Hibernate Introduction Part 3

Data query.

Well, Now we will see how to query all the records inserted into the database that we have done
in part 1 and part 2.

For all the future examples (including this), i am going use only JPA Annotations

let's start.

Step 1: Development environment

1. My sql server 5.0  Download
2. Hibernate 4.1.1 Download
3. JDBC Driver for Mysql ((mysql-connector-java-5.1.19.zip)) Download
4. Eclipse IDE

Unzip the hibernate buddle and you should have the following structure after you unzip
Documentation folder
lib Folder
Project folder
log text file
hibernate logo image
license text file


Step 2:

Open mysql and create the following table in any of the exisitng database or create new database.
Here is the script for our table


CREATE TABLE `patient`
 (
    `ID` INT(11) NOT NULL AUTO_INCREMENT,
    `FirstName` VARCHAR(100) DEFAULT NULL,
    `LastName` VARCHAR(100) DEFAULT NULL,
    `Email` VARCHAR(200) DEFAULT NULL,
     PRIMARY KEY  (`ID`)
 )  ENGINE=INNODB DEFAULT


Step 3: Eclipse Java project

1. Click File -> New -> Other -> Java Project

2. Say Example3 for Project Name and leave all other to default values.
   (Make sure, JRE has been configured).

3. Next we will add all dependencies in the example3. Now click Example3 project in the project
   explorer and right click -> Click New-> Folder. Say folder name as lib

   Now copy the following files into lib folder
   (Note : Eclipse project explorer accepts all copy and paste operation. For example, you can copy    

   file or folder in windows explorer and then you can come back to eclipse project explorer and paste

  it)

   All the files in Hibernate->Lib->required.
   All the files in Hibernate->Lib->jpa.
   All the files in Hibernate->Lib->envers
   mysql-connector-java-5.1.18-bin.jar


4. Now  setup the build path. In order to execute our example, all the above jar files should be in
   class build path

   Again, click on the Example1, right click, and select build Path->configure build path.
   Go to Libraries-> External jars,  browse lib folder you created earlier. Then add external jars by
   selecting all jar files that you copied to lib folder in one of previous step


Step 4: Creating Java beans

Now let us create the java bean for the patient where we want to store in the database.

Again, right click on Example1, Select New -> Class; Package Name : mypack and Class name

:patient Leave the all other to default values

Now type or copy the following


package mypack;

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

@Entity
@Table(name="patient")
public class patient {

private Integer id;
private String firstName;
private String lastName;

@Id
@GeneratedValue
@Column(name="ID")
public Integer getId() {
return id;
}

public void setId(Integer id) {
this.id = id;
}

@Column(name="firstname")
public String getFirstName() {
return firstName;
}

public void setFirstName(String firstName) {
this.firstName = firstName;
}

@Column(name="lastname")
public String getLastName() {
return lastName;
}

public void setLastName(String lastName) {
this.lastName = lastName;
}

}



Step 6 : Hibernate Configuration

Now we have the persistent class and its mapping information using Annotations in place.
Let’s configure Hibernate.



Right Click src->New->File. File Name as hibernate.hbm.xml
Paste following code there. Save it as hibernate.cfg.xml. Here you have to give the

username,password and database name according to your MySQL account.


<?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/sampledb</property>
 <property name="connection.username">root</property>
 <property name="connection.password">123</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 files -->
  <mapping resource="patient.hbm.xml" />

  </session-factory>
</hibernate-configuration>


Step 7: Create Test class to store the objects

To create new class right click on "mypack" package and select New --> Class and give Name as

Test.java and paste the following code in class file.



package mypack;

import java.util.List;

import org.hibernate.Query;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;
import org.hibernate.service.ServiceRegistry;
import org.hibernate.service.ServiceRegistryBuilder;
import org.hibernate.HibernateException;

public class Test {

private static SessionFactory factory;
private static ServiceRegistry serviceRegistry;

public static void main(String[] args) {
createRecords();

}

public static void createRecords() {

try {
Configuration configuration = new Configuration();
configuration.configure();
serviceRegistry = new ServiceRegistryBuilder().applySettings(
configuration.getProperties()).buildServiceRegistry();
factory = configuration.buildSessionFactory(serviceRegistry);
} catch (Throwable ex) {
System.err.println("Failed to create sessionFactory object." + ex);
throw new ExceptionInInitializerError(ex);
}
System.out.println("**Example : Hibernate 4 SessionFactory**");
System.out.println("----------------------------------------");

