OpenData.Core is a C# library which parses an OData query uri into an object model which can be used to query custom data sources which are not IQueryable.

To use it in your own Web API you need to install the nuget package Install-Package OpenData.Core

Somewhere in your application startup/webapi configuration, specify the types which will be used for OData queries:

public static class WebApiConfig
{
    public static void Register(HttpConfiguration config)
    {
        // Wire-up OData and define the Entity Data Model
        config.UseOData(entityDataModelBuilder =>
        {
            entityDataModelBuilder.RegisterEntitySet<Category>("Categories", x => x.Name);
            entityDataModelBuilder.RegisterEntitySet<Employee>("Employees", x => x.EmailAddress);
            entityDataModelBuilder.RegisterEntitySet<Order>("Orders", x => x.OrderId);
            entityDataModelBuilder.RegisterEntitySet<Product>("Products", x => x.Name);
        });

        // Use Attribute Mapping for the OData controllers
        config.MapHttpAttributeRoutes();
    }
}

Note that when you register an Entity Set, you also specify the name of the Entity Set. The name needs to match the URL you intend to use so if you use http://myservice/odata/Products then register the Entity Set using .RegisterEntitySet<Product>("Products", x => x.Name);, if you use http://myservice/odata/Product then register the Entity Set using .RegisterEntitySet<Product>("Product", x => x.Name);.

In your controller(s), define a Get method which accepts a single parameter of ODataQueryOptions:

public IEnumerable<Category> Get(ODataQueryOptions queryOptions)
{
    // Implement query logic.
}

The library supports OData 4.0