HQL : NamedQuery : Named Queries

Named queries allow you to write queries at entity level. If you are going to write same query again and again, then you can replace it with named queries.

package myFirstHibernate;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.NamedQuery;


@Entity(name="employee_details")
@NamedQuery(name="getByID", query="from employee_details where id = ?")
public class Employee {
  @Id @GeneratedValue
  private int id;
  private String firstName;
  private String lastName;
  
  public int getId() {
    return id;
  }
  
  public void setId(int id) {
    this.id = id;
  }
  
  public String getFirstName() {
    return firstName;
  }
  
  public void setFirstName(String firstName) {
    this.firstName = firstName;
  }
  
  public String getLastName() {
    return lastName;
  }
  
  public void setLastName(String lastName) {
    this.lastName = lastName;
  }
  
}

hibernate.cfg.xml

<?xml version='1.0' encoding='utf-8'?>
<!DOCTYPE hibernate-configuration PUBLIC
        "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
        "http://www.hibernate.org/dtd/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/sample</property>
    <property name="connection.username">root</property>
    <property name="connection.password">tiger</property>
    
    <!-- Enable the logging of all the generated SQL statements to the console -->
    <property name="show_sql">true</property>
    
    <!-- Format the generated SQL statement to make it more readable, -->
    <property name="format_sql">false</property>
    
    <!-- Hibernate will put comments inside all generated SQL statements to hint what’s the generated SQL trying to do -->
    <property name="use_sql_comments">false</property>
    
    <!-- This property makes Hibernate generate the appropriate SQL for the chosen database. -->
    <property name="dialect">org.hibernate.dialect.MySQLDialect</property>
    
    <!-- Drop and re-create the database schema on startup -->
    <property name="hbm2ddl.auto">create</property>
    
    <!-- mappings for annotated classes -->
    <mapping class="myFirstHibernate.Employee" />
    
  </session-factory>
  
</hibernate-configuration>

package myFirstHibernate;

import java.util.List;
import java.util.Iterator;
import org.hibernate.Query;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.boot.registry.StandardServiceRegistryBuilder;
import org.hibernate.cfg.Configuration;

public class TestEmployee {
  
  /* Step 1: Create session factory */
  private static SessionFactory getSessionFactory() {
    Configuration configuration = new Configuration().configure();
    StandardServiceRegistryBuilder builder = new StandardServiceRegistryBuilder().
    applySettings(configuration.getProperties());
    SessionFactory factory = configuration.buildSessionFactory(builder.build());
        return factory;
    }
  
  public static void main(String args[])throws Exception{
    
    Employee emp1 = new Employee();
    Employee emp2 = new Employee();
    Employee emp3 = new Employee();
    Employee emp4 = new Employee();
    Employee emp5 = new Employee();
    Employee emp6 = new Employee();
    Employee emp7 = new Employee();
    Employee emp8 = new Employee();
    
    emp1.setFirstName("Hari Krishna");
    emp1.setLastName("Gurram");
    
    emp2.setFirstName("Shreyas");
    emp2.setLastName("Desai");
    
    emp3.setFirstName("Piyush");
    emp3.setLastName("Rai");
    
    emp4.setFirstName("Rama Krishna");
    emp4.setLastName("Gurram");
    
    emp5.setFirstName("Sailaja");
    emp5.setLastName("Navakotla");
    
    emp6.setFirstName("Keerthi");
    emp6.setLastName("Parush");
    
    emp7.setFirstName("Gopi");
    emp7.setLastName("Battu");
    
    emp8.setFirstName("Jaideep");
    emp8.setLastName("Gera");
    
    SessionFactory sessionFactory = getSessionFactory();
    Session session = sessionFactory.openSession();
    session.beginTransaction();
    
    /* Saving objects to database */
    session.save(emp1);
    session.save(emp2);
    session.save(emp3);
    session.save(emp4);
    session.save(emp5);
    session.save(emp6);
    session.save(emp7);
    session.save(emp8);
  
    String empId = "4";
    
    Query query = session.getNamedQuery("getByID");
    query.setString(0, empId);
    
    List<Employee> list =  (List<Employee>)query.list();
    
    for(Employee emp : list)
      System.out.println(emp.getId() + " " + emp.getFirstName() + " " + emp.getLastName());
        
    session.getTransaction().commit();
    session.close(); 

    
  }
}

Run TestEmployee class, you will get output like below.

Hibernate: drop table if exists employee_details
Hibernate: create table employee_details (id integer not null auto_increment, firstName varchar(255), lastName varchar(255), primary key (id))
Dec 23, 2014 11:38:33 AM org.hibernate.tool.hbm2ddl.SchemaExport execute
INFO: HHH000230: Schema export complete
Dec 23, 2014 11:38:33 AM org.hibernate.hql.internal.ast.HqlSqlWalker generatePositionalParameter
WARN: [DEPRECATION] Encountered positional parameter near line 1, column 43.  Positional parameter are considered deprecated; use named parameters or JPA-style positional parameters instead.
Hibernate: insert into employee_details (firstName, lastName) values (?, ?)
Hibernate: insert into employee_details (firstName, lastName) values (?, ?)
Hibernate: insert into employee_details (firstName, lastName) values (?, ?)
Hibernate: insert into employee_details (firstName, lastName) values (?, ?)
Hibernate: insert into employee_details (firstName, lastName) values (?, ?)
Hibernate: insert into employee_details (firstName, lastName) values (?, ?)
Hibernate: insert into employee_details (firstName, lastName) values (?, ?)
Hibernate: insert into employee_details (firstName, lastName) values (?, ?)
Hibernate: select employee0_.id as id1_0_, employee0_.firstName as firstNam2_0_, employee0_.lastName as lastName3_0_ from employee_details employee0_ where employee0_.id=?
4 Rama Krishna Gurram

@Entity(name="employee_details")

@NamedQuery(name="getByID", query="from employee_details where id = ?")

public class Employee {

}

As you observe, I create a named query “getById”. It takes id as parameter and gets you the employee with specific id.

In TestEmployee.java class

I am accessing and setting the parameter for named query like below.

Query query = session.getNamedQuery("getByID");

query.setString(0, empId);

You can write any number of named queries for an entity. I will explain how to write more than one named query in next post.

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