JPA Table-per-class Strategy

In table-per-class strategy, for each sub entity class a separate table is generated. Unlike joined strategy, no separate table is generated for parent entity class in table-per-class strategy.

The following syntax represents the table-per-class strategy: -

Table-per-class Example

In this example, we will categorize employees into active employees and retired employees.

Thus, the subclass ActiveEmployees and RetiredEmployees inherits the e_id and e_name fields of parent class Employee.

Now, follow the below steps to create JPA project,

Create a root entity class Employee.java under the com.javatpoint.jpa.inheritence package and specify all the required variables and annotations.

Employee.java

package com.javatpoint.jpa.inheritence;

import java.io.Serializable;

import javax.persistence.*;

@Entity
@Table(name="employee_details")
@Inheritance(strategy=InheritanceType.TABLE_PER_CLASS)
public class Employee implements Serializable {
	
@Id	
private int e_id;
private String e_name;

public Employee(int e_id, String e_name) {
	super();
	this.e_id = e_id;
	this.e_name = e_name;
}

public Employee() {
	super();
	
}

public int getE_id() {
	return e_id;
}

public void setE_id(int e_id) {
	this.e_id = e_id;
}

public String getE_name() {
	return e_name;
}

public void setE_name(String e_name) {
	this.e_name = e_name;
}

}

Create an entity class ActiveEmployee.java (subclass of Employee.java) under com.javatpoint.jpa.inheritence package.

ActiveEmployee.java

package com.javatpoint.jpa.inheritence;
import javax.persistence.*;

@Entity
public class ActiveEmployee extends Employee {

	private int e_salary;
	private int e_experience;
	public ActiveEmployee(int e_id, String e_name, int e_salary, int e_experience) {
		super(e_id, e_name);
		this.e_salary = e_salary;
		this.e_experience = e_experience;
	}
	public ActiveEmployee() {
		super();
		
	}
	public int getE_salary() {
		return e_salary;
	}
	public void setE_salary(int e_salary) {
		this.e_salary = e_salary;
	}
	public int getE_experience() {
		return e_experience;
	}
	public void setE_experience(int e_experience) {
		this.e_experience = e_experience;
	}
	
	
	
}

Create another entity class RetiredEmployee.java (subclass of Employee.java) under com.javatpoint.jpa.inheritence package.

RetiredEmployee.java

package com.javatpoint.jpa.inheritence;

import javax.persistence.*;
@Entity
public class RetiredEmployee extends Employee {

	private int e_pension;
	
	public RetiredEmployee(int e_id, String e_name, int e_pension) {
		super(e_id, e_name);
		this.e_pension = e_pension;
	}

	public RetiredEmployee() {
		super();
	
	}

	

	public int getE_pension() {
		return e_pension;
	}

	public void setE_pension(int e_pension) {
		this.e_pension = e_pension;
	}

	

	
}

Now, map the entity class and other databases confiuguration in Persistence.xml file.

Persistence.xml

<persistence>
<persistence-unit name="Employee_details">
   
      <class>com.javatpoint.jpa.inheritence.ActiveEmployee</class>
      <class>com.javatpoint.jpa.inheritence.RetiredEmployee</class>
      <class>com.javatpoint.jpa.inheritence.Employee</class>

      
     <properties>
      <property name="javax.persistence.jdbc.driver" value="com.mysql.jdbc.Driver"/>
         <property name="javax.persistence.jdbc.url" value="jdbc:mysql://localhost:3306/employee"/>
         <property name="javax.persistence.jdbc.user" value="root"/>
         <property name="javax.persistence.jdbc.password" value=""/>
         <property name="eclipselink.logging.level" value="SEVERE"/>
         <property name="eclipselink.ddl-generation" value="create-or-extend-tables"/>
      </properties>
      </persistence-unit>
      </persistence>

Create a persistence class EmployeePersistence.java under com.javatpoint.jpa.persistence package. This class is used to initialize an object and persist it.

EmployeePersistence.java

package com.javatpoint.jpa.persistence;

import javax.persistence.*;
import com.javatpoint.jpa.inheritence.*;

public class EmployeePersistence {
	
	public static void main(String[] args) {
		
	EntityManagerFactory emf=Persistence.createEntityManagerFactory("Employee_details");
	EntityManager em=emf.createEntityManager();
	
	em.getTransaction().begin();
	
ActiveEmployee ae1=new ActiveEmployee(101,"Karun",10000,5);
ActiveEmployee ae2=new ActiveEmployee(102,"Rishab",12000,7);

RetiredEmployee re1=new RetiredEmployee(103,"Ramesh",5000);
RetiredEmployee re2=new RetiredEmployee(104,"Raj",4000);

	em.persist(ae1);
	em.persist(ae2);
	
	em.persist(re1);
	em.persist(re2);
	
	em.getTransaction().commit();
	
	em.close();
	emf.close();
	
}}

Output:

After the execution of the program, two tables are generated in MySQL workbench.

Now, fetch data from each table separately to generate the output.

Select * from active_employee

Select * from retired_employee

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