hibernate
Count total records in Hibernate with Projections
With this example we are going to demonstrate how to count total records in Hibernate using the Projections Class. In short, to count the total records in Hibernate using Projections we have set the example below:
Employee
class is the class whose objects will be inserted to the database.- In
CountTotalRecordsInHibernateWithProjections
we use the Hibernate API to make the interface with the database. - We create a new
Configuration
, that allows the application to specify properties and mapping documents to be used when creating aSessionFactory
. Usually an application will create a singleConfiguration
, build a single instance ofSessionFactory
and then instantiateSessions
in threads servicing client requests. Usingconfigure()
API method we use the mappings and properties specified in an application resource namedhibernate.cfg.xml
. Then, withbuildSessionFactory()
we instantiate a newSessionFactory
, using the properties and mappings in this configuration. - Use the
getCurrentSession()
API method to obtain the current session. - Use the
beginTransaction()
API method to begin a unit of work and return the associatedTransaction
object. If a new underlying transaction is required, begin the transaction. Otherwise continue the new work in the context of the existing underlying transaction. - Create new
Employee
objects and usesave(Object object)
API method ofSession
to persist the given transient instances to the database. - Use
getTransaction()
API method ofSession
andcommit()
API method of Transaction to commit theTransaction
. - Use the
beginTransaction()
API method again. Now create a newCriteria
, using thecreateCriteria(Class persistentClass)
API method ofSession
for the givenEmployee
class. - Use
setProjection(Projection projection)
to specify that the query results will be a projection (scalar in nature). - Use
rowCount()
API method ofProjections
to get the query row count. - Use the
list()
API method of Criteria to get the results, after having applied the constraints. Use again
getTransaction()
API method of Session and commit()
API method of Transaction to commit the Transaction
.In the code snippets that follow, you can see the Employee
class and the CountTotalRecordsInHibernateWithProjections
Class that applies all above steps. You can also take a look at the hibernate.cfg.xml
file, that holds all configuration for Hibernate, such as JDBC connection settings, and employee.hbm.xml
file that holds the mapping configuration between the Employee
class and the Employee table.
package com.javacodegeeks.snippets.enterprise; import java.util.Date; import java.util.List; import org.hibernate.Criteria; import org.hibernate.HibernateException; import org.hibernate.Session; import org.hibernate.SessionFactory; import org.hibernate.cfg.Configuration; import org.hibernate.criterion.Projections; public class CountTotalRecordsInHibernateWithProjections { @SuppressWarnings("unchecked") public static void main(String[] args) { SessionFactory sessionFactory = new Configuration().configure().buildSessionFactory(); Session session = sessionFactory.getCurrentSession(); try { session.beginTransaction(); for (int i = 0; i < 100; i++) { Employee employee = new Employee(); employee.setName("employe_"+i); employee.setSurname("surname_"+i); employee.setTitle("Engineer_"+i); employee.setCreated(new Date()); session.save(employee); } session.getTransaction().commit(); } catch (HibernateException e) { e.printStackTrace(); session.getTransaction().rollback(); } session = sessionFactory.getCurrentSession(); try { session.beginTransaction(); Criteria criteria = session.createCriteria(Employee.class); criteria.setProjection(Projections.rowCount()); List employees = criteria.list(); if (employees!=null) { Integer rowCount = (Integer) employees.get(0); System.out.println("Total Results:" + rowCount); } session.getTransaction().commit(); } catch (HibernateException e) { e.printStackTrace(); session.getTransaction().rollback(); } } }
package com.javacodegeeks.snippets.enterprise; import java.util.Date; public class Employee { private Long id; private String name; private String surname; private String title; private Date created; public Long getId() { return id; } public void setId(Long id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } public String getSurname() { return surname; } public void setSurname(String surname) { this.surname = surname; } public String getTitle() { return title; } public void setTitle(String title) { this.title = title; } public Date getCreated() { return created; } public void setCreated(Date created) { this.created = created; } }
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> <!-- JDBC connection settings --> <property name="connection.driver_class">com.mysql.jdbc.Driver</property> <property name="connection.url">jdbc:mysql://localhost/companydb</property> <property name="connection.username">jcg</property> <property name="connection.password">jcg</property> <!-- JDBC connection pool, use Hibernate internal connection pool --> <property name="connection.pool_size">5</property> <!-- Defines the SQL dialect used in Hiberante's application --> <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> <!-- Display and format all executed SQL to stdout --> <property name="show_sql">true</property> <property name="format_sql">true</property> <!-- Drop and re-create the database schema on startup --> <property name="hbm2ddl.auto">update</property> <!-- Mapping to hibernate mapping files --> <mapping resource="Employee.hbm.xml" /> </session-factory> </hibernate-configuration>
Employee.hbm.xml
<?xml version="1.0"?> <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"> <hibernate-mapping> <class name="com.javacodegeeks.snippets.enterprise.Employee" table="employee"> <id name="id" column="id"> <generator class="native"/> </id> <property name="name" not-null="true" length="50" /> <property name="surname" not-null="true" length="50" /> <property name="title" length="50" /> <property name="created" type="timestamp" /> </class> </hibernate-mapping>
Output:
Total Results:100
This was an example of how to count total records in Hibernate using the Projections
API.