Table Per Subclass using Annotation
As we have specified earlier, in case of table per subclass strategy, tables are created as per persistent classes but they are reated using primary and foreign key. So there will not be duplicate columns 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.
The table structure for each table will be as follows:
Table structure for Employee class
Table structure for Regular_Employee class
Table structure for Contract_Employee class
Example of Table per subclass class using Annotation
In this example we are creating the three classes and provide mapping of these classes in the employee.hbm.xml file.
1) Create the Persistent classes
You need to create the persistent classes representing the inheritance. Let's create the three classes for the above hierarchy:File: Employee.java File: Regular_Employee.java File: Contract_Employee.java
2) create configuration file
Open the hibernate.cgf.xml file, and add an entry of mapping resource like this:
Now the configuration file will look like this:File: hibernate.cfg.xml
The hbm2ddl.auto property is defined for creating automatic table in the database.
3) Create the class that stores the persistent object
In this class, we are simply storing the employee objects in the database.File: StoreData.java