hibernate5-projection queries, group queries, query list and iterate

1. Create project, project name HIBERNATEDEMO9, directory structure

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2. Create a Lib directory storage jar file in the project, directory structure

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3. Create the entity Bean Forum, package name (Com.mycompany.demo.bean) in the SRC directory,

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4. Entity Bean Forum content is as follows

Package com.mycompany.demo.bean;public class forum {private int fid;private  string name;private int isshow;public int getisshow ()  {return isshow;} Public void setisshow (Int isshow)  {this.isshow = isshow;} Public forum ()  {super ();} Public forum (String name)  {super (); this.name = name;} Public int getfid ()  {return fid;} Public void setfid (Int fid)  {this.fid = fid;} Public string getname ()  {return name;} Public void setname (String name)  {this.name = name;} @Overridepublic  int hashcode ()  {final int prime = 31;int result =  1;result = prime * result + fid;result = prime *  result +  ((Name == null)  ? 0 : name.hashcode ()); Return rEsult;} @Overridepublic  boolean equals (object obj)  {if  (this == obj) return  true;if  (obj == null) return false;if  (GetClass ()  != obj.getclass ()) return  false; forum other =  (Forum)  obj;if  (Fid != other.fid) return false;if  ( Name == null)  {if  (Other.name != null) Return false;}  else if  (!name.equals (other.name)) return false;return true;}

5. In the SRC directory, create the Entity Bean Forum Mapping file Forum.hbm.xml, package name (Com.mycompany.demo.bean),

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6. The contents of the mapping file Forum.hbm.xml are as follows

<?xml version= "1.0"  encoding= "Utf-8"? ><! doctype hibernate-mapping public   "-//hibernate/hibernate mapping dtd//en"   "HTTP://WWW.HIBERNATE.ORG/DTD/HIBERNATE-MAPPING-3.0.DTD" > <!--Package: Specify <class/> packages to be located    -->

7. Create the tool class Hbnutil, package name (com.mycompany.demo.util) in the SRC directory,
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8. The contents of the tool class Hbnutil are as follows
Package Com.mycompany.demo.util;import Org.hibernate.session;import Org.hibernate.sessionfactory;import Org.hibernate.cfg.configuration;public class Hbnutil {private static sessionfactory sessionfactory;public static Session getsession () {if (sessionfactory = = NULL | | sessionfactory.isclosed ()) {sessionfactory = new Configuration (). Configure (). Buildsessionfactory ();} return sessionfactory.getcurrentsession ();}}

9. Create the Hibernate profile Hibernate.cfg.xml in the SRC directory,
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The contents of the 10.Hibernate configuration file Hibernate.cfg.xml are as follows
<?xml version= "1.0"  encoding= "Utf-8"? ><! doctype hibernate-configuration system  "http://www.hibernate.org/dtd/ Hibernate-configuration-3.0.dtd ">

