Java Tutorial/Hibernate/Projections

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AVG Projection

File: Main.java



   <source lang="java">

import java.util.Date; import java.util.List; import org.hibernate.Criteria; import org.hibernate.Session; import org.hibernate.criterion.ProjectionList; import org.hibernate.criterion.Projections; public class Main { 

 public static void main(String[] args) throws Exception {
   HibernateUtil hibernateUtil = new HibernateUtil();
   hibernateUtil
       .executeSQLCommand("create table survey (id int,name varchar, purchasedate date);");
   Session session = hibernateUtil.getSession();
   Survey survey = new Survey();
   survey.setName("Survey");
   survey.setPurchaseDate(new Date());
   session.save(survey);
   
   survey = new Survey();
   survey.setName("Survey1");
   survey.setPurchaseDate(new Date());    
   session.save(survey);
   
   session.flush();
   
   Criteria crit = session.createCriteria(Survey.class);
   ProjectionList projList = Projections.projectionList();
   projList.add(Projections.avg("Id"));
   crit.setProjection(projList);
   
   
   List results = crit.list();
   System.out.println(results);
   
   session.close();
   hibernateUtil.checkData("select * from survey");
 }

}</source>





Group Field

File: Main.java



   <source lang="java">

import java.util.Date; import java.util.List; import org.hibernate.Criteria; import org.hibernate.Session; import org.hibernate.criterion.ProjectionList; import org.hibernate.criterion.Projections; public class Main { 

 public static void main(String[] args) throws Exception {
   HibernateUtil hibernateUtil = new HibernateUtil();
   hibernateUtil
       .executeSQLCommand("create table survey (id int,name varchar, purchasedate date);");
   Session session = hibernateUtil.getSession();
   Survey survey = new Survey();
   survey.setName("Survey");
   survey.setPurchaseDate(new Date());
   session.save(survey);
   
   survey = new Survey();
   survey.setName("Survey1");
   survey.setPurchaseDate(new Date());    
   session.save(survey);
   
   session.flush();
   
   Criteria crit = session.createCriteria(Survey.class);
   ProjectionList projList = Projections.projectionList();
   projList.add(Projections.groupProperty("id"));
   projList.add(Projections.property("id"));
   crit.setProjection(projList);
   
   
   List results = crit.list();
   System.out.println(results);
   
   session.close();
   hibernateUtil.checkData("select * from survey");
 }

}</source>





Hibernate demo code from Hibernate in action

Projection: Count Distinct

File: Main.java



   <source lang="java">

import java.util.Date; import java.util.List; import org.hibernate.Criteria; import org.hibernate.Session; import org.hibernate.criterion.ProjectionList; import org.hibernate.criterion.Projections; public class Main { 

 public static void main(String[] args) throws Exception {
   HibernateUtil hibernateUtil = new HibernateUtil();
   hibernateUtil
       .executeSQLCommand("create table survey (id int,name varchar, purchasedate date);");
   Session session = hibernateUtil.getSession();
   Survey survey = new Survey();
   survey.setName("Survey");
   survey.setPurchaseDate(new Date());
   session.save(survey);
   
   survey = new Survey();
   survey.setName("Survey1");
   survey.setPurchaseDate(new Date());    
   session.save(survey);
   
   session.flush();
   
   Criteria crit = session.createCriteria(Survey.class);
   ProjectionList projList = Projections.projectionList();
   projList.add(Projections.countDistinct("Id"));
   crit.setProjection(projList);
   
   
   List results = crit.list();
   System.out.println(results);
   
   session.close();
   hibernateUtil.checkData("select * from survey");
 }

}</source>





Projection: Max

File: Main.java



   <source lang="java">

import java.util.Date; import java.util.List; import org.hibernate.Criteria; import org.hibernate.Session; import org.hibernate.criterion.ProjectionList; import org.hibernate.criterion.Projections; public class Main { 

 public static void main(String[] args) throws Exception {
   HibernateUtil hibernateUtil = new HibernateUtil();
   hibernateUtil
       .executeSQLCommand("create table survey (id int,name varchar, purchasedate date);");
   Session session = hibernateUtil.getSession();
   Survey survey = new Survey();
   survey.setName("Survey");
   survey.setPurchaseDate(new Date());
   session.save(survey);
   
   survey = new Survey();
   survey.setName("Survey1");
   survey.setPurchaseDate(new Date());    
   session.save(survey);
   
   session.flush();
   
   Criteria crit = session.createCriteria(Survey.class);
   ProjectionList projList = Projections.projectionList();
   projList.add(Projections.max("Id"));
   crit.setProjection(projList);
   
