（九）Hibernate 检索策略

所有项目导入对应的hibernate的jar包、mysql的jar包和添加每次都需要用到的HibernateUtil.java

这里的hibernate.cfg.xml配置信息我就不再写了

第一节：检索策略属性Lazy

Lazy:true (默认) 延迟检索；set 端一对多

Lazy:false 立即检索；set 端一对多

Lazy:extra 增强延迟检索； set 端一对多

Lazy:proxy(默认) 延迟检索；many-to-one 多对一

Lazy:no-proxy 无代理延迟检索；many-to-one 多对一(需要编译时字节码增强)

Lazy:true (默认) 延迟检索；set 端一对多

Class.java

 package com.wishwzp.model;

 import java.util.HashSet;
 import java.util.Set;

 public class Class {

     private long id;
     private String name;
     private Set<Student> students=new HashSet<Student>();

     public long getId() {
         return id;
     }
     public void setId(long id) {
         this.id = id;
     }
     public String getName() {
         return name;
     }
     public void setName(String name) {
         this.name = name;
     }
     public Set<Student> getStudents() {
         return students;
     }
     public void setStudents(Set<Student> students) {
         this.students = students;
     }

 }

Student.java

 package com.wishwzp.model;

 public class Student {

     private long id;
     private String name;
     private Class c;

     public long getId() {
         return id;
     }
     public void setId(long id) {
         this.id = id;
     }
     public String getName() {
         return name;
     }
     public void setName(String name) {
         this.name = name;
     }

     public Class getC() {
         return c;
     }
     public void setC(Class c) {
         this.c = c;
     }
     @Override
     public String toString() {
         return "Student [id=" + id + ", name=" + name + "]";
     }
 }

Class.hbm.xml

 <?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="com.wishwzp.model">

     <class name="Class" table="t_class">
         <id name="id" column="classId">
             <generator class="native"></generator>
         </id>

         <property name="name" column="className"></property>

         <set name="students" cascade="delete" inverse="true" lazy="true">
             <key column="classId"></key>
             <one-to-many class="com.wishwzp.model.Student"/>
         </set>
     </class>

 </hibernate-mapping>

Student.hbm.xml

 <?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="com.wishwzp.model">

     <class name="Student" table="t_student">
         <id name="id" column="stuId">
             <generator class="native"></generator>
         </id>

         <property name="name" column="stuName"></property>

         <many-to-one name="c" column="classId" class="com.wishwzp.model.Class" cascade="save-update"></many-to-one>
     </class>

 </hibernate-mapping>

StudentTest.java

 package com.wishwzp.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.wishwzp.model.Class;
 import com.wishwzp.model.Student;
 import com.wishwzp.util.HibernateUtil;

 public class StudentTest {

     private SessionFactory sessionFactory=HibernateUtil.getSessionFactory();
     private Session session;

     @Before
     public void setUp() throws Exception {
         session=sessionFactory.openSession(); // 生成一个session
         session.beginTransaction(); // 开启事务
     }

     @After
     public void tearDown() throws Exception {
          session.getTransaction().commit(); // 提交事务
          session.close(); // 关闭session
     }

     @Test
     public void testLazy1() {
         Class c=(Class)session.get(Class.class, Long.valueOf(1));
         Set<Student> studentList=(Set<Student>)c.getStudents();
         studentList.iterator();
     }
 }

数据库里面的信息数据：

运行显示结果：

Hibernate: select class0_.classId as classId1_0_0_, class0_.className as classNam2_0_0_ from t_class class0_ where class0_.classId=?
Hibernate: select students0_.classId as classId3_0_0_, students0_.stuId as stuId1_1_0_, students0_.stuId as stuId1_1_1_, students0_.stuName as stuName2_1_1_, students0_.classId as classId3_1_1_ from t_student students0_ where students0_.classId=?

