Querying WCF endpoints using Web API

Querying WCF endpoints using Web API

May 19, 2011 9:46 pm

In previous versions of the Web API, you could query your REST endpoints that exposed an IQueryable server-side, kinda “Linq to WCF” as [@gblock](<http://twitter.com/#!/gblock>) said. This was immensely useful and an important driver (among others) for me to move away from ~~Astoria~~ ADO.NET Data Services. That functionality is [gone](<http://twitter.com/#!/gblock/status/70315843627659264>) now ([vote to get it back](<http://wcf.codeplex.com/workitem/41>)!).

So I was wondering how to bring it back. Would I need to refactor the monstrous (as in big, not ugly) OData client source to reuse just the Uri query translator? This started to look like a daunting task.

Fortunately, after a few back & forth and spelunking in Reflector and the source code, I figured out a way to essentially reuse the entire query translator from the OData services client (built-in .NET 4.0 in the System.Data.Services.Client namespace) and layer it on top of the HttpClient. Awesomeness ensued . Here’s a test from the NETFx NuGet that shows how it works:

[Fact]
public void WhenQuerying_ThenGetsResponse()
{
    var config = HttpHostConfiguration.Create();
    config.Configuration.OperationHandlerFactory.Formatters.Insert(0, new JsonNetMediaTypeFormatter());

    using (var ws = new HttpWebService<TestService>("http://localhost:20000", "products", config))
    {
        var client = new HttpClient("http://localhost:20000");
        client.DefaultRequestHeaders.Accept.Add(new System.Net.Http.Headers.MediaTypeWithQualityHeaderValue("text/json"));

        // THIS IS THE DEAL!
        var response = client.Query<Product>("products", x => x.Id <= 2);

        Assert.True(response.IsSuccessStatusCode);

        var products = new JsonSerializer().Deserialize<List<Product>>(new JsonTextReader(new StreamReader(response.Content.ContentReadStream)));

        Assert.Equal(2, products.Count);
        Assert.True(products.All(x => x.Id <= 2));
    }
}

And it even works for sub-properties of the main resource:

var response = client.Query<Product>("products", x => x.Owner.Name == "kzu");

Assert.True(response.IsSuccessStatusCode);

var products = new JsonSerializer().Deserialize<List<Product>>(new JsonTextReader(new StreamReader(response.Content.ContentReadStream)));

Assert.Equal(2, products.Count);
Assert.True(products.All(x => x.Owner.Name == "kzu"));

Yay!

Note that this is a low-level API that follows HttpClient approach: it knows nothing about deserializing the payloads into entities or supported content types, etc. That’s another nuget that’s coming, the HttpEntityClient . Stay tunned.

Enjoy this one by searching for HttpClient (or HttpClientQuery) in the Library Reference dialog:

/kzu