Today I was helping on a project which was using ADO.NET SQL Client. Wow, it looks so much scary, and old. I was asked to do some tweaks, so that data layer could be organized. Can I use Repository pattern here, one of the ways to add separation of responsibility these days.
So I started on creating a base class for these repositories. I thought of managing all connection related code in that base class. That was quite easy when I moved ExecuteNonQuery related calls here. Next came the hardest part ExecuteReader, how to send back DataReader without loosing control on my connection state. I can not move all reader related usage in base class, that would negate single responsibility rule.
Hmm, one way would be to create a virtual method in base class, and then each inherited class can override and implement it’s own mapping rules in it. I did small test with that, but soon was struck, what about mapping compositions. If I used this approach then I will have to add multiple conditional cases to map each item properly.
Then I thought of passing in mapper related methods as delegate, not bad. But why not use new concepts, Action<T, T …> / Func<T, …, TResult> / Predicate<T, …, bool>.
I wrote a small application to test this, here is it’s code.
Here is the model I will be using
This is what base class will look
How I used this to construct my concrete class
Look how many mapping options I have using this technique. It looks quite amazing, ha.
How would you handle if there is a collection inside an entity as mentioned in http://stackoverflow.com/questions/20699004/grouping-a-collection?