The Hibernate Inheritance Mechanism - 1

Table per Concrete Class + Implicit Polymorphism
 This is the technique with minimum development efforts. The technique follows the below simple steps:

1. For each concrete class, one table is created. 
2. All the inherited properties are mapped in each of these tables.
3. The abstract (base) class is not represented in SQL

The Hibernate Inheritance Mechanism - Preview

Inheritance which is one of the pillars of Object Oriented Programming Model isn't a big player in the SQL environment. While Objects can form both IS-A and HAS-A relationships, Tables are only aware of HAS-A  relationships. (for e.g. 1 Person has many Vehicles)

Hibernate provides techniques that allows us to represents Tables via inheritance relationships. Hibernate has 4 different approaches:

Composite Identifiers

In the previous discussions of identifiers the focus was on implementing surrogate keys as means to uniquely identify the records.
The wikipedia definition of surrogate key states that
"A surrogate key in a database is a unique identifier for either an entity in the modeled world or an object in the database. The surrogate key is not derived from application data."

Bidirectional Components

Components in Hibernate can include a back-reference that allows them to link back to their owning Entity. I decided to try this out and for this created a simple Person entity that includes a name and an Address.

Creating a Hibernate Custom Type - 4

Let us look at the EnhancedUserType.This interface extends the UserType interface and provides additional methods to allow usage in XML representation. I shall implement a type that will allow saving of Enums directly to the database.