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Table per Class Hierarchy Using Annotation

Posted by on May 20, 2015 in Hibernate, Hibernate Annotation | 0 comments

Table per class hierarchy
 
In our previous tutorial we got introduced to Inheritance Mapping In Hibernate, In this article I will explain you about Table per Class Hierarchy Inheritance mapping. By this inheritance strategy, we can map the whole hierarchy in a single table. Here, an extra column otherwise known as discriminator column is created in the table to identify the class. In the table, for each record some columns will be empty; those columns for which the particular Java class does not have fields.
 
Inheritance
 
The above is the Hierarchy of classes involved. Here Employee is the super class for PermanentEmployee and ContractEmployee classes. Now Let us create Java classes for the above hierarchy to implement
 

Entity class

 
File: Employee.java

package entity;

import javax.persistence.Column;
import javax.persistence.DiscriminatorColumn;
import javax.persistence.DiscriminatorType;
import javax.persistence.DiscriminatorValue;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.Inheritance;
import javax.persistence.InheritanceType;
import javax.persistence.Table;

@Entity
@Table(name = "EMPLOYEE")
@Inheritance(strategy = InheritanceType.SINGLE_TABLE)
@DiscriminatorColumn(name = "DTYPE", discriminatorType = DiscriminatorType.STRING)
@DiscriminatorValue(value = "")
public class Employee {

	@Id
	@GeneratedValue
	@Column(name = "EMPID")
	private int empID;

	@Column(name = "EMP_NAME")
	private String empName;

	public int getEmpID() {
		return empID;
	}

	public String getEmpName() {
		return empName;
	}

	public void setEmpID(int empID) {
		this.empID = empID;
	}

	public void setEmpName(String empName) {
		this.empName = empName;
	}
}

 
In case of table per class hierarchy a discriminator column is added by the hibernate framework that specifies the type of the record. It is mainly used to identify which derived class object have been saved in the table (see Database screen shot for better understanding). To specify this, following annotation where used in Super class entity.
 
@Inheritance – Defines the inheritance strategy to be used for an entity class hierarchy. It is specified on the entity class that is the root of the entity class hierarchy.

@DiscriminatorColumn – Is used to define the discriminator column for the SINGLE_TABLE and JOINED inheritance mapping strategies. The strategy and the discriminator column are only specified in the root of an entity class hierarchy or sub hierarchy in which a different inheritance strategy is applied

If the @DiscriminatorColumn annotation is missing, and a discriminator column is required, the name of the discriminator column defaults to “DTYPE” and the discriminator type to DiscriminatorType.STRING.

@DiscriminatorValue – Is used to specify the value of the discriminator column for entities of the given type. The DiscriminatorValue annotation can only be specified on a concrete entity class. If the DiscriminatorValue annotation is not specified and a discriminator column is used, a provider-specific function will be used to generate a value representing the entity type. If the DiscriminatorType is STRING, the discriminator value default is the entity name.

The inheritance strategy and the discriminator column are only specified in the root of an entity class hierarchy or subhierarchy in which a different inheritance strategy is applied. The discriminator value, if not defaulted, should be specified for each entity class in the hierarchy.
 
File: PermanentEmployee.java

package entity;

import javax.persistence.Column;
import javax.persistence.DiscriminatorValue;
import javax.persistence.Entity;
import javax.persistence.Table;

@Entity
@Table(name = "EMPLOYEE")
@DiscriminatorValue("Permanent Employee")
public class PermanentEmployee extends Employee {

	@Column(name = "COMPANY_NAME")
	private String companyName;

	public String getCompanyName() {
		return companyName;
	}

	public void setCompanyName(String companyName) {
		this.companyName = companyName;
	}
}

 
PermanentEmployee class is child of Employee class. Thus while specifying the mappings, we used @DiscriminatorValue to specify discriminator value. In our case “Permanent Employee” will be persisted in discriminator column.
 
