Question

Can anyone help me understand why the piece of code below returns no results from the query yet the second sample does (though woe betide me if I try to use criteria on the second one!)

 type EbayData = 
    ODataService<"http://ebayodata.cloudapp.net">

let Ebay = EbayData.GetDataContext()

let Favourites title number = query{
    for deal in Ebay.Deals do
    where (deal.Title.Contains(title))
    take number
    }


let Esearch title number =  [for item in Favourites title number do 
                                  yield item]

The working version:

type Catalog = ODataService< "http://ebayodata.cloudapp.net/" >

let ebay = Catalog.GetDataContext()

let trial =
            [ for item in ebay.Deals do
               yield item]

I can’t seem to output the first to any kind of list, no matter what do with |> etc. The second sample doesn’t seem to bring back many resuls to do a text query on. However, my real issue is I can’t seem to get anything out of the LINQ in F# version.

The output is used in a WPF application where I use VB to talk to the list. I have populated a non discriminated list of 10 items with it, so that end does work. This is the VB code.

 For Each Deal In trial.Where(Function(p) p.Title.Contains(title.Text))
                DealResults.Items.Add(buildStackPanel(Deal))
            Next

The spacing for the F Sharp on this post doesn’t seem to work when I hit Ctrl-K so if anyone can tell me what I’m doing wrong – I guess that’s a second question!

Answer 1

I don’t know why this is not working for you. I knocked out the following and it seems to work:

open Microsoft.FSharp.Data
type Catalog = TypeProviders.ODataService< "http://ebayodata.cloudapp.net/" >

let ebay = Catalog.GetDataContext()

let trial =
            [ for item in ebay.Deals do
               yield item]
let trial2 = query {
                for deal in ebay.Deals do
                where (deal.Title.Contains "a")
                take 2
             }
let ESearch title number =
             query {
                for deal in ebay.Deals do
                where (deal.Title.Contains title)
                take number
             }

[<EntryPoint>]
let main argv = 
    trial |> Seq.take 2 |> Seq.iter (fun d -> printfn "%s" d.Title)
    trial2 |> Seq.iter (fun d -> printfn "%s" d.Title)
    ESearch "a" 2 |> Seq.iter (fun d -> printfn "%s" d.Title)

    0

Maybe you tried searching for stuff that doesn’t exist? At the moment there are only 6 deals, so this is not unlikely.

Querying Items

Read about the eBay OData service here: http://ebayodata.cloudapp.net/docs
It has special needs when querying for Items:

(search parameter or $filter with Seller, PrimaryCategoryId or
SecondaryCategoryId is required)

So to query Items, you’ll need to provide at least a search phrase. Your where statement doesn’t get translated to a search parameter in the final url. To add custom parameters in this Type Provider, you do .AddQueryOption.

let ItemSearch title number =
             query {
                for item in ebay.Items
                             .AddQueryOption("search", title) do
                take number
             }
// use
ItemSearch "wario" 2 |> Seq.iter (fun d -> printfn "%s" d.Title)