关于HQL查询,我们可以结合hibernate的API文档,重点围绕org.hibernate.Query接口,分析其方法,此接口的实例对象是通过通过session、对象的creatQuery(String hql)方法得到的。我这里要分析HQL的select子句,当然要想深入HQL查询,我们就必须了解hibernate缓存的知识。
一、选择——Select子句查询返回对象的讨论
为什么只说Select子句,因为我们使用的hibernate框架是基于java语言环境下进行开发的,也就是说hibernate是将数据库进行了对象化,那么我们使用Select语句查询到的记录,返回的是什么对象,这个很让人感兴趣。
首先我们看看在只是用from子句的情况:
package com.third; import java.util.Iterator; import java.util.List; import org.hibernate.Query; import org.hibernate.ScrollableResults; import org.hibernate.Session; import org.hibernate.SessionFactory; import org.hibernate.Transaction; import org.hibernate.cfg.Configuration; import org.hibernate.service.ServiceRegistry; import org.hibernate.service.ServiceRegistryBuilder; import org.junit.After; import org.junit.Before; import org.junit.Test; import com.third.Dao2.Students2; public class Test3 { private static SessionFactory sessionFactory; private static Session session; private static Transaction transaction; @Before public void init(){ //先获取配置对象,匹配hibernate.cfg.xml文件 Configuration config=new Configuration().configure(); //获取注册服务对象(该对象中包含hibernate.cfg.xml中的<properties>和<maping>信息 ServiceRegistry serviceRegistry=new ServiceRegistryBuilder().applySettings(config.getProperties()).buildServiceRegistry(); //获取sessionFactory对象,通过sessionFactory对象读取hibernate.cfg.xml文档信息,并通过<mapping>标签加载hbm.xml文件信息 sessionFactory=config.buildSessionFactory(serviceRegistry); } @Test public void test3(){ //通过sessionFactory对象获取session对象 session=sessionFactory.openSession(); //通过session对象开启事务,并且返回事务(transaction)对象 transaction=session.beginTransaction(); //创建HQL语句用于后面的查询需要,需要查询Students2类 String hql="from Students2"; Query query=session.createQuery(hql); List<Students2> students=query.list(); for (Students2 students2 : students) { System.out.println("学号:"+students2.getSid() +" 姓别:"+students2.getSgender()+" 姓名:"+students2.getSname()); } } @After public void destory(){ transaction.commit(); //关闭开启的资源 if(session!=null){ session.close(); } if(sessionFactory!=null){ sessionFactory.close(); } }
我们能够看到上述代码中绿色背景的代码,说明查询对象query通过list()方法返回查询对象query的查询结果返回的是一个list集合且其泛型是Students2,也就是说只是用from子句查询返回的对象可以用Students类对象的集合接收,这个很好理解,你查的是Students2类在session中的所有实例对象的所有信息(这些对象和数据库中的students2表格记录一一对应),这个很合理。但是,如果我们使用Select语句,我们查询的Students2类在session中的实例对象的部分信息,那么返回的是什么对象?很显然,肯定不再是返回Students2类的对象。
我们看看下面的代码:用select语句挑选students2类的部分属性查询,强行用Students2对象接收返回的结果~
package com.third; import java.util.Iterator; import java.util.List; import org.hibernate.Query; import org.hibernate.ScrollableResults; import org.hibernate.Session; import org.hibernate.SessionFactory; import org.hibernate.Transaction; import org.hibernate.cfg.Configuration; import org.hibernate.service.ServiceRegistry; import org.hibernate.service.ServiceRegistryBuilder; import org.junit.After; import org.junit.Before; import org.junit.Test; import com.third.Dao2.Students2; public class Test3 { private static SessionFactory sessionFactory; private static Session session; private static Transaction transaction; @Before public void init(){ //先获取配置对象,匹配hibernate.cfg.xml文件 Configuration config=new Configuration().configure(); //获取注册服务对象(该对象中包含hibernate.cfg.xml中的<properties>和<maping>信息 ServiceRegistry serviceRegistry=new ServiceRegistryBuilder().applySettings(config.getProperties()).buildServiceRegistry(); //获取sessionFactory对象,通过sessionFactory对象读取hibernate.cfg.xml文档信息,并通过<mapping>标签加载hbm.xml文件信息 sessionFactory=config.buildSessionFactory(serviceRegistry); } @Test public void test3(){ //通过sessionFactory对象获取session对象 session=sessionFactory.openSession(); //通过session对象开启事务,并且返回事务(transaction)对象 transaction=session.beginTransaction(); //创建HQL语句用于后面的查询需要 //查询单条记录的sid和sname信息(hql语句) String hql="select sid,sname,sgender from Students2 where sid=1";//创建单挑记录查询对象query Query query=session.createQuery(hql); 54 List<Students2> list=query.list(); for (Students2 students2 : list) { System.out.println("学号:"+students2.getSid()+" 姓名:"+students2.getSname()); } } @After public void destory(){ transaction.commit(); //关闭开启的资源 if(session!