Aspect-Oriented Programming : Aspect-Oriented Programming with the RealProxy Class

A well-architected application has separate layers so different concerns don’t interact more than needed. Imagine you’re designing a loosely coupled and maintainable application,but in the middle of the development,you see some requirements that might not fit well in the architecture,such as:

• The application must have an authentication system,used before any query or update.
• The data must be validated before it’s written to the database.
• The application must have auditing and logging for sensible operations.
• The application must maintain a debugging log to check if operations are OK.
• Some operations must have their performance measured to see if they’re in the desired range.

Any of these requirements need a lot of work and,more than that,code duplication. You have to add the same code in many parts of the system,which goes against the “don’t repeat yourself” (DRY) principle and makes maintenance more difficult. Any requirement change causes a massive change in the program. When I have to add something like that in my applications,I think,“Why can’t the compiler add this repeated code in multiple places for me?” or,“I wish I had some option to ‘Add logging to this method.’”

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The good news is that something like that does exist:?aspect-oriented programming (AOP). It separates general code from aspects that cross the boundaries of an object or a layer. For example,the application log isn’t tied to any application layer. It applies to the whole program and should be present everywhere. That’s called a crosscutting concern.

AOP is,according to Wikipedia,“a programming paradigm that aims to increase modularity by allowing the separation of crosscutting concerns.” It deals with functionality that occurs in multiple parts of the system and separates it from the core of the application,thus improving separation of concerns while avoiding duplication of code and coupling.

In this article,I’ll explain the basics of AOP and then detail how to make it easier by using a dynamic proxy via the Microsoft .NET Framework class RealProxy.