Lazy:false 立即检索；set 端一对多

Class.hbm.xml

 <?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="com.wishwzp.model">

     <class name="Class" table="t_class">
         <id name="id" column="classId">
             <generator class="native"></generator>
         </id>

         <property name="name" column="className"></property>

         <set name="students" cascade="delete" inverse="true" lazy="false">
             <key column="classId"></key>
             <one-to-many class="com.wishwzp.model.Student"/>
         </set>
     </class>

 </hibernate-mapping>

StudentTest.java

 package com.wishwzp.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.wishwzp.model.Class;
 import com.wishwzp.model.Student;
 import com.wishwzp.util.HibernateUtil;

 public class StudentTest {

     private SessionFactory sessionFactory=HibernateUtil.getSessionFactory();
     private Session session;

     @Before
     public void setUp() throws Exception {
         session=sessionFactory.openSession(); // 生成一个session
         session.beginTransaction(); // 开启事务
     }

     @After
     public void tearDown() throws Exception {
          session.getTransaction().commit(); // 提交事务
          session.close(); // 关闭session
     }

     @Test
     public void testLazy1() {
         Class c=(Class)session.get(Class.class, Long.valueOf(1));

     }

 }

还是上面第一个的数据库信息。

运行显示结果：

Hibernate: select class0_.classId as classId1_0_0_, class0_.className as classNam2_0_0_ from t_class class0_ where class0_.classId=?
Hibernate: select students0_.classId as classId3_0_0_, students0_.stuId as stuId1_1_0_, students0_.stuId as stuId1_1_1_, students0_.stuName as stuName2_1_1_, students0_.classId as classId3_1_1_ from t_student students0_ where students0_.classId=?

Lazy:extra 增强延迟检索； set 端一对多

Class.hbm.xml

 <?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="com.wishwzp.model">

     <class name="Class" table="t_class">
         <id name="id" column="classId">
             <generator class="native"></generator>
         </id>

         <property name="name" column="className"></property>

         <set name="students" cascade="delete" inverse="true" lazy="extra">
             <key column="classId"></key>
             <one-to-many class="com.wishwzp.model.Student"/>
         </set>
     </class>

 </hibernate-mapping>

StudentTest.java

 package com.wishwzp.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.wishwzp.model.Class;
 import com.wishwzp.model.Student;
 import com.wishwzp.util.HibernateUtil;

 public class StudentTest {

     private SessionFactory sessionFactory=HibernateUtil.getSessionFactory();
     private Session session;

     @Before
     public void setUp() throws Exception {
         session=sessionFactory.openSession(); // 生成一个session
         session.beginTransaction(); // 开启事务
     }

     @After
     public void tearDown() throws Exception {
          session.getTransaction().commit(); // 提交事务
          session.close(); // 关闭session
     }

     @Test
     public void testLazy1() {
         Class c=(Class)session.get(Class.class, Long.valueOf(1));
         Set<Student> studentList=(Set<Student>)c.getStudents();
         System.out.println(studentList.size());
     }

 }

还是上面第一个的数据库信息。

运行结果显示：

Hibernate: select class0_.classId as classId1_0_0_, class0_.className as classNam2_0_0_ from t_class class0_ where class0_.classId=?
Hibernate: select count(stuId) from t_student where classId =?
3

Lazy:proxy(默认) 延迟检索；many-to-one 多对一

Student.hbm.xml

 <?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="com.wishwzp.model">

     <class name="Student" table="t_student">
         <id name="id" column="stuId">
             <generator class="native"></generator>
         </id>

         <property name="name" column="stuName"></property>

         <many-to-one name="c" column="classId" class="com.wishwzp.model.Class" cascade="save-update" lazy="proxy"></many-to-one>
     </class>

 </hibernate-mapping>

StudentTest.java

 package com.wishwzp.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.wishwzp.model.Class;
 import com.wishwzp.model.Student;
 import com.wishwzp.util.HibernateUtil;

 public class StudentTest {

     private SessionFactory sessionFactory=HibernateUtil.getSessionFactory();
     private Session session;

