How to query RavenDB using complex query in F#

Question

I am using RavenDB 2.0 unstable. Is it possible to query RavenDB 2.0 with a lambda or similar technique (linq?) from F#?

Here is intent example code. I am attempting to get all the posts in last 72 hours. Its wrong, but it gets the idea across.

static member public GetTopPosts _ =
    use store = (new DocumentStore(Url = Docs.serverUrl, DefaultDatabase = Docs.dbName )).Initialize()
    use session = store.OpenSession()
    let result = session.Query<Post>().Where(fun x -> x.Date > DateTime.Now - new TimeSpan(72,0,0))
    ...

How can something like this be accomplished?

Answer 1

Yes you can do this.

You can find an example of this in FAKE

In your case your query would look something like this

let getTopPostsAsOf date =
    use session = docStore.OpenSession()
    query {
       for post in session.Query<Post>() do
       where (post.Date > date)
       select post
    } |> Seq.toArray

this would then be called with

let result = getTopPostsAsOf (DateTime.Now - TimeSpan.FromHours(72))

A couple of things to note.

1. The DocumentStore should be created once and only once at the startup of the application.

2. Also typically only a small set of library calls can be used within the query expressions, hence why I pass in the already computed date. The reason for this is because these expression trees end up getting serialized and executed within raven db engine.