Entity mapping

One of the fundamental tasks in JPA development is to map your domain model entity classes to your database tables and columns. There are two approaches when you are going to design your entities and database in general:

• Designing entity classes and generating a database schema from them
• Designing database tables then implementing entity classes around them

The first approach is only valid and useful when you are starting your application from scratch. Beginning the design with entity classes makes it easier for you, as an application developer, to analyze and design your solution with object-oriented techniques. Note that this may be suitable only for small to medium-scale applications. In large-scale applications, there may be a big database design and implementation team who will take on the database responsibility. In such a case, you have to follow the second approach. Another common case is that the database may exist, as you are going to develop a new vertical application above an existing application, or you are revamping or migrating an existing system to newer technologies.

Anyways, by learning the basic mappings of JPA, you will be able to follow either of these approaches.