File: ContractEmployee.java

package entity;

import javax.persistence.Column;
import javax.persistence.DiscriminatorValue;
import javax.persistence.Entity;
import javax.persistence.Table;

@Entity
@Table(name = "EMPLOYEE")
@DiscriminatorValue("Contract Employee")
public class ContractEmployee extends Employee {

	@Column(name = "CONTRACTOR_NAME")
	private String contractorName;

	public String getContractorName() {
		return contractorName;
	}

	public void setContractorName(String contractorName) {
		this.contractorName = contractorName;
	}
}

 

Hibernate Configuration file

 

<hibernate-configuration>
<session-factory>
	<!-- Database connection settings -->
	<property name="hibernate.connection.driver_class">oracle.jdbc.driver.OracleDriver</property>
	<property name="hibernate.connection.username">system</property>
	<property name="hibernate.connection.password">admin</property>
	<property name="hibernate.connection.url">jdbc:oracle:thin:@xxx.x.x.x:1521:XE</property>

	<!-- SQL dialect -->
	<property name="hibernate.dialect">org.hibernate.dialect.Oracle10gDialect</property>

	<!-- Echo all executed SQL to sysout -->
	<property name="show_sql">true</property>

	<!-- Drop and re-create the database schema on startup -->
	<property name="hibernate.hbm2ddl.auto">create</property>
	<!-- Map Entity Class -->
       <mapping class="entity.Employee"></mapping>
       <mapping class="entity.PermanentEmployee"></mapping>
       <mapping class="entity.ContractEmployee"></mapping>

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

 
The hbm2ddl.auto property is defined for creating automatic table in the database.
 

Client program

 
Create the class that stores the persistent object in this class, we are simply storing the employee objects in the database.
 

package util;

import entity.ContractEmployee;
import entity.PermanentEmployee;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.boot.registry.StandardServiceRegistryBuilder;
import org.hibernate.cfg.Configuration;
import org.hibernate.service.ServiceRegistry;

public class HibernateUtil {

	public static void main(String[] args) {

		Configuration cf = new Configuration().configure("hibernate.cfg.xml");

		StandardServiceRegistryBuilder srb = new StandardServiceRegistryBuilder();
		srb.applySettings(cf.getProperties());
		ServiceRegistry sr = srb.build();
		SessionFactory sf = cf.buildSessionFactory(sr);

		Session session = sf.openSession();

		PermanentEmployee p1 = new PermanentEmployee();
		p1.setEmpID(1);
		p1.setEmpName("Ameer");
		p1.setCompanyName("CTS");

		PermanentEmployee p2 = new PermanentEmployee();
		p2.setEmpID(2);
		p2.setEmpName("Lourde");
		p2.setCompanyName("TCS");

		// create two objects of ContractEmployee
		ContractEmployee t1 = new ContractEmployee();
		t1.setEmpID(3);
		t1.setEmpName("Prabhu");
		t1.setContractorName("ABD Consultancy");

		ContractEmployee t2 = new ContractEmployee();
		t2.setEmpID(4);
		t2.setEmpName("Badru");
		t2.setContractorName("MN Consultancy");

		Transaction tx = session.beginTransaction();

		session.save(p1);
		session.save(p2);
		session.save(t1);
		session.save(t2);

		tx.commit();
		System.out.println("Object saved successfully !");
		session.close();
		sf.close();
	}
}

 

Eclipse Console

 
eclipse console

Database output

 
table-per-class

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Hibernate 4 Hello World example in Eclipse using Annotation

Posted by on May 20, 2015 in Hibernate | 1 comment

Hibernate Hello world
 
This is the 4th article on Hibernate in java application that describes on how to to save an object from java into the database using Hibernate 4(Hibernate 4 Insert Query). If you have not read my previous articles article on Generic Hibernate Application Requirements and Steps to be followed to use Hibernate in Java, I will recommend that you read that article first. You may want to look at Hibernate Installation/Setup on Eclipse IDE article if Hibernate is not installed already on your system.
 
As described earlier, the following files are the minimum requirement to shape an hibernate program..
 
StudentEntity.java (Entity class)
hibernate.cfg.xml (Xml configuration file)
HibernateUtil.java (Main class to access this configuration file and to write hibernate logic)
 

Project Structure

 
The final appearance of the application should be as follows:
 
HibernateHelloWorld
 

Entity class

 

package entity;

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

@Entity
@Table(name = "STUDENT")
public class StudentEntity {

	@Id
	@Column(name = "ID")
	private int id;
	
	@Column(name = "NAME")
	private String name;
	
	@Column(name = "DEPARTMENT")
	private String department;
	
	@Column(name = "COLLEGE")
	private String college;

// Create Getters and Setters
}

 
Note: I have explained about every annotations used in the above file in the article Generic Hibernate Application Requirements
 

Hibernate Configuration file

 
Create a new XML file and give this new configuration file the default name hibernate.cfg.xml and place it src directory of your project.
 