   
   List results = crit.list();
   System.out.println(results);
   
   session.close();
   hibernateUtil.checkData("select * from survey");
 }

}</source>





Projection: Min

File: Main.java



   <source lang="java">

import java.util.Date; import java.util.List; import org.hibernate.Criteria; import org.hibernate.Session; import org.hibernate.criterion.ProjectionList; import org.hibernate.criterion.Projections; public class Main { 

 public static void main(String[] args) throws Exception {
   HibernateUtil hibernateUtil = new HibernateUtil();
   hibernateUtil
       .executeSQLCommand("create table survey (id int,name varchar, purchasedate date);");
   Session session = hibernateUtil.getSession();
   Survey survey = new Survey();
   survey.setName("Survey");
   survey.setPurchaseDate(new Date());
   session.save(survey);
   
   survey = new Survey();
   survey.setName("Survey1");
   survey.setPurchaseDate(new Date());    
   session.save(survey);
   
   session.flush();
   
   Criteria crit = session.createCriteria(Survey.class);
   ProjectionList projList = Projections.projectionList();
   projList.add(Projections.min("Id"));
   crit.setProjection(projList);
   
   
   List results = crit.list();
   System.out.println(results);
   
   session.close();
   hibernateUtil.checkData("select * from survey");
 }

}</source>





Scalar SQL Query

File: Main.java



   <source lang="java">

import java.util.List; import org.hibernate.Hibernate; import org.hibernate.SQLQuery; import org.hibernate.Session; public class Main { 

 public static void main(String[] args) throws Exception {
   HibernateUtil hibernateUtil = new HibernateUtil();
   hibernateUtil
       .executeSQLCommand("create table Product(id int, name varchar, description varchar, price decimal(6,2), supplierid int)");
    
   hibernateUtil
   .executeSQLCommand("create table Supplier (id int , name varchar)");
   hibernateUtil
   .executeSQLCommand("create table Software(id int, name varchar, description varchar, price decimal(6,2), supplierid int, version varchar)");
   
   Session session = hibernateUtil.getSession();
   Supplier superCorp = new Supplier();
   superCorp.setName("Supplier1");
   session.save(superCorp);
   
   Supplier megaInc = new Supplier();
   megaInc.setName("Supplier2");
   session.save(megaInc);        
   Product mouse = new Product("Product1","first product", 20.0);
   mouse.setSupplier(superCorp);
   superCorp.getProducts().add(mouse);
   session.flush();
   Product mouse2 = new Product("Product2","second product", 22.0);
   mouse2.setSupplier(superCorp);
   superCorp.getProducts().add(mouse2);        
   
   Product keyboard = new Product("Product3", "third product", 30.0);
   keyboard.setSupplier(megaInc);
   megaInc.getProducts().add(keyboard);
   Software webBrowser = new Software("Web Browser","new browser", 75.0, "2.0");
   webBrowser.setSupplier(superCorp);
   superCorp.getProducts().add(webBrowser);
   Software email = new Software("Email","email client", 49.99, "4.1 Edition");
   email.setSupplier(megaInc);
   megaInc.getProducts().add(email);    
   session.flush();
   
   
   
   String sql = "select avg(product.price) as avgPrice from Product product";
   
   SQLQuery query = session.createSQLQuery(sql);
   query.addScalar("avgPrice",Hibernate.DOUBLE);
   List results = query.list();
   System.out.println(results);
   
   
   
   session.close();
   hibernateUtil.checkData("select * from Product");
   hibernateUtil.checkData("select * from Software");
   hibernateUtil.checkData("select * from Supplier");
 }

}</source>





Select Specific Fields in a Entity with Criteria and Projections

File: Main.java



   <source lang="java">

import java.util.Date; import java.util.List; import org.hibernate.Criteria; import org.hibernate.Session; import org.hibernate.criterion.ProjectionList; import org.hibernate.criterion.Projections; public class Main { 

 public static void main(String[] args) throws Exception {
   HibernateUtil hibernateUtil = new HibernateUtil();
   hibernateUtil
       .executeSQLCommand("create table survey (id int,name varchar, purchasedate date);");
   Session session = hibernateUtil.getSession();
   Survey survey = new Survey();
   survey.setName("Survey");
   survey.setPurchaseDate(new Date());
   session.save(survey);
   
   survey = new Survey();
   survey.setName("Survey1");
   survey.setPurchaseDate(new Date());    
   session.save(survey);
   
   session.flush();
   
   Criteria crit = session.createCriteria(Survey.class);
   ProjectionList projList = Projections.projectionList();
   projList.add(Projections.property("Id"));
   projList.add(Projections.property("name"));
   crit.setProjection(projList);
   
   
   List results = crit.list();
   System.out.println(results);
   
   session.close();
   hibernateUtil.checkData("select * from survey");
 }

}</source>


Источник — «http://jexp.ru/index.php?title=Java_Tutorial/Hibernate/Projections&oldid=4502»