=null){ session.close(); } if(sessionFactory!=null){ sessionFactory.close(); } } }
运行代码之后:junit运行不通过,抛出异常:
java.lang.ClassCastException: [Ljava.lang.Object; cannot be cast to com.third.Dao2.Students2 at com.third.Test3.test3(Test3.java:54) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:606) at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:45) at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:15) at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:42) at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:20) at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:28) at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:30) at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:263) at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:68) at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:47) at org.junit.runners.ParentRunner$3.run(ParentRunner.java:231) at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:60) at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:229) at org.junit.runners.ParentRunner.access$000(ParentRunner.java:50) at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:222) at org.junit.runners.ParentRunner.run(ParentRunner.java:300) at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:86) at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:459) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:675) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:382) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:192)
我们重点看被我用绿色背景加重的错误报文,
java.lang.ClassCastException: [Ljava.lang.Object; cannot be cast to com.third.Dao2.Students2 at com.third.Test3.test3(Test3.java:54)
大概意思是:程序在Test3.java的54行执行出现错误,即List<Students2> list=query.list();这行代码执行不了了,出现的错误是:java.lang.Object[]类对象没法映射到com.third.Dao2.Students2类对象中。
分析原因:
很明显通过query.list()方法返回的对象是Object[]类型单个个体或者集合,也就是说将数据库表格的每条记录的每个字段信息映以Object类对象的形式返回,而每条记录就是以一个Object[]类(Object类对象数组)对象返回,所有记录被封装在一个list集合中。也就是说使用select子句的HQL查询语句,查询表格记录返回的对象类型是Object[]。
二、没有select子句的from子句查询对象讨论
之前我们说过只有from子句,查询表格记录返回的对象可以用查询类(Students类)对象的集合接收,并没有指出到底返回的对象是什么类型。然后我们开始思考没有select子句,只有from子句的查询,查询表格记录返回的对象类型到底是什么?
我们开始尝试使用List<Object[]> list=query.list();即使用Object[]来接受只有from子句的HQL查询表格记录返回的对象:
1 package com.third; 2 3 import java.util.List; 4 5 import org.hibernate.Query; 6 import org.hibernate.Session; 7 import org.hibernate.SessionFactory; 8 import org.hibernate.Transaction; 9 import org.hibernate.cfg.Configuration; 10 import org.hibernate.service.ServiceRegistry; 11 import org.hibernate.service.ServiceRegistryBuilder; 12 import org.junit.After; 13 import org.junit.Before; 14 import org.junit.Test; 15 16 import com.third.Dao2.Students2; 17 18 public class Test3 { 19 private static SessionFactory sessionFactory; 20 private static Session session; 21 private static Transaction transaction; 22 @Before 23 public void init(){ 24 //先获取配置对象,匹配hibernate.cfg.xml文件 25 Configuration config=new Configuration().configure(); 26 //获取注册服务对象(该对象中包含hibernate.cfg.xml中的<properties>和<maping>信息 