Hibernate Count Query

In this section we will show you, how to use the Count Query. Hibernate supports multiple aggregate functions. when they are used in HQL queries, they return an aggregate value (such as sum, average, and count) calculated from property values of all objects satisfying other query criteria.

"SELECT COUNT(*) FROM Student student"
 
Student.java
package com.sdnext.hibernate.tutorial.dto;

import java.io.Serializable;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Table;

@Entity
@Table(name="STUDENT")
public class Student implements Serializable 
{

 /**
  * serialVersionUID
  */
 private static final long serialVersionUID = 8633415090390966715L;
 @Id
 @Column(name="ID")
 @GeneratedValue(strategy=GenerationType.AUTO)
 private int id;
 @Column(name="STUDENT_NAME")
 private String studentName;
 @Column(name="ROLL_NUMBER")
 private int rollNumber;
 @Column(name="COURSE")
 private String course;
 public int getId() {
  return id;
 }
 public void setId(int id) {
  this.id = id;
 }
 public String getStudentName() {
  return studentName;
 }
 public void setStudentName(String studentName) {
  this.studentName = studentName;
 }
 public int getRollNumber() {
  return rollNumber;
 }
 public void setRollNumber(int rollNumber) {
  this.rollNumber = rollNumber;
 }
 public String getCourse() {
  return course;
 }
 public void setCourse(String course) {
  this.course = course;
 }
}
hibernate.cfg.xml
<!--?xml version="1.0" encoding="UTF-8"?-->

<!--?DOCTYPE hibernate-configuration PUBLIC
        "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
        "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd"-->
<hibernate-configuration> 
 <session-factory> 
  <!-- Database connection settings -->
   <property name="connection.driver_class">com.mysql.jdbc.Driver</property> 
   <property name="connection.url">jdbc:mysql://localhost:3306/hibernateDB2</property> 
   <property name="connection.username">root</property> 
   <property name="connection.password">root</property> 

  <!-- JDBC connection pool (use the built-in) -->
   <property name="connection.pool_size">1</property> 

  <!-- SQL dialect -->
   <property name="dialect">org.hibernate.dialect.MySQLDialect</property> 

  <!-- Enable Hibernate's automatic session context management -->
    <property name="current_session_context_class">thread</property> 
  
  <!-- Disable the second-level cache -->
   <property name="cache.provider_class">org.hibernate.cache.NoCacheProvider</property> 

  <!-- Echo all executed SQL to stdout -->
   <property name="show_sql">true</property> 
  
  <!-- Drop and re-create the database schema on startup -->
   <property name="hbm2ddl.auto">update</property> 
      
   <mapping class="com.sdnext.hibernate.tutorial.dto.Student">
      
  </mapping></session-factory> 
 </hibernate-configuration>
HibernateTestDemo.java
package com.sdnext.hibernate.tutorial;

import java.util.Iterator;

import org.hibernate.Query;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.AnnotationConfiguration;

public class HibernateTestDemo {
 /**
  * @param args
  */
 public static void main(String[] args) 
 {
  SessionFactory sessionFactory = new AnnotationConfiguration().configure().buildSessionFactory();
  Session session = sessionFactory.openSession();
  session.beginTransaction();
  
  String SQL_QUERY = "SELECT COUNT(*) FROM Student student";
  Query query = session.createQuery(SQL_QUERY);
    
  for(Iterator it=query.iterate();it.hasNext();)
  {
   long row = (Long) it.next();
   System.out.print("Count: " + row);
  }
  session.getTransaction().commit();
  session.close();
 }
}
Output:
log4j:WARN No appenders could be found for logger (org.hibernate.cfg.annotations.Version).
log4j:WARN Please initialize the log4j system properly.
Hibernate: select count(*) as col_0_0_ from STUDENT student0_
Count: 8

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