Hibernate

HQL is an object-oriented query language, similar to SQL, but instead of operating on tables and columns, HQL works with persistent objects and their properties. It is a superset of the JPQL, the Java Persistence Query Language; a JPQL query is a valid HQL query, but not all HQL queries are valid JPQL queries. HQL is a language with its own syntax and grammar. It is written as strings, like ?from Product p?. your HQL queries are translated by Hibernate into conventional SQL queries; Hibernate also provides an API that allows you to directly issue SQL queries as well.


CREATE TABLE `Employee` (
  `emp_id` int(11) unsigned NOT NULL AUTO_INCREMENT,
  `emp_name` varchar(20) NOT NULL,
  `emp_salary` double(10,0) NOT NULL DEFAULT '0',
  PRIMARY KEY (`emp_id`)
) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8;
  
CREATE TABLE `Address` (
  `emp_id` int(11) unsigned NOT NULL,
  `address_line1` varchar(50) NOT NULL DEFAULT '',
  `zipcode` varchar(10) DEFAULT NULL,
  `city` varchar(20) DEFAULT NULL,
  PRIMARY KEY (`emp_id`),
  CONSTRAINT `emp_fk_1` FOREIGN KEY (`emp_id`) REFERENCES `Employee` (`emp_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
 
INSERT INTO `Employee` (`emp_id`, `emp_name`, `emp_salary`)
VALUES
    (1, 'Pankaj', 100),
    (2, 'David', 200),
    (3, 'Lisa', 300),
    (4, 'Jack', 400);
 
 
INSERT INTO `Address` (`emp_id`, `address_line1`, `zipcode`, `city`)
VALUES
    (1, 'Albany Dr', '95129', 'San Jose'),
    (2, 'Arques Ave', '95051', 'Santa Clara'),
    (3, 'BTM 1st Stage', '560100', 'Bangalore'),
    (4, 'City Centre', '100100', 'New Delhi');
     
commit;

pom.xml


<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>
  <groupId>com.journaldev.hibernate</groupId>
  <artifactId>HQLExample</artifactId>
  <version>0.0.1-SNAPSHOT</version>
  <dependencies>
    <dependency>
        <groupId>org.hibernate</groupId>
        <artifactId>hibernate-core</artifactId>
        <version>4.3.5.Final</version>
    </dependency>
    <dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
        <version>5.0.5</version>
    </dependency>
  </dependencies>
</project>

hibernate.cfg.xml


<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-configuration PUBLIC
        "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
        "http://hibernate.org/dtd/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
    <session-factory>
        <property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
        <property name="hibernate.connection.password">pankaj123</property>
        <property name="hibernate.connection.url">jdbc:mysql://localhost/TestDB</property>
        <property name="hibernate.connection.username">pankaj</property>
        <property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>
         
        <property name="hibernate.current_session_context_class">thread</property>
        <property name="hibernate.show_sql">true</property>
         
        <mapping class="com.journaldev.hibernate.model.Employee"/>
        <mapping class="com.journaldev.hibernate.model.Address"/>
    </session-factory>
</hibernate-configuration>

HibernateUtil.java


import org.hibernate.SessionFactory;
import org.hibernate.boot.registry.StandardServiceRegistryBuilder;
import org.hibernate.cfg.Configuration;
import org.hibernate.service.ServiceRegistry;
 
public class HibernateUtil {
 
    private static SessionFactory sessionFactory;
     
    private static SessionFactory buildSessionFactory() {
        try {
            // Create the SessionFactory from hibernate.cfg.xml
            Configuration configuration = new Configuration();
            configuration.configure("hibernate.cfg.xml");
            System.out.println("Hibernate Configuration loaded");
             
            ServiceRegistry serviceRegistry = new StandardServiceRegistryBuilder().applySettings(configuration.getProperties()).build();
            System.out.println("Hibernate serviceRegistry created");
             
            SessionFactory sessionFactory = configuration.buildSessionFactory(serviceRegistry);
             
            return sessionFactory;
        }
        catch (Throwable ex) {
            System.err.println("Initial SessionFactory creation failed." + ex);
            ex.printStackTrace();
            throw new ExceptionInInitializerError(ex);
        }
    }
     
    public static SessionFactory getSessionFactory() {
        if(sessionFactory == null) sessionFactory = buildSessionFactory();
        return sessionFactory;
    }
}

Employee.java


import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.OneToOne;
import javax.persistence.Table;
 
import org.hibernate.annotations.Cascade;
 
@Entity
@Table(name = "EMPLOYEE")
public class Employee {
 
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "emp_id")
    private long id;
 
    @Column(name = "emp_name")
    private String name;
 
    @Column(name = "emp_salary")
    private double salary;
 
