Hibernate Native SQL Example

本文来自：http://hibernate.javabeat.net/tutorials/17-hibernate-native-sql-example.php

Native SQL is handwritten SQL for all database operations like create,update, delete and select. Hibernate Native Query also supports storedprocedures. Hibernate allows you to run Native SQL Query for all the databaseoperations, so you can use your existing handwritten sql with Hibernate, thisalso helps you in migrating your SQL/JDBC based application to Hibernate.

In this example we will show you how you can use Native SQL with hibernate.You will learn how to use Native to calculate average and then in anotherexample select all the objects from table.

Here is the code of Hibernate Native SQL:

import org.hibernate.Session;
import org.hibernate.*;
import org.hibernate.criterion.*;
import org.hibernate.cfg.*;
import java.util.*;
public class NativeQueryExample {
  public static void main(String[] args) {
    Session session = null;

    try{
      // This step will read hibernate.cfg.xml and prepare hibernate for use
      SessionFactory sessionFactory = new Configuration().configure().buildSessionFactory();
      session =sessionFactory.openSession();
      /* Hibernate Native Query Average Examle*/
       String sql ="select stddev(ins.invested_amount) as stdErr, "+
         " avg(ins.invested_amount) as mean "+
         " from insurance ins";
       Query query = session.createSQLQuery(sql).addScalar("stdErr",Hibernate.DOUBLE).
         addScalar("mean",Hibernate.DOUBLE);
       //Double [] amount = (Double []) query.uniqueResult(); 
       Object [] amount = (Object []) query.uniqueResult(); 
       System.out.println("mean amount: " + amount[0]);
       System.out.println("stdErr amount: " + amount[1]);

       /* Example to show Native query to select all the objects from database */
       /* Selecting all the objects from insurance table */
       List insurance = session.createSQLQuery("select  {ins.*}  from insurance ins")
      .addEntity("ins", Insurance.class)
        .list();
      for (Iterator it = insurance.iterator(); it.hasNext();) {
        Insurance insuranceObject = (Insurance) it.next();
        System.out.println("ID: " + insuranceObject.getLngInsuranceId());
        System.out.println("Name: " + insuranceObject.getInsuranceName());
      }
      
          session.close();
    }catch(Exception e){
      System.out.println(e.getMessage());
      e.printStackTrace();
    }
    
  }
}

Following query is used to calculate the average of  invested amount:

/*Hibernate Native Query Average Examle*/

String sql ="selectstddev(ins.invested_amount) as stdErr, "+ " avg(ins.invested_amount) as mean"+ " from insurance ins";

The following code:

Query query = session.createSQLQuery(sql).addScalar("stdErr",Hibernate.DOUBLE).
addScalar("mean",Hibernate.DOUBLE);

Creates a new instance of SQLQuery for the given SQL query string and theentities returned by the query are detached. 

To return all the entities from database we have used the following query:

/* Example to show Native query to select all the objects from database */
/* Selecting all the objects from insurance table */
List insurance = session.createSQLQuery("select {ins.*} from insuranceins")
.addEntity("ins", Insurance.class)
.list();
    for (Iterator it = insurance.iterator(); it.hasNext();) {
    Insurance insuranceObject = (Insurance) it.next();
    System.out.println("ID: " + insuranceObject.getLngInsuranceId());
   System.out.println("Name: " + insuranceObject.getInsuranceName());
}

When you run the program through it should display the following result:

log4j:WARN No appenderscould be found for logger (org.hibernate.cfg.Environment).

log4j:WARN Please initialize the log4j system properly.

Hibernate: select stddev(ins.invested_amount) as stdErr,avg(ins.invested_amount) as mean from insurance ins

mean amount: 592.1584

stdErr amount: 923.5714

Hibernate: select ins.ID as ID0_, ins.insurance_name asinsurance2_2_0_, ins.invested_amount as invested3_2_0_,ins.investement_date as investem4_2_0_ from insurance ins

ID: 1

Name: Car Insurance

ID: 2

Name: Life Insurance

ID: 3

Name: Life Insurance

ID: 4

Name: Car Insurance

......

.......

In this example you learned how to use Native Query with Hibernate.