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Hibernate Tips
- Anand Nerurkar
- Apr 30, 2024
- 2 min read
Updated: May 1, 2024
Inheritance Strategy
annotation approach
===
1.Table Per Hierarchy
Entire class hierarchy is mapped to single table. Extra coulmn like discriminator is added and value represent type of class it represent in hierarchy.
@Inheritance(strategy=InheritanceType.SINGLE_TABLE), @DiscriminatorColumn and @DiscriminatorValue annotations for mapping table per hierarchy strategy.
In case of table per hierarchy, only one table is required to map the inheritance hierarchy. Here, an extra column (also known as discriminator column) is created in the table to identify the class.
import javax.persistence.*;
@Entity
@Table(name = "employee101")
@Inheritance(strategy=InheritanceType.SINGLE_TABLE)
@DiscriminatorColumn(name="type",discriminatorType=DiscriminatorType.STRING)
@DiscriminatorValue(value="employee")
public class Employee {
@Id
@GeneratedValue(strategy=GenerationType.AUTO)
@Column(name = "id")
private int id;
@Column(name = "name")
private String name;
//setters and getters
}
File: Regular_Employee.java
import javax.persistence.*;
@Entity
@DiscriminatorValue("regularemployee")
public class Regular_Employee extends Employee{
@Column(name="salary")
private float salary;
@Column(name="bonus")
private int bonus;
//setters and getters
}
File: Contract_Employee.java
import javax.persistence.Column;
import javax.persistence.DiscriminatorValue;
import javax.persistence.Entity;
@Entity
@DiscriminatorValue("contractemployee")
public class Contract_Employee extends Employee{
@Column(name="pay_per_hour")
private float pay_per_hour;
@Column(name="contract_duration")
private String contract_duration;
//setters and getters
}
public class StoreTest {
public static void main(String args[])
{
StandardServiceRegistry ssr = new StandardServiceRegistryBuilder().configure("hibernate.cfg.xml").build();
Metadata meta = new MetadataSources(ssr).getMetadataBuilder().build();
SessionFactory factory=meta.getSessionFactoryBuilder().build();
Session session=factory.openSession();
Transaction t=session.beginTransaction();
Employee e1=new Employee();
e1.setName("Gaurav Chawla");
Regular_Employee e2=new Regular_Employee();
e2.setName("Vivek Kumar");
e2.setSalary(50000);
e2.setBonus(5);
Contract_Employee e3=new Contract_Employee();
e3.setName("Arjun Kumar");
e3.setPay_per_hour(1000);
e3.setContract_duration("15 hours");
session.persist(e1);
session.persist(e2);
session.persist(e3);
t.commit();
session.close();
System.out.println("success");
}
}
Output:
Download this inheritance mapping example (Developed using Eclipse IDE)
Table Per Concrete class
In case of table per concrete class, tables are created as per class. But duplicate column is added in subclass tables.
Here, we need to use @Inheritance(strategy = InheritanceType.TABLE_PER_CLASS) annotation in the parent class and @AttributeOverrides annotation in the subclasses.
@Inheritance(strategy = InheritanceType.TABLE_PER_CLASS) specifies that we are using table per concrete class strategy. It should be specified in the parent class only.
@AttributeOverrides defines that parent class attributes will be overriden in this class. In table structure, parent class table columns will be added in the subclass table.