27 ServiceRegistry serviceRegistry=new ServiceRegistryBuilder().applySettings(config.getProperties()).buildServiceRegistry(); 28 //获取sessionFactory对象,通过sessionFactory对象读取hibernate.cfg.xml文档信息,并通过<mapping>标签加载hbm.xml文件信息 29 sessionFactory=config.buildSessionFactory(serviceRegistry); 30 } 31 32 @Test 33 public void test3(){ 34 //通过sessionFactory对象获取session对象 35 session=sessionFactory.openSession(); 36 //通过session对象开启事务,并且返回事务(transaction)对象 37 transaction=session.beginTransaction(); 38 39 //创建HQL语句用于后面的查询需要 40 //查询所有记录的sid和sname信息(hql语句) 41 String hql=" from Students2"; 42 43 //创建多条记录查询对象query1 44 Query query=session.createQuery(hql); 45 46 List<Object[]> list=query.list(); 47 for (Object[] objects : list) { 48 System.out.println("学号:"+objects[0]+" 姓名:"+objects[1]+" 性别:"+objects[2]); 49 } 50 51 } 52 53 @After 54 public void destory(){ 55 transaction.commit(); 56 //关闭开启的资源 57 if(session!=null){ 58 session.close(); 59 } 60 if(sessionFactory!=null){ 61 sessionFactory.close(); 62 } 63 } 64 }
使用junit调试后,抛出异常:
java.lang.ClassCastException: com.third.Dao2.Students2 cannot be cast to [Ljava.lang.Object; at com.third.Test3.test3(Test3.java:47) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:606) at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:45) at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:15) at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:42) at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:20) at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:28) at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:30) at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:263) at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:68) at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:47) at org.junit.runners.ParentRunner$3.run(ParentRunner.java:231) at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:60) at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:229) at org.junit.runners.ParentRunner.access$000(ParentRunner.java:50) at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:222) at org.junit.runners.ParentRunner.run(ParentRunner.java:300) at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:86) at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:459) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:675) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:382) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:192)
我们重点分析绿色背景的错误报文
java.lang.ClassCastException: com.third.Dao2.Students2 cannot be cast to [Ljava.lang.Object; at com.third.Test3.test3(Test3.java:46)
大概意思是:程序在Test3.java的46行执行出现错误,即List<Object[]> list=query.list();这行代码执行不了了,出现的错误是:com.third.Dao2.Students2类对象没法映射到java.lang.Object[]类对象中。
这个就很戏剧化了,正好和使用select子句的情况相反。这就说明只有from子句的HQL查询,查询表格记录返回的对象是查询类对象(com.third.Dao2.Students2类对象)。
三、给出几种正确的select查询处理方法:
1、以Object[]形式返回
select子句中未指定返回数据类型,默认为Object[].
代码示例:
1 package com.third; 2 3 import java.util.Iterator; 4 import java.util.List; 5 6 import org.hibernate.Query; 7 import org.hibernate.ScrollableResults; 8 import org.hibernate.Session; 9 import org.hibernate.SessionFactory; 10 import org.hibernate.Transaction; 11 import org.hibernate.cfg.Configuration; 12 import org.hibernate.service.ServiceRegistry; 13 import org.hibernate.service.ServiceRegistryBuilder; 14 import org.junit.After; 15 import org.junit.Before; 16 import org.junit.Test; 17 18 import com.third.Dao2.Students2; 19 20 public class Test3 { 21 private static SessionFactory sessionFactory; 22 