Question

I am working through a tutorial ‘Professional ASP.NET MVC 3’ by J Galloway. In this tutorial, Jon shows us how to build the MVC music store.

I am at the part where we are creating CS classes to model the data using EF code first.

I all the examples in the book, public virtual int property {get; set; } is used with no explanation. The term virtual is stuffed EVERYWHERE.

Elsewhere on the web, I have not seen the term virtual used with any kind of concistency whatsoever.

Could anybody explain to me:

1. The purpose of the term ‘virtual’ in this particular context
2. Is using ‘virtual’ necessary?
3. Why do some people use ‘virtual’ and others do not?
4. Why do some people only use ‘virtual’ when defining foreign keys?
5. What is the best practice use of the term ‘virtual’?

Many thanks in advance

Answer 1

In order to truly understand the virtual keyword you are going to want to read up on Polymorphism in general:

Polymorphism is often referred to as the third pillar of
object-oriented programming, after encapsulation and inheritance.
Polymorphism is a Greek word that means “many-shaped” and it has two
distinct aspects:

1. At run time, objects of a derived class may be treated as objects of a
   base class in places such as method parameters and collections or
   arrays. When this occurs, the object’s declared type is no longer
   identical to its run-time type.

2. Base classes may define and implement virtual methods, and derived
   classes can override them, which means they provide their own
   definition and implementation. At run-time, when client code calls the
   method, the CLR looks up the run-time type of the object, and invokes
   that override of the virtual method. Thus in your source code you can
   call a method on a base class, and cause a derived class’s version of
   the method to be executed.

Once you understand these concepts better you might be able to determine whether or not the method you are creating from the book needs to be virtual or not.