Implementing inheritance

Like all object-oriented programming languages, PHP is designed on top of the inheritance concept; however, relational databases are not. This is the common problem when mapping classes to tables.

The Doctrine ORM provides the following three ways to achieve inheritance:

• Mapped Superclasses

• Single Table Inheritance

• Class Table Inheritance

To learn about them, we will create three implementations of the same model, that is, for content authors.

Both posts and comments have authors. Authors must have a name and an e-mail address. Posts' authors (and only them) can also have an optional biography.

To represent this, we will create two classes: PostAuthor and CommentAuthor. They both extend an abstract Author class. Each Comment entity is linked to a CommentAuthor class and each Post entity to a PostAuthor class.

Using Mapped Superclasses

Mapped Superclasses are simple PHP classes that share mapped properties used by their descendant entities. Mapped Superclasses are not entities...