private static Session session; 23 private static Transaction transaction; 24 @Before 25 public void init(){ 26 //先获取配置对象,匹配hibernate.cfg.xml文件 27 Configuration config=new Configuration().configure(); 28 //获取注册服务对象(该对象中包含hibernate.cfg.xml中的<properties>和<maping>信息 29 ServiceRegistry serviceRegistry=new ServiceRegistryBuilder().applySettings(config.getProperties()).buildServiceRegistry(); 30 //获取sessionFactory对象,通过sessionFactory对象读取hibernate.cfg.xml文档信息,并通过<mapping>标签加载hbm.xml文件信息 31 sessionFactory=config.buildSessionFactory(serviceRegistry); 32 } 33 34 @Test 35 public void test3(){ 36 //通过sessionFactory对象获取session对象 37 session=sessionFactory.openSession(); 38 //通过session对象开启事务,并且返回事务(transaction)对象 39 transaction=session.beginTransaction(); 40 41 //创建HQL语句用于后面的查询需要 42 //查询所有记录的sid和sname信息(hql语句) 43 String hql1="select sid,sname from Students2 "; 44 //创建多条记录查询对象query1 45 Query query1=session.createQuery(hql1); 46 47 List<Object[]> list1=query1.list(); 48 for (Object[] objects : list1) { 49 System.out.println("学号:"+objects[0]+" 姓名:"+objects[1]); 50 } 51 52 /*Iterator<Students2> it=query.iterate(); 53 while(it.hasNext()){ 54 Students2 stu=it.next(); 55 System.out.println("学号:"+stu.getSid() 56 +" 姓别:"+stu.getSgender()+" 姓名:"+stu.getSname()); 57 }*/ 58 59 } 60 61 @After 62 public void destory(){ 63 transaction.commit(); 64 //关闭开启的资源 65 if(session!=null){ 66 session.close(); 67 } 68 if(sessionFactory!=null){ 69 sessionFactory.close(); 70 } 71 } 72 }
2、以List形式返回
select子句使用new List指定
1 package com.third; 2 3 import java.util.Iterator; 4 import java.util.List; 5 6 import org.hibernate.Query; 7 import org.hibernate.ScrollableResults; 8 import org.hibernate.Session; 9 import org.hibernate.SessionFactory; 10 import org.hibernate.Transaction; 11 import org.hibernate.cfg.Configuration; 12 import org.hibernate.service.ServiceRegistry; 13 import org.hibernate.service.ServiceRegistryBuilder; 14 import org.junit.After; 15 import org.junit.Before; 16 import org.junit.Test; 17 18 import com.third.Dao2.Students2; 19 20 public class Test3 { 21 private static SessionFactory sessionFactory; 22 private static Session session; 23 private static Transaction transaction; 24 @Before 25 public void init(){ 26 //先获取配置对象,匹配hibernate.cfg.xml文件 27 Configuration config=new Configuration().configure(); 28 //获取注册服务对象(该对象中包含hibernate.cfg.xml中的<properties>和<maping>信息 29 ServiceRegistry serviceRegistry=new ServiceRegistryBuilder().applySettings(config.getProperties()).buildServiceRegistry(); 30 //获取sessionFactory对象,通过sessionFactory对象读取hibernate.cfg.xml文档信息,并通过<mapping>标签加载hbm.xml文件信息 31 sessionFactory=config.buildSessionFactory(serviceRegistry); 32 } 33 34 @Test 35 public void test3(){ 36 //通过sessionFactory对象获取session对象 37 session=sessionFactory.openSession(); 38 //通过session对象开启事务,并且返回事务(transaction)对象 39 transaction=session.beginTransaction(); 40 41 //创建HQL语句用于后面的查询需要 42 //查询所有记录的sid和sname信息(hql语句) 43 String hql1="select new list(sid,sname) from Students2 "; 44 //创建多条记录查询对象query1 45 Query query1=session.createQuery(hql1); 46 47 List<List> list1=query1.list(); 48 for (List list : list1) { 49 System.out.println("学号:"+list.get(0)+" 姓名:"+list.get(1)); 50 } 51 52 } 53 54 @After 55 public void destory(){ 56 transaction.commit(); 57 //关闭开启的资源 58 if(session!=null){ 59 session.close(); 60 } 61 if(sessionFactory!=null){ 62 sessionFactory.close(); 63 } 64 } 65 }
首先我们来分析其中的HQL语句select new list(sid,sname) from Students2 其中new list(sid,,sname)直接指定了查询返回的是list集合。如果我们在这里强行使用其他的对象类型来接受返回的对象,会出现什么?
