Concepts & Features in NH Prof: Filtering

time to read 3 min | 526 words

A while ago I mentioned the idea of Concepts and Features, I expounded it a bit more in the Feature by Feature post. Concepts and Features is the logical result of applying the Open Closed and Single Responsibility Principles. It boils down to a single requirement:

A feature creation may not involve any design activity.

Please read the original post for details about how this is actually handled. In this case, I wanted to show you how this works in practice with NH Prof. Filtering in NH Prof is a new concept, which allows you to limit what you are seeing in the UI based on some criteria.

The ground work for this feature include the UI for showing the filters, changing the UI to support the actual idea of filtering, and other related stuff. I can already see that we would want to be able to serialize the filters to save them between sessions, but that is part of what the concept is. It is the overall idea.

But once we have the concept outlined, thinking about features related to it is very easy. Let us see how we can build a new filter for NH Prof, one that filter out all the cached statements.

I intentionally choose this filter, because it doesn’t really have any options you need a UI for. Which make my task easier, but here is the UI, FilterByNotCachedView.xaml

		<TextBlock>Uncached statements</TextBlock>

And the filter implementation:

[DisplayName("Not Cached")]
public class FilterByNotCached: StatementFilterBase
	public override bool IsValid
		get { return true; }

	public override Func<IFilterableStatementSnapshot, bool> Process
			return snapshot => snapshot.IsCached == false;

Not hard to figure out what this is doing, I think.

This is all the code required, and NH Prof knows that it is going to pick it up from the appropriate places, and make use of it. This is why after adding these two files, I can now run NH Prof and I get the following:


I don’t think that I can emphasis enough how important this is to enable creating consistent and easy to handle solutions. Moreover, since most requests tend to be for features, rather than concepts, it is extremely easy to put up a new feature.

The end result is that I have a smart infrastructure layer, where I am actually implementing the concepts, and on top of it I am building the actual features. Just to give you an idea, NH Prof currently have just 6 concepts, and everything else is built on top of it.