HIbernate - Inheritance – Strategy 3 ( with Annotation ) : Table Per Concrete Class Hierarchy

HIbernate - Inheritance – Strategy 3 ( with Annotation ) : Table Per Concrete Class Hierarchy 

Third Hibernate Annotation Application ( Inheritance – Strategy 3 : Table Per Class Hierarchy ) 

Inheritance Mapping

Hibernate supports 3 basic inheritance mapping strategies.

          1. Table per class hierarchy 
          2. Table per subclass 

          3. Table per concrete class  As per the below example there will be 3 tables and no relations to each other. There is no null values in the table since tables are created per class.  Disadvantage of this approach is, it created duplicate columns.  For this example we use below assotations.  @Inheritance( strategy = InheritanceType.TABLE_PER_CLASS)

• specifies we use Table per class strategy.
• This specified only in the Parent class.

@AttributeOverrides({

@AttributeOverride( name = "empId", column = @Column(name = "empId")),
@AttributeOverride( name = "firstName", column = @Column(name = "firstName")),
@AttributeOverride( name = "lastName", column = @Column(name = "lastName"))
})

- Parent calls attributes got override in Child classes.

  
Suppose you have the base Employee class, with PermanentEmployee and ContractEmployee as subclasses.
 
Steps -

Step 1 - Create POJO classes ( Employee.java and PermanentEmployee, ContractEmployee sub-classes ) Step 2 - Hibernate Configurations ( hibernate.cfg.xml )  Step 3 - Create class to do the execution ( ExecuteEmployee.java ) 
Step 1 - Create POJO classes

 

Create POJO (Plain Old Java Object) classes that represents the Employee, PermanentEmployee and ContractEmployee.

 
 
 

Step 2 - Hibernate Configurations  
 
Create configuration file name as hibernate.cfg.xml and save it. 

 

Step 3 - Create Execute class 

 

Create a ExecuteEmployee class to do the execution.

 

 

 

 

Out put on the above application as follows.