我们可以看一下下面的情况(稍微修改了接收对象类型):
//查询所有记录的sid和sname信息(hql语句) String hql1="select new list(sid,sname) from Students2 "; //创建多条记录查询对象query1 Query query1=session.createQuery(hql1); 50 List<Object[]> list1=query1.list(); for (Object[] objects : list1) { System.out.println("学号:"+objects[0]+" 姓名:"+objects[1]); }
运行程序时抛出异常:
java.lang.ClassCastException: java.util.Arrays$ArrayList cannot be cast to [Ljava.lang.Object; at com.third.Test3.test3(Test3.java:50) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:606) at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:45) at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:15) at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:42) at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:20) at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:28) at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:30) at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:263) at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:68) at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:47) at org.junit.runners.ParentRunner$3.run(ParentRunner.java:231) at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:60) at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:229) at org.junit.runners.ParentRunner.access$000(ParentRunner.java:50) at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:222) at org.junit.runners.ParentRunner.run(ParentRunner.java:300) at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:86) at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:459) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:675) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:382) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:192)
我们重点看这两句错误报文:
java.lang.ClassCastException: java.util.Arrays$ArrayList cannot be cast to [Ljava.lang.Object;
at com.third.Test3.test3(Test3.java:50)
程序在Test3.java的50行执行出现错误,即List<Obiect[]>
list=query.list();这行代码执行不了了,出现的错误是: java.util.Arrays$ArrayList类对象没法映射到java.lang.Object[]类对象中。
这里我们可以的到一个结论:HQL语句通过new list(...)方式查询,查询对象query通过list()方法返回的list集合内对象类型是java.util.Arrays$ArrayList,并且表格的记录最终的查询信息对象,只能使用list对象去接收。
3、以Map形式返回
select子句使用new
map指定,这里特别要注意map是以键值对形式储存,所以其get()方法中势必可以存储属性名,我们可以通过get(string
name)方法读取信息。所以读取查询结果时我们有两种方式。然后其他的内容和new list相似,不在过多赘述了。
代码示例:
1 package com.third; 2 3 import java.lang.reflect.Field; 4 import java.util.Iterator; 5 import java.util.List; 6 import java.util.Map; 7 8 import org.hibernate.Query; 9 import org.hibernate.ScrollableResults; 10 import org.hibernate.Session; 11 import org.hibernate.SessionFactory; 12 import org.hibernate.Transaction; 13 import org.hibernate.cfg.Configuration; 14 import org.hibernate.service.ServiceRegistry; 15 import org.hibernate.service.ServiceRegistryBuilder; 16 import org.junit.After; 17 import org.junit.Before; 18 import org.junit.Test; 19 20 import com.third.Dao2.Students2; 21 22 public class Test3 { 23 private static SessionFactory sessionFactory; 24 private static Session session; 25 private static Transaction transaction; 26 @Before 27 public void init(){ 28 //先获取配置对象,匹配hibernate.cfg.xml文件 29 Configuration config=new Configuration().configure(); 30 //获取注册服务对象(该对象中包含hibernate.cfg.xml中的<properties>和<maping>信息 31 ServiceRegistry serviceRegistry=new ServiceRegistryBuilder().applySettings(config.getProperties()).buildServiceRegistry(); 32 //获取sessionFactory对象,通过sessionFactory对象读取hibernate.cfg.xml文档信息,并通过<mapping>标签加载hbm.xml文件信息 33 sessionFactory=config.buildSessionFactory(serviceRegistry); 34 } 35 36 @Test 37 public void test3(){ 38 //通过sessionFactory对象获取session对象 39 session=sessionFactory.openSession(); 40 //通过session对象开启事务,并且返回事务(transaction)对象 41 transaction=session.beginTransaction(); 42 43 //创建HQL语句用于后面的查询需要 44 //查询所有记录的sid和sname信息(hql语句) 45 String hql="select