     @Before
     public void setUp() throws Exception {
         session=sessionFactory.openSession(); // 生成一个session
         session.beginTransaction(); // 开启事务
     }

     @After
     public void tearDown() throws Exception {
          session.getTransaction().commit(); // 提交事务
          session.close(); // 关闭session
     }

     @Test
     public void testLazy2() {
         Student student=(Student)session.get(Student.class, Long.valueOf(1));
         student.getC().getName();
     }

 }

运行显示结果：

Hibernate: select student0_.stuId as stuId1_1_0_, student0_.stuName as stuName2_1_0_, student0_.classId as classId3_1_0_ from t_student student0_ where student0_.stuId=?
Hibernate: select class0_.classId as classId1_0_0_, class0_.className as classNam2_0_0_ from t_class class0_ where class0_.classId=?

Lazy:no-proxy 无代理延迟检索；many-to-one 多对一(需要编译时字节码增强)

Student.hbm.xml

 <?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="com.wishwzp.model">

     <class name="Student" table="t_student">
         <id name="id" column="stuId">
             <generator class="native"></generator>
         </id>

         <property name="name" column="stuName"></property>

         <many-to-one name="c" column="classId" class="com.wishwzp.model.Class" cascade="save-update" lazy="no-proxy"></many-to-one>
     </class>

 </hibernate-mapping>

StudentTest.java和上面一样

第二节：检索策略属性batch-size

1，批量延迟检索；

2，批量立即检索；

1，批量延迟检索；

Class.hbm.xml

 <?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="com.wishwzp.model">

     <class name="Class" table="t_class">
         <id name="id" column="classId">
             <generator class="native"></generator>
         </id>

         <property name="name" column="className"></property>

         <set name="students" cascade="delete" inverse="true" lazy="true" batch-size="3">
             <key column="classId"></key>
             <one-to-many class="com.wishwzp.model.Student"/>
         </set>
     </class>

 </hibernate-mapping>

StudentTest.java

 package com.wishwzp.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.wishwzp.model.Class;
 import com.wishwzp.model.Student;
 import com.wishwzp.util.HibernateUtil;

 public class StudentTest {

     private SessionFactory sessionFactory=HibernateUtil.getSessionFactory();
     private Session session;

     @Before
     public void setUp() throws Exception {
         session=sessionFactory.openSession(); // 生成一个session
         session.beginTransaction(); // 开启事务
     }

     @After
     public void tearDown() throws Exception {
          session.getTransaction().commit(); // 提交事务
          session.close(); // 关闭session
     }

     @Test
     public void testBatch1(){
         List<Class> classList=session.createQuery("from Class").list();
         Iterator it=classList.iterator();
         Class c1=(Class)it.next();
         Class c2=(Class)it.next();
         Class c3=(Class)it.next();
         c1.getStudents().iterator();
         c2.getStudents().iterator();
         c3.getStudents().iterator();
     }

 }

数据库多加了一条信息：

运行结果显示：

Hibernate: select class0_.classId as classId1_0_, class0_.className as classNam2_0_ from t_class class0_
Hibernate: select students0_.classId as classId3_0_1_, students0_.stuId as stuId1_1_1_, students0_.stuId as stuId1_1_0_, students0_.stuName as stuName2_1_0_, students0_.classId as classId3_1_0_ from t_student students0_ where students0_.classId in (?, ?, ?)