import javax.persistence.*;
@Entity
@Table(name = "employee102")
@Inheritance(strategy = InheritanceType.TABLE_PER_CLASS)
public class Employee {
@Id
@GeneratedValue(strategy=GenerationType.AUTO)
@Column(name = "id")
private int id;
@Column(name = "name")
private String name;
//setters and getters
}
import javax.persistence.*;
@Entity
@Table(name="regularemployee102")
@AttributeOverrides({
@AttributeOverride(name="id", column=@Column(name="id")),
@AttributeOverride(name="name", column=@Column(name="name"))
})
public class Regular_Employee extends Employee{
@Column(name="salary")
private float salary;
@Column(name="bonus")
private int bonus;
//setters and getters
}
File: Contract_Employee.java
import javax.persistence.*;
@Entity
@Table(name="contractemployee102")
@AttributeOverrides({
@AttributeOverride(name="id", column=@Column(name="id")),
@AttributeOverride(name="name", column=@Column(name="name"))
})
public class Contract_Employee extends Employee{
@Column(name="pay_per_hour")
private float pay_per_hour;
@Column(name="contract_duration")
private String contract_duration;
public float getPay_per_hour() {
return pay_per_hour;
}
public void setPay_per_hour(float payPerHour) {
pay_per_hour = payPerHour;
}
public String getContract_duration() {
return contract_duration;
}
public void setContract_duration(String contractDuration) {
contract_duration = contractDuration;
}
}
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.boot.Metadata;
import org.hibernate.boot.MetadataSources;
import org.hibernate.boot.registry.StandardServiceRegistry;
import org.hibernate.boot.registry.StandardServiceRegistryBuilder;
public class StoreData {
public static void main(String[] args) {
StandardServiceRegistry ssr=new StandardServiceRegistryBuilder().configure("hibernate.cfg.xml").build();
Metadata meta=new MetadataSources(ssr).getMetadataBuilder().build();
SessionFactory factory=meta.getSessionFactoryBuilder().build();
Session session=factory.openSession();
Transaction t=session.beginTransaction();
Employee e1=new Employee();
e1.setName("Gaurav Chawla");
Regular_Employee e2=new Regular_Employee();
e2.setName("Vivek Kumar");
e2.setSalary(50000);
e2.setBonus(5);
Contract_Employee e3=new Contract_Employee();
e3.setName("Arjun Kumar");
e3.setPay_per_hour(1000);
e3.setContract_duration("15 hours");
session.persist(e1);
session.persist(e2);
session.persist(e3);
t.commit();
session.close();
System.out.println("success");
}
}
Table Per Subclass using Annotation
Table Per Subclass class As we have specified earlier, in case of table per subclass strategy, tables are created as per persistent classes but they are treated using primary and foreign key. So there will not be any duplicate column in the relation.
We need to specify @Inheritance(strategy=InheritanceType.JOINED) in the parent class and @PrimaryKeyJoinColumn annotation in the subclasses.
Let's see the hierarchy of classes that we are going to map.
File: Employee.java
import javax.persistence.*;
@Entity
@Table(name = "employee103")
@Inheritance(strategy=InheritanceType.JOINED)
public class Employee {
@Id
@GeneratedValue(strategy=GenerationType.AUTO)
@Column(name = "id")
private int id;
@Column(name = "name")
private String name;
//setters and getters
}
File: Regular_Employee.java
import javax.persistence.*;
@Entity
@Table(name="regularemployee103")
@PrimaryKeyJoinColumn(name="ID")
public class Regular_Employee extends Employee{
@Column(name="salary")
private float salary;
@Column(name="bonus")
private int bonus;
//setters and getters
}
File: Contract_Employee.java
import javax.persistence.*;
@Entity
@Table(name="contractemployee103")
@PrimaryKeyJoinColumn(name="ID")
public class Contract_Employee extends Employee{
@Column(name="pay_per_hour")
private float pay_per_hour;
@Column(name="contract_duration")
private String contract_duration;
//setters and getters
}
public class StoreData {
public static void main(String args[])
{
StandardServiceRegistry ssr = new StandardServiceRegistryBuilder().configure("hibernate.cfg.xml").build();
Metadata meta = new MetadataSources(ssr).getMetadataBuilder().build();
SessionFactory factory=meta.getSessionFactoryBuilder().build();
Session session=factory.openSession();
Transaction t=session.beginTransaction();
Employee e1=new Employee();
e1.setName("Gaurav Chawla");
Regular_Employee e2=new Regular_Employee();
e2.setName("Vivek Kumar");
e2.setSalary(50000);
e2.setBonus(5);
Contract_Employee e3=new Contract_Employee();
e3.setName("Arjun Kumar");
e3.setPay_per_hour(1000);
e3.setContract_duration("15 hours");
session.persist(e1);
session.persist(e2);
session.persist(e3);
t.commit();
session.close();
System.out.println("success");
}
}
Hibernate Relationship One-to-One One-Many many-many One to one annoatation =============
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