Porting MVC Music Store to RavenStoreManagerController, part 2
time to read 3 min | 409 words

There are two methods in StoreManagerController that we haven’t touched yet. Dealing with them is going to just a little bit different:

image

Can you figure out why?

The answer is that when we started, we decided that there really isn’t any reason to store artists as individual documents. They are just reference data, after all. Now, however, we need to reference them.

We could, of course, create a set of artists documents, at which point it would be very easy to port the code:

image

But I still think that artists don’t really exists in this model as an independent entity. So instead of going with this route, we are going to project them.

We define the “Arists” index using the following map/reduce linq queries:

// map 
from album in docs.Albums
select new { album.Artist.Id, album.Artist.Name }

// reduce 
from artist in results
group artist by new { artist.Id, artist.Name } into g
select new { g.Key.Id, g.Key.Name }

If you’ll look carefully, you’ll notice that this is essentially doing a distinct over all the artists across all albums.

And that means that we can now write the code for those two methods like this;

image

There is one very important things to remember here: In Raven’s queries are cheap, because Raven allows you to query indexes only, and those indexes are built in the background, making queries tend to be very fast.

That changes the way that you think about designing you system and data model. You want to move a lot of your processing to indexes and queries upon those indexes, because it tends to be cheaper all around.

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More posts in "Porting MVC Music Store to Raven" series:

  1. (31 May 2010) StoreManagerController, part 2
  2. (29 May 2010) StoreManagerController
  3. (28 May 2010) Porting the checkout process
  4. (25 May 2010) StoreController
  5. (24 May 2010) Advanced Migrations
  6. (23 May 2010) Migrations
  7. (22 May 2010) Porting the HomeController, the Right Way
  8. (21 May 2010) Porting the HomeController, the map/reduce way
  9. (20 May 2010) Data migration
  10. (19 May 2010) Setting up the application
  11. (18 May 2010) The data model