Awesome RavenDB Feature: Eval Patching, Part II–Denormalized References

I mentioned yesterday that I am keeping the best for today. What I am going to show you is how you can use Eval Patching for keeping track of denormalized references.

In this case, we have Users & Posts. Each Post contains a UserName property as well as the user id. When the user changes his name, we need to update all of the relevant posts.

Here is how you can do this:

store.DatabaseCommands.UpdateByIndex("Posts/ByUser",
    new IndexQuery{Query = "UserId:" + userId},
    new AdvancedPatchRequest
        {
            Script = @"
var user = LoadDocument(this.UserId);
this.UserName = user.Name;
"
        });

And this is a really simple scenario, the options that this opens, the ability to load a separate document and modify the current document based on its value is really powerful.