How to solve the violations of the Law of Demeter?

Question

A colleague and I designed a system for our customer, and in our opinion we created a nice clean design. But I\'m having problems with some coupling we\'ve introduced. I could t

Answer 1

I think it helps to remember the raison d'être of LoD. That is, if details change in chains of relationships, your code could break. Since the classes you have are abstractions close to the problem domain, then the relations aren't likely to change if the problem stays the same, e.g., Protocol uses Discipline to get its work done, but the abstractions are high level and not likely to change. Think of information hiding, and it's not possible for a Protocol to ignore the existence of Disciplines, right? Maybe I'm off on the domain model understanding...

This link between Protocol and Discipline is different than "implementation" details, such as order of lists, format of data structures, etc. that could change for performance reasons, for example. It's true this is a somewhat gray area.

I think that if you did a domain model, you'd see more coupling than what is in your C# class diagram. [Edit] I added what I suspect are relationships in your problem domain with dashed lines in the following diagram:

On the other hand, you could always refactor your code by applying the Tell, don't ask metaphor:

That is, you should endeavor to tell objects what you want them to do; do not ask them questions about their state, make a decision, and then tell them what to do.

You already refactored the first problem (BLL) with your answer. (Another way to abstract BLL further would be with a rule engine.)

To refactor the second problem (repositories), the inner code

    p.Kind.Discipline.Id == discipline.Id

could probably be replaced by some kind of .equals() call using a standard API for Collections (I'm more of a Java programmer, so I'm not sure of the precise C# equivalent). The idea is to hide the details of how to determine a match.

To refactor the third problem (inside the UI), I'm also not familiar with ASP.NET, but if there's a way to tell a Kind object to return the names of Disciplines (rather than asking it for the details as in Kind.Discipline.Name), that's the way to go to respect LoD.