Session session = factory.openSession();
Transaction tx = null;
try {
tx = session.beginTransaction();
patient pt = new patient();
pt.setFirstName("John124");
pt.setLastName("Smith234");
session.saveOrUpdate(pt);
tx.commit();
} catch (HibernateException e) {
if (tx != null)
tx.rollback();
e.printStackTrace();
} finally {
session.close();
}
}

}


Now right click on test.java file and select Run as -> Java Application
If every thing configured correctly, then you will the see the following lines in the console at the
end

INFO: HHH000126: Indexes: [primary]
Apr 29, 2012 10:14:49 PM org.hibernate.tool.hbm2ddl.SchemaUpdate execute
INFO: HHH000232: Schema update complete
**Example : Hibernate 4 SessionFactory**
----------------------------------------
Hibernate: insert into PATIENT (FIRSTNAME, LASTNAME) values (?, ?)

Now go to database and check records are inserted into patient table.

Run again and again to insert more records by changing the last name and first name.
So that in the next step, we can see how we can retrieve the records.


Step 7: Get records and display in the console.

Small Intro on Hibernate Query Language

Hibernate uses a powerful query language (HQL) that is similar in appearance to SQL. Compared with SQL,

however, HQL is fully object-oriented and understands notions like inheritance, polymorphism and

association. Since it is an object-oriented equivalent of SQL, all of the functions of retrieval are

provided out-of-the-box in HQL. These functions can be classified into four categories:

1. Projection

2. Restriction

3. Aggregation

4. Grouping


Examples for Projection
"from patient"

The above will returns all of the instances of the patient.
This is equivalent to the following SQL : SELECT * FROM patient

Examples for Restriction
SELECT * FROM patient WHERE lastname='John';

Coming back to our example, let us get all the patients from the database and print the last name
in the console.

Modified Test.Java as follows

package mypack;

import java.util.List;

import org.hibernate.Query;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;
import org.hibernate.service.ServiceRegistry;
import org.hibernate.service.ServiceRegistryBuilder;
import org.hibernate.HibernateException;

public class Test {

private static SessionFactory factory;
private static ServiceRegistry serviceRegistry;

public static void main(String[] args) {
createRecords();
getAllRecords();

}

public static void createRecords() {

try {
Configuration configuration = new Configuration();
configuration.configure();
serviceRegistry = new ServiceRegistryBuilder().applySettings(
configuration.getProperties()).buildServiceRegistry();
factory = configuration.buildSessionFactory(serviceRegistry);
} catch (Throwable ex) {
System.err.println("Failed to create sessionFactory object." + ex);
throw new ExceptionInInitializerError(ex);
}
System.out.println("**Example : Hibernate 4 SessionFactory**");
System.out.println("----------------------------------------");

Session session = factory.openSession();
Transaction tx = null;
try {
tx = session.beginTransaction();
patient pt = new patient();
pt.setFirstName("John12");
pt.setLastName("Smith23");
session.saveOrUpdate(pt);
tx.commit();
} catch (HibernateException e) {
if (tx != null)
tx.rollback();
e.printStackTrace();
} finally {
session.close();
}
}

public static void getAllRecords() {

try {
Configuration configuration = new Configuration();
configuration.configure();
serviceRegistry = new ServiceRegistryBuilder().applySettings(
configuration.getProperties()).buildServiceRegistry();
factory = configuration.buildSessionFactory(serviceRegistry);
} catch (Throwable ex) {
System.err.println("Failed to create sessionFactory object." + ex);
throw new ExceptionInInitializerError(ex);
}
System.out.println("**Example : Hibernate  SessionFactory**");
System.out.println("----------------------------------------");

List allpatients;

Session session = factory.openSession();
Transaction tx = null;
try {
tx = session.beginTransaction();
Query q1 = session.createQuery("from patient");
allpatients = q1.list();
for (int i =0; i < allpatients.size(); i++)
{
patient pt = (patient) allpatients.get(i);
System.out.println(pt.getLastName());
}
tx.commit();
} catch (HibernateException e) {
if (tx != null)
tx.rollback();
e.printStackTrace();
} finally {
session.close();
}
}

}


Now right click on test.java file and select Run as -> Java Application. Last name will be
printed in the console.