RavenDB - retrieving part of document

Question

I am playing with Raven DB for few days and I would like to use it as a storage for my Web chat application. I have document which contains some user data and chat history - which is big collection chat messages.

Each time I load user document chat history is also loaded, even if I need only few fields like: user name, password and email.

My question is: how to load only part of document from database ?

Answer 1

Tomek,

You can't load a partial document, but you can load a projection.

session.Query<User>()
   .Where(x=>x.Name == name)
   .Select( x=> new { x.Name, x.Email });

That will load only the appropriate fields

Answer 2

From what I've seen you can do this (based on the original "User" scenario above):

public class UserSummary
{
    public string Name { get; set; }
    public string Email { get; set; }
}

Then you can do this:

documentSession.Query<User>().AsProjection<UserSummary>();

Looking at the Raven server it spits this out as part of the query:

?query=&pageSize=128&fetch=Name&fetch=Email&fetch=Id

So it looks like it is querying and returning only a subset of the original object, which is good.

This also works:

documentSession.Query<User>().Select( x=> new User { Name = x.Name, Email= x.Email })

But I don't think that is as clean as returning a UserSummary object.

Some follow up questions to those who have posted responses:

The link to RaccoonBlog has this example:

https://github.com/ayende/RaccoonBlog/blob/master/RaccoonBlog.Web/Infrastructure/Indexes/PostComments_CreationDate.cs

Would that method be preferred over the .AsProjection()? What is the difference between the two approaches?