RavenDB - Avoiding ambiguity in result transformers

Published on 2013-2-25

So, this is a niche case that is quite annoying for people writing transformers as part of a map or a map/reduce index - and now we have the ability to specify transformers separately to the index this problem only gets worse.

What is this problem?

Well, if I make a map that does this:

public class Ponies : AbstractIndexCreationTask<Pony>
{
   public Ponies() {
     Map = ponies =>
           from pony in ponies
           select new {
             pony.Name,
             pony.Colour,
             pony.CutieMark
           }

     Store(pony => pony.CutieMark, FieldStorage.Yes);
     Store(pony => pony.Name, FieldStorage.Yes);
     Store(pony => pony.Colour, FieldStorage.Yes);
   }
}

Available to me without even loading the document after performing a query, is "Name", "Colour", and "CutieMark". Obviously we can store other things in there as well, and so some funky things in the map - but this is the essence of this functionality.

The same thing happens by default when you apply a reduce stage to an index, because you lose the original document entirely because of aggregation.

This can be a bit confusing, as sometimes you want the result from that store data, and sometimes you want the data from the document, and this has been an all-or-nothing thing.

Now we can Use Load<> with a ResultTransformer, this is even more ambiguous.

So, from now on, whenever you access anything in a ResultTransformer, RavenDB will first look in the stored fields for the information, and if not found - will load the document associated with the current result and fetch it from that.

It's a small change, but one which will remove a lot of the confusion around this feature.

This used to ask if you wanted to hire me

But chances are I'm not available, as I'm busy shipping stuff.

I am available for conference speaking, I like talking and will do so for just T&E (and perhaps a bottle of wine or two).

I have done soft keynotes, and usually entertain/rile people in equal proportion, but prefer to talk tech as that's what I do

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