11. Create the test directory in the project to store testing files, file name Manageforum, package name (Com.mycompany.demo.bean), directory structure
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The contents of the 12.ManageForum test class are as follows
package com.mycompany.demo.bean;import java.util.iterator;import java.util.list;import  org.hibernate.hibernateexception;import org.hibernate.session;import  org.hibernate.criterion.projectionlist;import org.hibernate.criterion.projections;import  org.hibernate.transform.transformers;import org.junit.before;import org.junit.test;import  com.mycompany.demo.util.hbnutil;public class manageforum {private session session;@ Beforepublic void init () {session = hbnutil.getsession ();} /* *  projection Query-sql */@Testpublic  void testprojectionsql () {try { Session.begintransaction (); string sql =  "Select fid,name from hnsq_forum"; List<forum> forums = session.createsqlquery (SQL). Setresulttransformer ( Transformers.aliastobean (Forum.class)). List ();for  (forum forum : forums)  { System.out.println (Forum.getname ());} SessioN.gettransaction (). commit ();}  catch  (exception e)  {session.gettransaction (). rollback (); E.printstacktrace ();}} /* *  projection Query-hql */@Testpublic  void testprojectionhql () {try { Session.begintransaction (); string sql =  "Select new forum (name)  from forum"; List<forum> forums = session.createquery (SQL). List ();for  (forum forum :  forums)  {system.out.println (Forum.getname ());} Session.gettransaction (). commit ();}  catch  (exception e)  {session.gettransaction (). rollback (); E.printstacktrace ();}} /* *  projection Query-qbc */@Testpublic  void testprojectionqbc () {try { Session.begintransaction (); Projectionlist projections = projections.projectionlist (). Add (Projections.alias ( Projections.property ("name"),  "name"). Add (Projections.alias (Projections.property ("FID"),  "FID")); List<forum> forums = session.creatEcriteria (Forum.class). Setprojection (projections). Setresulttransformer (Transformers.aliastobean (Forum.class)). List ();for  (forum forum : forums)  {system.out.println (Forum.getfid ()  + "="  + forum.getname ());} Session.gettransaction (). commit ();}  catch  (exception e)  {session.gettransaction (). rollback (); E.printstacktrace ();}} /* *  Group Query-sql */@Testpublic  void testgrounpforsql () {try { Session.begintransaction (); string sql =  "Select isshow from hnsq_forum group by isshow"; List<boolean> lists = session.createsqlquery (SQL). List ();for  (Boolean isshow  : lists)  {system.out.println (isshow);} Session.gettransaction (). commit ();}  catch  (exception e)  {session.gettransaction (). rollback (); E.printstacktrace ();}} /* *  Group Query-hql */@Testpublic  void testgrounpforhql () {Try {session.begintRansaction (); string sql =  "Select isshow from forum group by isshow"; List<object> lists = session.createquery (SQL). List ();for  (object isshow :  lists)  {system.out.println (isshow);} Session.gettransaction (). commit ();}  catch  (exception e)  {session.gettransaction (). rollback (); E.printstacktrace ();}} /* *  Group Query-qbc */@Testpublic &NBSP;VOID&NBSP;TESTGROUNPFORQBC () {try { Session.begintransaction (); List<object> lists = session.createcriteria (Forum.class). SetProjection ( Projections.groupproperty ("Isshow")). List ();for  (object isshow : lists)  { System.out.println (isshow);} Session.gettransaction (). commit ();}  catch  (hibernateexception e)  {session.gettransaction (). rollback (); E.printstacktrace ();}} /* * query list Query  * 1. All eligible records are queried at once  * 2. No caching mechanism is used, each query is fetched from the database  */@ testpublic Void testqueryforlist () {try {session.begintransaction (); string hql =  "From forum";//Output sqllist<forum> forums =  Session.createquery (HQL). List ();for  (forum forum : forums)  {system.out.println ( Forum.getname ());} Will output Sqllist<forum> forums2 = session.createquery (HQL). List ();for  (Forum forum &NBSP;:&NBSP;FORUMS2)  {system.out.println (Forum.getname ());} Session.gettransaction (). commit ();}  catch  (exception e)  {session.gettransaction (). rollback (); E.printstacktrace ();}} /* * query iterate query  * 1. The ID of all eligible records is queried, and then the specific contents of the record are queried based on the ID  * 2. Using caching mechanisms, first read from the cache, If no more data is read from the database  * 3. N+1 problem  */@Testpublic  void testqueryforiterate () {try { Session.begintransaction (); string hql =  "From forum";//Output sqliterator<forum> forums =  Session.createquery (HQL). Iterate (); while (Forums.hasnext ()) {System.out. println (Forums.next (). GetName ());} This generates the SQL for the query ID, and the other specific record information reads the data iterator<forum> forums2 = session.createquery (HQL) from the cache based on the ID. Iterate (); while (Forums2.hasnext ()) {System.out.println (Forums2.next (). GetName ());} Session.gettransaction (). commit ();}  catch  (exception e)  {session.gettransaction (). rollback (); E.printstacktrace ();}} /* *  solving n+1 problem  */@Testpublic  void testnplusone () {try {session.begintransaction () ; string hql =  "From forum";//Output Query sqllist<forum> forums =  Session.createquery (HQL). List ();for  (forum forum : forums)  {system.out.println ( Forum.getname ());} This generates the SQL for the query ID, and the other specific record information reads the data iterator<forum> forums2 = session.createquery (HQL) from the cache based on the ID. Iterate (); while (Forums2.hasnext ()) {System.out.println (Forums2.next (). GetName ());} Session.gettransaction (). commit ();}  catch  (exception e)  {session.gettransaction (). rollback (); e.printStackTrace ();}}} 
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hibernate5-projection queries, group queries, query list and iterate