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.tutoraspire.jpa.inheritence package and specify all the required variables and annotations.

Employee.java

  package com.tutoraspire.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.tutoraspire.jpa.inheritence package.

ActiveEmployee.java

  package com.tutoraspire.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.tutoraspire.jpa.inheritence package.

RetiredEmployee.java

  package com.tutoraspire.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.tutoraspire.jpa.inheritence.ActiveEmployee</class>        <class>com.tutoraspire.jpa.inheritence.RetiredEmployee</class>        <class>com.tutoraspire.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.tutoraspire.jpa.persistence package. This class is used to initialize an object and persist it.

EmployeePersistence.java

  package com.tutoraspire.jpa.persistence;    import javax.persistence.*;  import com.tutoraspire.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

Next Topic#

JPA Table-per-class Strategy

JPA Table-per-class Strategy

Table-per-class Example

Access modifiers in java

Best File Manager for Kali Linux

You may also like