File: hibernate.cfg.xml

<!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="hibernate.connection.driver_class">
                  oracle.jdbc.driver.OracleDriver
        </property>
	<property name="hibernate.connection.username">system</property>
	<property name="hibernate.connection.password">admin</property>
	<property name="hibernate.connection.url">
                   jdbc:oracle:thin:@xxx.x.x.x:1521:XE
        </property>

	<!-- SQL dialect -->
	<property name="hibernate.dialect">org.hibernate.dialect.Oracle10gDialect</property>

	<!-- Echo all executed SQL to sysout -->
	<property name="show_sql">true</property>

	<!-- Drop and re-create the database schema on startup -->
	<property name="hibernate.hbm2ddl.auto">update</property>
	<!-- Map Entity Class -->
    <mapping class="entity.StudentEntity"></mapping>

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

 

Hibernate Utility

 
Create the Main class to run the example.
 

package util;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.boot.registry.StandardServiceRegistryBuilder;
import org.hibernate.cfg.Configuration;
import org.hibernate.service.ServiceRegistry;

import entity.StudentEntity;

public class HibernateUtil {

	public static void main(String[] args) {

        Configuration cf = new Configuration().configure("hibernate.cfg.xml");

        StandardServiceRegistryBuilder srb = new StandardServiceRegistryBuilder();
        srb.applySettings(cf.getProperties());
        ServiceRegistry sr = srb.build();
        SessionFactory sf = cf.buildSessionFactory(sr);

        Session session = sf.openSession();
    
        StudentEntity std = new StudentEntity();
		std.setId(24); // Primary Key
		std.setName("Jamil");
		std.setDepartment("ECE");
		std.setCollege("SKCET");

		Transaction tx = session.beginTransaction();
		session.save(std);
		tx.commit();
		System.out.println("Object saved successfully.....!!");
		session.close();
		sf.close();
	}
}

 
In the article Steps to be followed to use Hibernate in Java, I have explained the configuration/code used in above program in detail.
 
Now once our project is ready. Right click to project or right click to HibernateUtil.java and click Run As–>Java Application. Since I have set show_sql to true in hibernate.cfg.xml, so the hibernate create and insert quires will be displayed on eclipse console as below.
 
Hibernate Console
 
You will see the data stored in Student table in the database.
 
Hibernate Result
 
In my next article I have implemented Select Query in Hibernate
 

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Hibernate update query example

Posted by on Mar 20, 2015 in Hibernate, Hibernate Annotation | 0 comments

Update Query
 
In previous article we learnt to implement Hibernate delete Query example in Eclipse, in this article I will implement a program to update an object which is already persisted in the database.
 

Project Structure

 
HibernateHelloWorld
 

Entity class

 

package entity;

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

@Entity
@Table(name = "STUDENT")
public class StudentEntity {

	@Id
	@Column(name = "ID")
	private int id;
	
	@Column(name = "NAME")
	private String name;
	
	@Column(name = "DEPARTMENT")
	private String department;
	
	@Column(name = "COLLEGE")
	private String college;

// Create Getters and Setters
}

 
Note: I have explained about every annotations used in the above file in the article Generic Hibernate Application Requirements
 

Hibernate Configuration file

 
File: hibernate.cfg.xml

<hibernate-configuration>

<session-factory>
   <!-- Database connection settings -->
   <property name="hibernate.connection.driver_class">oracle.jdbc.driver.OracleDriver</property>
   <property name="hibernate.connection.username">system</property>
   <property name="hibernate.connection.password">admin</property>
   <property name="hibernate.connection.url">jdbc:oracle:thin:@127.0.0.1:1521:XE</property>

   <!-- SQL dialect -->
   <property name="hibernate.dialect">org.hibernate.dialect.Oracle10gDialect</property>

   <!-- Echo all executed SQL to sysout -->
   <property name="show_sql">true</property>

   <!-- Create/Update the database schema on startup -->
   <property name="hibernate.hbm2ddl.auto">update</property>
   <!-- Mapping file -->
   <mapping resource="Student.hbm.xml" />