    @OneToOne(mappedBy = "employee")
    @Cascade(value = org.hibernate.annotations.CascadeType.ALL)
    private Address address;
 
    public long getId() {
        return id;
    }
 
    public void setId(long id) {
        this.id = id;
    }
 
    public Address getAddress() {
        return address;
    }
 
    public void setAddress(Address address) {
        this.address = address;
    }
 
    public String getName() {
        return name;
    }
 
    public void setName(String name) {
        this.name = name;
    }
 
    public double getSalary() {
        return salary;
    }
 
    public void setSalary(double salary) {
        this.salary = salary;
    }
 
}

Address.java


import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.OneToOne;
import javax.persistence.PrimaryKeyJoinColumn;
import javax.persistence.Table;
 
import org.hibernate.annotations.GenericGenerator;
import org.hibernate.annotations.Parameter;
 
@Entity
@Table(name = "ADDRESS")
public class Address {
 
    @Id
    @Column(name = "emp_id", unique = true, nullable = false)
    @GeneratedValue(generator = "gen")
    @GenericGenerator(name = "gen", strategy = "foreign", 
                parameters = { @Parameter(name = "property", value = "employee") })
    private long id;
 
    @Column(name = "address_line1")
    private String addressLine1;
 
    @Column(name = "zipcode")
    private String zipcode;
 
    @Column(name = "city")
    private String city;
 
    @OneToOne
    @PrimaryKeyJoinColumn
    private Employee employee;
 
    public long getId() {
        return id;
    }
 
    public void setId(long id) {
        this.id = id;
    }
 
    public String getAddressLine1() {
        return addressLine1;
    }
 
    public void setAddressLine1(String addressLine1) {
        this.addressLine1 = addressLine1;
    }
 
    public String getZipcode() {
        return zipcode;
    }
 
    public void setZipcode(String zipcode) {
        this.zipcode = zipcode;
    }
 
    public String getCity() {
        return city;
    }
 
    public void setCity(String city) {
        this.city = city;
    }
 
    public Employee getEmployee() {
        return employee;
    }
 
    public void setEmployee(Employee employee) {
        this.employee = employee;
    }
 
}

HQLExamples.java


import java.util.Arrays;
import java.util.List;
 
import org.hibernate.Query;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
 
import com.journaldev.hibernate.model.Employee;
import com.journaldev.hibernate.util.HibernateUtil;
 
public class HQLExamples {
 
    @SuppressWarnings("unchecked")
    public static void main(String[] args) {
         
        //Prep work
        SessionFactory sessionFactory = HibernateUtil.getSessionFactory();
        Session session = sessionFactory.getCurrentSession();
         
        //Get All Employees
        Transaction tx = session.beginTransaction();
        Query query = session.createQuery("from Employee");
        List<Employee> empList = query.list();
        for(Employee emp : empList){
            System.out.println("List of Employees::"+emp.getId()+","+emp.getAddress().getCity());
        }
         
        //Get Employee with id
        query = session.createQuery("from Employee where id= :id");
        query.setLong("id", 3);
        Employee emp = (Employee) query.uniqueResult();
        System.out.println("Employee Name="+emp.getName()+", City="+emp.getAddress().getCity());
         
        //pagination example
        query = session.createQuery("from Employee");
        query.setFirstResult(0); //starts with 0
        query.setFetchSize(2);
        empList = query.list();
        for(Employee emp4 : empList){
            System.out.println("Paginated Employees::"+emp4.getId()+","+emp4.getAddress().getCity());
        }
         
        //Update Employee
        query = session.createQuery("update Employee set name= :name where id= :id");
        query.setParameter("name", "Pankaj Kumar");
        query.setLong("id", 1);
        int result = query.executeUpdate();
        System.out.println("Employee Update Status="+result);
 
        //Delete Employee, we need to take care of foreign key constraints too
        query = session.createQuery("delete from Address where id= :id");
        query.setLong("id", 4);
        result = query.executeUpdate();
        System.out.println("Address Delete Status="+result);
         
        query = session.createQuery("delete from Employee where id= :id");
        query.setLong("id", 4);
        result = query.executeUpdate();
        System.out.println("Employee Delete Status="+result);
         
        //Aggregate function examples
        query = session.createQuery("select sum(salary) from Employee");
        double sumSalary = (Double) query.uniqueResult();
        System.out.println("Sum of all Salaries= "+sumSalary);
         
        //join examples
        query = session.createQuery("select e.name, a.city from Employee e "
                + "INNER JOIN e.address a");
        List<Object[]> list = query.list();
        for(Object[] arr : list){
            System.out.println(Arrays.toString(arr));
        }
         
        //group by and like example
        query = session.createQuery("select e.name, sum(e.salary), count(e)"
                + " from Employee e where e.name like '%i%' group by e.name");
        List<Object[]> groupList = query.list();
        for(Object[] arr : groupList){
            System.out.println(Arrays.toString(arr));
        }
         
        //order by example
        query = session.createQuery("from Employee e order by e.id desc");
        empList = query.list();
        for(Employee emp3 : empList){
            System.out.println("ID Desc Order Employee::"+emp3.getId()+","+emp3.getAddress().getCity());
        }
         
        //rolling back to save the test data
        tx.rollback();
         
        //closing hibernate resources
        sessionFactory.close();
    }
 
}

After doing this kind of activity build and run the project. For doing this we need to go into the project node and right click on the project and select to the run project.

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