DataServiceContext can't work with POCO's

[wizofaus]

Given the following

        class Product
        {
            public int ID { get; set; }
            public String Name { get; set; }
            public String Description { get; set; }
        }

        class MyContext : DataServiceContext
        {
            public MyContext() : base(new Uri("http://services.odata.org/V4/OData/OData.svc"))
            {
                Products = CreateQuery<Product>("Products");
            }
            public DataServiceQuery<Product> Products { get; set; }
       }

       var count = MyContext().Products.Count();  // this works, returns correct result
       var list = MyContext().Products.List(); // this fails, 'The complex type 'System.Object' has no settable properties.'

It would seem there should be enough information for the OData context to be able to parse the result and construct a list of Products with the expected property values read from the JSON.

At first I just got "'The complex type 'System.Object' has no settable properties.'", which makes no sense, as DataServiceQuery is templated and knows perfectly well what type it is for, but anyway I tried setting ResolveType to a delegate that could resolve the types, but nothing I tried worked - if it always returns typeof(Product) for both "Products" and "Product" (the two type names it gets called with), it results in a single empty Product with no properties set, and if it returns a collection type for "Products" that exposes a value indexer, I just get other errors about types not being assignable.

I understand normally you'd use DataServiceContext with an edmx file but I wish to avoid this - is the OData library not designed to be able to work with POCOs the way EntityFramework can, and if so, is there any reason why this wouldn't be a worthwhile feature to add?

[wizofaus]

(As a workaround, it takes about 8 lines of code to do the HTTP fetch manually using the RequestUri exposed by the DataServiceQuery and deserialize using Json.net, so I'm OK with this now for now, but it does seem odd that it doesn't just work as is).

[wizofaus]

As part of this I was able to also fix the problem that the existing library can't handle collection.FirstOrDefault(<predicate>) (or .Count(<predicate>) etc.).
I was able to do this just by transforming the expression tree before creating the DataServiceQuery.
It's certainly not a bullet-proof solution at this point, but is there any reason the library doesn't natively support this?

[wizofaus]

I've also managed now to implement

collections.Select(p => p.<member>)

Which required some real trickery as currently the OData library can only generate the right query if you use an anonymous type collections.Select(p => new { <member> = p.<member> }) and trying to build an expression tree for a type that doesn't exist is somewhat challenging (fortunately it doesn't actually have to exist, it just has to have the necessary properties for the tree to be parsed and transformed correctly). Again, seems odd the library doesn't natively support this, as it severely limits the usefulness of LINQ->OData.

[pmatrasc]

@wizofaus

While they work on the fix, would you please share some code snippets to better understand how you worked around the last two issues you listed?

Thanks!

[julealgon]

I'm also very interested in seeing your solution to the problem @wizofaus . I'd appreciate if you could share it here.

Right now I've resorted to the Simple.OData.Client library to interface with my OData service. As long as you have the $metadata endpoint properly exposed, it works fine with POCO classes.

[wizofaus]

I'll have to dig out the code, it's being lying dormant for while, but sure, happy to share it.