</session-factory>

</hibernate-configuration>

 

Hibernate Utility

 

package util;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.boot.registry.StandardServiceRegistryBuilder;
import org.hibernate.cfg.Configuration;
import org.hibernate.service.ServiceRegistry;

import model.Student;

public class HibernateUtil {

	public static void main(String[] args) {

		Configuration cf = new Configuration().configure("hibernate.cfg.xml");

		StandardServiceRegistryBuilder srb = new StandardServiceRegistryBuilder();
		srb.applySettings(cf.getProperties());
		ServiceRegistry sr = srb.build();
		SessionFactory sf = cf.buildSessionFactory(sr);

		Session session = sf.openSession();

		Student std = (Student) session.load(Student.class, new Integer(2));
		Transaction tx = session.beginTransaction();

		// std.setId(3); // We Should not update "id"
		std.setName("Ameer");
		std.setCollege("PSG");
		tx.commit(); // Update method will be called implicitly.
		System.out.println("Object Updated successfully !");
		session.close();
		sf.close();
	}
}

 

Hibernate Cache

  • Whenever an object is loaded from database, hibernate stores the loaded object in cache memory which works in session scope.
  • Now if we do any modifications to the loaded object, then these modification are stored only in the object maintained by cache memory. Even if we modify the loaded object for multiple times then also the modifications will be stored only in the cached object.
  • But once we call transactions commit() method then hibernate will check whether there are any changes between the object present in the database and the object stored in the cache, now the if changes exists then hibernate will automatically call its update method internally and updates the student object in database.

 

Program Explanation

  • Line no 28: We should not update id, because we have loaded the object from the database only using this id member variable (See line no 25). So if we update this field, then hibernate will throws NonUniqueObjectException.
  • At line no 29, I have updated name property of student object.
  • Line no 31: So once commit() method is triggered from program, then hibernate will automatically call update method internally and updates the student object.

 

Data in DB before running the program

 
Hibernate DB
 

Run it – Eclipse Console

 
Hibernate Update
 

Data in DB after running the program

 
Update DB
 

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Hibernate Delete Query example

Posted by on Mar 16, 2015 in Hibernate, Hibernate Annotation | 0 comments

Hibernate Delete Query
 
In previous article we learnt to implement Hibernate Select Query example in Eclipse, In this article I will implement an example on delete the object from the database(Delete Query) using Hibernate.
 

Project Structure

 
HibernateHelloWorld
 

Entity class

 

package entity;

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

@Entity
@Table(name = "STUDENT")
public class StudentEntity {

	@Id
	@Column(name = "ID")
	private int id;
	
	@Column(name = "NAME")
	private String name;
	
	@Column(name = "DEPARTMENT")
	private String department;
	
	@Column(name = "COLLEGE")
	private String college;

// Create Getters and Setters
}

 
Note: I have explained about every annotations used in the above file in the article Generic Hibernate Application Requirements
 

Hibernate Configuration file

 
Create a new XML file and give this new configuration file the default name hibernate.cfg.xml and place it src directory of your project.
 
File: hibernate.cfg.xml

<!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="hibernate.connection.driver_class">
                  oracle.jdbc.driver.OracleDriver
        </property>
	<property name="hibernate.connection.username">system</property>
	<property name="hibernate.connection.password">admin</property>
	<property name="hibernate.connection.url">
                   jdbc:oracle:thin:@xxx.x.x.x:1521:XE
        </property>

	<!-- SQL dialect -->
	<property name="hibernate.dialect">org.hibernate.dialect.Oracle10gDialect</property>

	<!-- Echo all executed SQL to sysout -->
	<property name="show_sql">true</property>

	<!-- Drop and re-create the database schema on startup -->
	<property name="hibernate.hbm2ddl.auto">update</property>
	<!-- Map Entity Class -->
    <mapping class="entity.StudentEntity"></mapping>

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

 

Hibernate Utility

 

package util;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.boot.registry.StandardServiceRegistryBuilder;
import org.hibernate.cfg.Configuration;
import org.hibernate.service.ServiceRegistry;

import entity.StudentEntity;

public class HibernateUtil {

	public static void main(String[] args) {

		Configuration cf = new Configuration().configure("hibernate.cfg.xml");