new map(sid ,sname) from Students2"; 46 String hql1="select new map(sid as id,sname as name) from Students2 "; 47 48 //创建多条记录查询对象query1 49 Query query=session.createQuery(hql); 50 Query query1=session.createQuery(hql1); 51 List<Map> list=query.list(); 52 List<Map> list1=query1.list(); 53 for (Map map : list) { 54 System.out.println("学号:"+map.get("0")+" 姓名:"+map.get("1")); 55 } 56 System.out.println("*******************"); 57 for (Map map : list1) { 58 System.out.println("学号:"+map.get("id")+" 姓名:"+map.get("name")); 59 } 60 61 62 } 63 64 @After 65 public void destory(){ 66 transaction.commit(); 67 //关闭开启的资源 68 if(session!=null){ 69 session.close(); 70 } 71 if(sessionFactory!=null){ 72 sessionFactory.close(); 73 } 74 } 75 }
4、以自定义类型返回
(1)持久化类中定义对应的构造器
(2)select子句中调用定义的构造器
首先我们需要要查询类(持久化类中添加相应的构造函数)
Students2.java
package com.third.Dao2; import java.io.Serializable; import java.util.HashSet; import java.util.Set; public class Students2 implements Serializable { private int sid; private String sname; private String sgender; private Set<Teachers> teaList=new HashSet<Teachers>(); public Students2(int sid, String sname) { this.sid = sid; this.sname = sname; } public Students2() { } public int getSid() { return sid; } public void setSid(int sid) { this.sid = sid; } public String getSname() { return sname; } public void setSname(String sname) { this.sname = sname; } public String getSgender() { return sgender; } public void setSgender(String sgender) { this.sgender = sgender; } public Set<Teachers> getTeaList() { return teaList; } public void setTeaList(Set<Teachers> teaList) { this.teaList = teaList; } }
1 package com.third; 2 3 import java.util.List; 4 5 import org.hibernate.Query; 6 import org.hibernate.Session; 7 import org.hibernate.SessionFactory; 8 import org.hibernate.Transaction; 9 import org.hibernate.cfg.Configuration; 10 import org.hibernate.service.ServiceRegistry; 11 import org.hibernate.service.ServiceRegistryBuilder; 12 import org.junit.After; 13 import org.junit.Before; 14 import org.junit.Test; 15 16 import com.third.Dao2.Students2; 17 18 public class Test3 { 19 private static SessionFactory sessionFactory; 20 private static Session session; 21 private static Transaction transaction; 22 @Before 23 public void init(){ 24 //先获取配置对象,匹配hibernate.cfg.xml文件 25 Configuration config=new Configuration().configure(); 26 //获取注册服务对象(该对象中包含hibernate.cfg.xml中的<properties>和<maping>信息 27 ServiceRegistry serviceRegistry=new ServiceRegistryBuilder().applySettings(config.getProperties()).buildServiceRegistry(); 28 //获取sessionFactory对象,通过sessionFactory对象读取hibernate.cfg.xml文档信息,并通过<mapping>标签加载hbm.xml文件信息 29 sessionFactory=config.buildSessionFactory(serviceRegistry); 30 } 31 32 @Test 33 public void test3(){ 34 //通过sessionFactory对象获取session对象 35 session=sessionFactory.openSession(); 36 //通过session对象开启事务,并且返回事务(transaction)对象 37 transaction=session.beginTransaction(); 38 39 //创建HQL语句用于后面的查询需要 40 //查询所有记录的sid和sname信息(hql语句) 41 String hql="select new Students2(sid ,sname) from Students2"; 42 43 //创建多条记录查询对象query1 44 Query query=session.createQuery(hql); 45 46 List<Students2> list=query.list(); 47 48 for (Students2 stu : list) { 49 System.out.println("学号:"+stu.getSid()+" 姓名:"+stu.getSname()); 50 } 59 } 60 61 @After 62 public void destory(){ 63 transaction.commit(); 64 //关闭开启的资源 65 if(session!=null){ 66 session.close(); 67 } 68 if(sessionFactory!=null){ 69 sessionFactory.close(); 70 } 71 } 72 }
其他的主要内容和new list方式一样。
四、总结:
1、没有select子句有from子句的HQL查询,查询表格的记录,返回的对象是查询类对象;即List<查询类名> list=query.list();
2、有select子句的HQL查询,查询表格记录,返回的对象是Object[]类对象,即List<Object[]> lsit=query.lsit();
3、我们可以通过在HQL语句中使用new list(...),new map(...),new Students2(...)的方式来指定查询返回的对象类型。
4、使用new Students2(...)的方式,即以自定义类型返回的方式,需要在该查询类的持久化类Students2.java中添加相应的构造函数。