Friday, 27 February 2015

Abstractions

This is the first part of my series on abstractions.


Coupling is one of the enemies of a healthy code base. One way to combat high coupling is to introduce abstractions.

Too few abstractions is bad. Your code can become coupled. Some of the worst code I've worked with was highly coupled to either the database, UI or both. Working with such code is difficult.

Too many abstractions is equally as bad. Abstraction behind abstraction can become so difficult to work with the benefit of abstracting in the first place is lost. Some of the worst code I've worked with was so convoluted with needless abstractions it made any development a tricky process.

Most abstractions are not really abstractions at all, but nothing more than simple indirection. Indirection is sometimes required, though it is wrong to confuse with abstraction. IFileWriter is not an abstraction. IReciept that happens to write to the file system when implemented as FileSystemReceipt is an abstraction. IFileWriter could be an abstraction if the software we were writing involved working directly with the file system, such as a text editor. In the case of printing receipts, where they are printed is simply an implementation detail.

Finding a balance between the right level of abstraction can be tricky. From my experience there a few techniques that can be used.

Techniques

Embrace Coupling

Udi Dahan makes this point in his presentations. If you have a traditional application with a UI, domain and data layer why bother adding further layers to abstract these? If we wish to retrieve a new field from the database and display the value we have three places to change, adding further models and mapping layers does nothing but increase coupling. Applying namespaces correctly can also help here, if everything that needs to change at the same time is logically grouped, such changes are easier.

Apply YAGNI

Do you truly need a database model mapped into a domain model, mapped into a view model and back? Applying YAGNI can limit many abstractions by simply not worrying about "what if" scenarios until they actually occur.

CQRS

Command Query Responsibility Separation or CQRS deserves an explanation on its own, but for now applying CQRS reduces unnecessary coupling by embracing it. For querying data and displaying it on a screen my default choice is to use CQRS to simply read from the database and populate a view model. This limits abstractions and helps keep the code focused, flexible and open to change. I will expand on CQRS in a future post.

No comments:

Post a Comment