		StandardServiceRegistryBuilder srb = new StandardServiceRegistryBuilder();
		srb.applySettings(cf.getProperties());
		ServiceRegistry sr = srb.build();
		SessionFactory sf = cf.buildSessionFactory(sr);

		Session session = sf.openSession();
		StudentEntity std = (StudentEntity) session.load(StudentEntity.class, new Integer(2));
		Transaction tx = session.beginTransaction();
		session.delete(std);
		tx.commit();
		System.out.println("Object Deleted successfully !");
		session.close();
		sf.close();
	}
}

 
In the above program we are deleting an object, which is already persisted (inserted) in the database; So in order to delete an persisted object, we need to load that object from the database and pass that object to the delete() method of Session interface, now hibernate delete that object whenever the transaction is committed.
 
In the article Steps to be followed to use Hibernate in Java, I have explained the configuration/code used in above program in detail.
 

Data in DB before running the program

 
Hibernate DB
 

Run it – Eclipse Console

 
Hibernate Delete
 

Data in DB after running the program

 
Delete after
 

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Generic Hibernate Application Requirements – Annotation

Posted by on Mar 15, 2015 in Hibernate | 0 comments

Hibernate Generic Requirment
 
The objective of this example is to understand the general requirement to be followed in creating any hibernate application in Java. You may want to look at Hibernate Installation/Setup on Eclipse IDE article if Hibernate is not installed already on your system.
 
In general any hibernate application, must have the following 3 files,
 
1) Configuration XML – This file will be used to store database connection information and schema level settings.
2) Entity Class – This class will be java POJO having hibernate annotations.
3) Java file to access this configuration file and write our logic
 
These files are the minimum requirement to run any hibernate application, in case of complex application we may require many Entity classes.
Note : Number of Entity classes = Number of Tables in database
 

Hibernate Configuration file

 
In this mapping file Hibernate gets to know about the type of database and its connection properties as well as about the Entity class.
 
File: hibernate.cfg.xml

<!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="hibernate.connection.driver_class">
                  oracle.jdbc.driver.OracleDriver
        </property>
	<property name="hibernate.connection.username">system</property>
	<property name="hibernate.connection.password">admin</property>
	<property name="hibernate.connection.url">
                   jdbc:oracle:thin:@xxx.x.x.x:1521:XE
        </property>

	<!-- SQL dialect -->
	<property name="hibernate.dialect">org.hibernate.dialect.Oracle10gDialect</property>

	<!-- Echo all executed SQL to sysout -->
	<property name="show_sql">true</property>

	<!-- Drop and re-create the database schema on startup -->
	<property name="hibernate.hbm2ddl.auto">update</property>
	<!-- Map Entity Class -->
    <mapping class="entity.StudentEntity"></mapping>

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

 

Entity class

 
The entity class is where the Hibernate mapping comes into play, this class tells Hibernate what table in the database it has to access, and what columns in that table it should use. For each member variable defined in Entity class you must create a getter and a setter.
 
File: StudentEntity.java
 

package entity;

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

@Entity
@Table(name = "STUDENT")
public class StudentEntity {

	@Id	
	@Column(name = "ID")
	private int id;
	
	@Column(name = "NAME")
	private String name;
	
	@Column(name = "DEPARTMENT")
	private String department;
	
	@Column(name = "COLLEGE")
	private String college;

// Create Getters and Setters
}

 
As shown above, the mapping file contains several annotations, listed below are its role:

  • @Entity annotation marks this class as an entity bean
  • @Table annotation allows you to specify the details of the table that will be used to persist the entity in the database.

    The @Table annotation provides four attributes, allowing you to override the name of the table, its catalogue, and its schema, and enforce unique constraints on columns in the table. For now we are using just table name which is STUDENT.

  • @Id Annotations:– In hibernate each entity bean should have a primary key, which you annotate on the class with the @Id annotation. The primary key can be a single field or a combination of multiple fields depending on your table structure.
  • @Column, The @Column annotation is used to specify the details of the column to which a field or property will be mapped. Here the name attribute in @Column permits the name of the column to be explicitly specified.

 
In our next article we shall learn about Generic Steps to be followed to use Hibernate in any Java application, going forward using this two articles we shall implement Hello World example of Hibernate 4 in Eclipse

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