2，批量立即检索；

Class.hbm.xml

 <?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="com.wishwzp.model">

     <class name="Class" table="t_class">
         <id name="id" column="classId">
             <generator class="native"></generator>
         </id>

         <property name="name" column="className"></property>

         <set name="students" cascade="delete" inverse="true" lazy="false" batch-size="3">
             <key column="classId"></key>
             <one-to-many class="com.wishwzp.model.Student"/>
         </set>
     </class>

 </hibernate-mapping>

StudentTest.java

 package com.wishwzp.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.wishwzp.model.Class;
 import com.wishwzp.model.Student;
 import com.wishwzp.util.HibernateUtil;

 public class StudentTest {

     private SessionFactory sessionFactory=HibernateUtil.getSessionFactory();
     private Session session;

     @Before
     public void setUp() throws Exception {
         session=sessionFactory.openSession(); // 生成一个session
         session.beginTransaction(); // 开启事务
     }

     @After
     public void tearDown() throws Exception {
          session.getTransaction().commit(); // 提交事务
          session.close(); // 关闭session
     }

     @Test
     public void testBatch2(){
         List<Class> classList=session.createQuery("from Class").list();

     }

 }

运行结果显示：

Hibernate: select class0_.classId as classId1_0_, class0_.className as classNam2_0_ from t_class class0_
Hibernate: select students0_.classId as classId3_0_1_, students0_.stuId as stuId1_1_1_, students0_.stuId as stuId1_1_0_, students0_.stuName as stuName2_1_0_, students0_.classId as classId3_1_0_ from t_student students0_ where students0_.classId in (?, ?, ?)

假如我们将Class.hbm.xml的batch-size="3"改成batch-size="2"的话，运行结果显示：

Hibernate: select class0_.classId as classId1_0_, class0_.className as classNam2_0_ from t_class class0_
Hibernate: select students0_.classId as classId3_0_1_, students0_.stuId as stuId1_1_1_, students0_.stuId as stuId1_1_0_, students0_.stuName as stuName2_1_0_, students0_.classId as classId3_1_0_ from t_student students0_ where students0_.classId in (?, ?)
Hibernate: select students0_.classId as classId3_0_1_, students0_.stuId as stuId1_1_1_, students0_.stuId as stuId1_1_0_, students0_.stuName as stuName2_1_0_, students0_.classId as classId3_1_0_ from t_student students0_ where students0_.classId=?

第三节：检索策略属性Fetch

1，Fetch:select(默认) 查询方式；

2，Fetch:subselect 子查询方式；

3，Fetch:join 迫切左外连接查询方式；

1，Fetch:select(默认) 查询方式；

Class.hbm.xml

 <?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="com.wishwzp.model">

     <class name="Class" table="t_class">
         <id name="id" column="classId">
             <generator class="native"></generator>
         </id>

         <property name="name" column="className"></property>

         <set name="students" cascade="delete" inverse="true" lazy="false" batch-size="2" fetch="select">
             <key column="classId"></key>
             <one-to-many class="com.wishwzp.model.Student"/>
         </set>
     </class>

 </hibernate-mapping>

StudentTest.java

 package com.wishwzp.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.wishwzp.model.Class;
 import com.wishwzp.model.Student;
 import com.wishwzp.util.HibernateUtil;

 public class StudentTest {

     private SessionFactory sessionFactory=HibernateUtil.getSessionFactory();
     private Session session;

     @Before
     public void setUp() throws Exception {
         session=sessionFactory.openSession(); // 生成一个session
         session.beginTransaction(); // 开启事务
     }

     @After
     public void tearDown() throws Exception {
          session.getTransaction().commit(); // 提交事务
          session.close(); // 关闭session
     }

     @Test
     public void testFetch1(){
         List<Class> classList=session.createQuery("from Class").list();
         Iterator it=classList.iterator();
         Class c1=(Class)it.next();
         Class c2=(Class)it.next();
         Class c3=(Class)it.next();
         c1.getStudents().iterator();
         c2.getStudents().iterator();
         c3.getStudents().iterator();
     }

 }

运行结果显示：

Hibernate: select class0_.classId as classId1_0_, class0_.className as classNam2_0_ from t_class class0_
Hibernate: select students0_.classId as classId3_0_1_, students0_.stuId as stuId1_1_1_, students0_.stuId as stuId1_1_0_, students0_.stuName as stuName2_1_0_, students0_.classId as classId3_1_0_ from t_student students0_ where students0_.classId in (?, ?)
Hibernate: select students0_.classId as classId3_0_1_, students0_.stuId as stuId1_1_1_, students0_.stuId as stuId1_1_0_, students0_.stuName as stuName2_1_0_, students0_.classId as classId3_1_0_ from t_student students0_ where students0_.classId=?

