Comments on: DefaultValue attribute for Castle MonoRail

By: Tigraine » Blog Archive » How MonoRail selects it’s best ActionMethod candidate: CalculateParamPoints

Thu, 27 Aug 2009 13:47:22 +0000

[...] Curran pointed me at one interesting flaw with my implementation of the DefaultValueAttribute for MonoRail I blogged [...]

By: James Curran

James Curran — Wed, 26 Aug 2009 13:44:14 +0000

Thinking about this more, you are right.

If we return 0, then
/Home/Browser.rails?page=2
would probably be a non-match for
public void Browse([DefaultValue("beer")] string category, int page)
which is not what we want.
However, if we return 10, then for
/Home/Browser.rails?page=2&source=db
then
public void Browse([DefaultValue("beer")] string category, int page)
and
public void Browse(int page, string source)
become equally good, which is also not what we want.

I think always returning 5 may work best, but mostly I think that this is going to require a bit more investigation of how CalculateParamPoints works. (I smell at least one of us getting a blog post out of that)

By: Daniel Hölbling

Daniel Hölbling — Tue, 25 Aug 2009 19:48:31 +0000

Hmm.. actually a tough question.
I’m not totally sold on making it’s weight 0. I see your point with the DefaultValue being a value after all so it shouldn’t matter if a parameter is passed or not, but setting it to 0 would also take away all the weight from that method overload..

I’ll think about it a bit further and maybe we’ll continue this discussion on the castle mailing list

Anyway, thanks for your comment!

By: Daniel Hölbling

Daniel Hölbling — Tue, 25 Aug 2009 19:07:05 +0000

Very good point. I’ll try that out and possibly update the post.

By: James Curran

James Curran — Tue, 25 Aug 2009 19:05:09 +0000

I not sure about this, (as neither you nor Ken really explains CalculateParamPoints), but I think you are saying that, given the method:

public void Browse([DefaultValue("beer")] string category, int page)

then,
/Home/Browser.rails?category=xxxx&page=2

is a better match for that method than

/Home/Browser.rails?page=2

However, with the DefaultValue, both are equally good. The DefaultValue attribute shouldn’t affect how good a match a request is to a method, so it really should just return 0 for everything.