student.class, 1);
}
}
這裡下面的方法是上面測試
下面這個是實體類和小配置是上面的方法
package cn.happy.hibernate11lazyLoad;
import java.util.HashSet;
import java.util.Set;
/**
* Created by linlin on 2017/9/24.
*/
public class Dept {
private Integer deptno;
private String deptname;
private Set<Emp> emps=new HashSet<Emp>();
public Set<Emp> getEmps() {
return emps;
}
public void setEmps(Set<Emp> emps) {
this.emps = emps;
}
public Dept() {
}
public Integer getDeptno() {
return deptno;
}
public void setDeptno(Integer deptno) {
this.deptno = deptno;
}
public String getDeptname() {
return deptname;
}
public void setDeptname(String deptname) {
this.deptname = deptname;
}
}
package cn.happy.hibernate11lazyLoad;
/**
* Created by linlin on 2017/9/24.
*/
public class Emp {
private Integer empno;
private String ename;
private Dept dept;
public Dept getDept() {
return dept;
}
public void setDept(Dept dept) {
this.dept = dept;
}
public Integer getEmpno() {
return empno;
}
public void setEmpno(Integer empno) {
this.empno = empno;
}
public String getEname() {
return ename;
}
public void setEname(String ename) {
this.ename = ename;
}
}
小配置:
<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="cn.happy.hibernate08save">
<class name="cn.happy.hibernate11lazyLoad.Dept" table="Dept" schema="sll">
<id name="deptno" column="deptno">
<generator class="native"/>
</id>
<property name="deptname" column="deptname"/>
<set name="emps" lazy="false" fetch="join">
<key column="deptno"/>
<one-to-many class="Emp"/>
</set>
</class>
</hibernate-mapping>
<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="cn.happy.hibernate08save">
<class name="cn.happy.hibernate11lazyLoad.Emp" table="Emp" schema="sll">
<id name="empno" column="empno">
<generator class="native"/>
</id>
<property name="ename" column="enmae"/>
<many-to-one name="dept" column="deptno" class="Dept"></many-to-one>
</class>
</hibernate-mapping>
上面是延遲載入的 案例
下面是no-session
biz:
package cn.happy.hibernate12nosession.biz;
import cn.happy.hibernate12nosession.Emp;
import cn.happy.hibernate12nosession.dao.HibernateDAO;
import cn.happy.hibernate12nosession.util.HibernateUtil;
import org.hibernate.Hibernate;
import org.hibernate.Transaction;
import java.io.Serializable;
/**
* Created by linlin on 2017/10/9.
*/
public class HibernateBiz {
HibernateDAO dao=new HibernateDAO();
public Object get(Class clazz, Serializable id) {
Transaction tx = HibernateUtil.currentSession().beginTransaction();
Object obj= dao.get(clazz, id);
/* Emp emp=(Emp)obj;
emp.getEname();*/
if(!Hibernate.isInitialized(obj)){
Hibernate.initialize(obj);
}
System.out.println("==============================================");
tx.commit();
HibernateUtil.closeSession();
return obj;
}
}
dao:
package cn.happy.hibernate12nosession.dao;
import cn.happy.hibernate10opensessioninview.util.HibernateUtil;
import java.io.Serializable;
/**
* Created by linlin on 2017/10/9.
*/
public class HibernateDAO {
public Object get(Class clazz, Serializable id) {
Object result= HibernateUtil.getSession().load(clazz,id);
return result;
}
}
util:
package cn.happy.hibernate12nosession.util;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
/**
* Created by linlin on 2017/10/6.
*/
public class HibernateUtil {
//getCurrentSession()底層實現原理
//ThreadLocal變數
public static final ThreadLocal<Session> threadTL=new ThreadLocal<Session>();
//我想直接呼叫一個方法,獲取Session
//定義一個sessionFactory物件
private static SessionFactory factory;
private static Configuration cfg;
static{
cfg=new Configuration().configure();
factory=cfg.buildSessionFactory();
}
//提供一個靜態方法
public static Session currentSession(){
Session session=threadTL.get();
if(session==null){ //當前執行緒中沒有session物件
session=factory.openSession();
threadTL.set(session);
}
return session;
}
//關閉session
public static void closeSession(){
//獲取執行緒中的session
Session session = threadTL.get();
if (session!=null) {
threadTL.set(null);
session.close();
}
}
}
Dept Emp和上面的一樣的
測試類
package cn.happy.test;
import cn.happy.hibernate12nosession.Emp;
import cn.happy.hibernate12nosession.biz.HibernateBiz;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;
import org.junit.Before;
import org.junit.Test;
import java.util.Set;
/**
* Created by linlin on 2017/9/22.
*/
public class test1009_01 {
Configuration cfg;
Transaction tx;
Session session;
SessionFactory factory;
@Before
public void myBefore() {
//建立配置物件
cfg = new Configuration().configure("Hibernate.cfg.xml");
//根據配置物件建立SessionFactory
factory = cfg.buildSessionFactory();
//根據SessionFactory建立Session
session = factory.openSession();
//在Session建立後開啟事務
tx = session.beginTransaction();
}
//no-session
@Test
public void loadGetTest() {
HibernateBiz biz = new HibernateBiz();
Emp emp = (Emp) biz.get(Emp.class, 1);
System.out.println(emp.getEname());
}
}