Data Layer Best Practices

Question

I am in the middle of a \"discussion\" with a colleague about the best way to implement the data layer in a new application.

One viewpoint is that the data layer should

Answer 1

One trick I've found handy is to have my data layer be "collection agnostic". That is, whenever I want to return a list of objects from my data layer, I get the caller to pass in the list. So instead of this:

public IList GetFoosById(int id) { ... }

I do this:

public void GetFoosById(IList foos, int id) { ... }

This lets me pass in a plain old List if that's all I need, or a more intelligent implementation of IList (like ObservableCollection) if I plan to bind to it from the UI. This technique also lets me return stuff from the method like a ValidationResult containing an error message if one occurred.

This still means that my data layer knows about my object definitions, but it gives me one extra degree of flexibility.