2，Fetch:subselect 子查询方式；

Class.hbm.xml

 <?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="com.wishwzp.model">

     <class name="Class" table="t_class">
         <id name="id" column="classId">
             <generator class="native"></generator>
         </id>

         <property name="name" column="className"></property>

         <set name="students" cascade="delete" inverse="true" lazy="false" batch-size="2" fetch="subselect">
             <key column="classId"></key>
             <one-to-many class="com.wishwzp.model.Student"/>
         </set>
     </class>

 </hibernate-mapping>

StudentTest.java

 package com.wishwzp.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.wishwzp.model.Class;
 import com.wishwzp.model.Student;
 import com.wishwzp.util.HibernateUtil;

 public class StudentTest {

     private SessionFactory sessionFactory=HibernateUtil.getSessionFactory();
     private Session session;

     @Before
     public void setUp() throws Exception {
         session=sessionFactory.openSession(); // 生成一个session
         session.beginTransaction(); // 开启事务
     }

     @After
     public void tearDown() throws Exception {
          session.getTransaction().commit(); // 提交事务
          session.close(); // 关闭session
     }

     @Test
     public void testFetch1(){
         List<Class> classList=session.createQuery("from Class").list();
         Iterator it=classList.iterator();
         Class c1=(Class)it.next();
         Class c2=(Class)it.next();
         Class c3=(Class)it.next();
         c1.getStudents().iterator();
         c2.getStudents().iterator();
         c3.getStudents().iterator();
     }

 }

运行结果显示：

Hibernate: select class0_.classId as classId1_0_, class0_.className as classNam2_0_ from t_class class0_
Hibernate: select students0_.classId as classId3_0_1_, students0_.stuId as stuId1_1_1_, students0_.stuId as stuId1_1_0_, students0_.stuName as stuName2_1_0_, students0_.classId as classId3_1_0_ from t_student students0_ where students0_.classId in (select class0_.classId from t_class class0_)

3，Fetch:join 迫切左外连接查询方式；

Class.hbm.xml

 <?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="com.wishwzp.model">

     <class name="Class" table="t_class">
         <id name="id" column="classId">
             <generator class="native"></generator>
         </id>

         <property name="name" column="className"></property>

         <set name="students" cascade="delete" inverse="true" lazy="false" batch-size="2" fetch="join">
             <key column="classId"></key>
             <one-to-many class="com.wishwzp.model.Student"/>
         </set>
     </class>

 </hibernate-mapping>

StudentTest.java

 package com.wishwzp.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.wishwzp.model.Class;
 import com.wishwzp.model.Student;
 import com.wishwzp.util.HibernateUtil;

 public class StudentTest {

     private SessionFactory sessionFactory=HibernateUtil.getSessionFactory();
     private Session session;

     @Before
     public void setUp() throws Exception {
         session=sessionFactory.openSession(); // 生成一个session
         session.beginTransaction(); // 开启事务
     }

     @After
     public void tearDown() throws Exception {
          session.getTransaction().commit(); // 提交事务
          session.close(); // 关闭session
     }

     @Test
     public void testFetch2(){
         Class c=(Class)session.get(Class.class, Long.valueOf(1));
     }
 }

运行结果显示：

Hibernate: select class0_.classId as classId1_0_0_, class0_.className as classNam2_0_0_, students1_.classId as classId3_0_1_, students1_.stuId as stuId1_1_1_, students1_.stuId as stuId1_1_2_, students1_.stuName as stuName2_1_2_, students1_.classId as classId3_1_2_ from t_class class0_ left outer join t_student students1_ on class0_.classId=students1_.classId where class0_.classId=?

---

END