Returning derived types in OData

Question

Here is my code using ODatav4:

WebApiConfig.cs

ODataConventionModelBuilder builder = new ODataConventionModelBuilder();

builder.EntitySet<PurchaseBaseDTO>("Purchases");
builder.EntityType<PurchaseBaseDTO>().Filter();
builder.EntityType<PurchaseBaseDTO>().Expand();
builder.EntityType<PurchaseBaseDTO>().OrderBy();
builder.EntityType<PurchaseBaseDTO>().Count();
builder.EntityType<PurchaseBaseDTO>().Page(50, 999999);

config.MapODataServiceRoute(
            routeName: "myRoute",
            routePrefix: "api",
            model: builder.GetEdmModel()
            );

FluentValidationModelValidatorProvider.Configure(config);

PurchasesController.cs

public class PurchasesController : ODataController
{
    readonly PurchaseService pgs = new PurchaseService();

    [EnableQuery]
    public IQueryable<PurchaseSimpleDTO> Get()
    {
        return pgs.Get();
    }

    [EnableQuery]
    public SingleResult<PurchaseComplexDTO> Get([FromODataUri] int key)
    {
        return SingleResult.Create(pgs.Get(key));
    }
}

PurchaseBaseDTO.cs

public abstract class PurchaseGoodsBaseDTO
{
    public int Id { get; set; }
}

PurchaseSimpleDTO.cs

public class PurchaseGoodsSimpleDTO : PurchaseGoodsBaseDTO
{
    [AutoExpand]
    public ActionTaker Supplier { get; set; }
}

ActionTaker.cs

public class ActionTaker
{
    public int Id { get; set; }
    public string Name { get; set; }
}

PurchaseComplexDTO.cs

public class PurchaseGoodsComplexDTO : PurchaseGoodsBaseDTO
{
    public decimal AmountPurchased { get; set; }
    public string PurchaseUnit { get; set; }
    public decimal Price { get; set; }

    public string CreatedBy { get; set; }
    public DateTime CreatedAt { get; set; }
    public string ModifiedBy { get; set; }
    public DateTime? ModifiedAt { get; set; }
}

In PurchaseService I simply create those objects and assign fields values. I return IQueryable<T> in both methods with respective Simple or Complex version of DTO.

Running http://localhost:64502/api/Purchases?$top=10&$skip=0&$count=true returns list of purchases from database, everything is OK.

Running http://localhost:64502/api/Purchases(1) returns

"error": {
    "code": "",
    "message": "The query specified in the URI is not valid. Encountered invalid type cast. 'PurchaseSimpleDTO' is not assignable from 'PurchaseComplexDTO'.",
    "innererror": {
        "message": "Encountered invalid type cast. 'PurchaseSimpleDTO' is not assignable from 'PurchaseComplexDTO'.",
        "type": "Microsoft.OData.ODataException",
        "stacktrace": "   w Microsoft.OData.UriParser.UriEdmHelpers.CheckRelatedTo(IEdmType parentType, IEdmType childType)\r\n   w Microsoft.OData.UriParser.SelectExpandPathBinder.FollowTypeSegments(PathSegmentToken firstTypeToken, IEdmModel model, Int32 maxDepth, ODataUriResolver resolver, IEdmStructuredType& currentLevelType, PathSegmentToken& firstNonTypeToken)\r\n   w Microsoft.OData.UriParser.SelectExpandBinder.GenerateExpandItem(ExpandTermToken tokenIn)\r\n   w System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext()\r\n   w System.Linq.Enumerable.WhereEnumerableIterator`1.MoveNext()\r\n   w System.Collections.Generic.List`1.InsertRange(Int32 index, IEnumerable`1 collection)\r\n   w Microsoft.OData.UriParser.SelectExpandBinder.Bind(ExpandToken expandToken, SelectToken selectToken)\r\n   w Microsoft.OData.UriParser.SelectExpandSemanticBinder.Bind(ODataPathInfo odataPathInfo, ExpandToken expandToken, SelectToken selectToken, ODataUriParserConfiguration configuration, BindingState state)\r\n   w Microsoft.OData.UriParser.ODataQueryOptionParser.ParseSelectAndExpandImplementation(String select, String expand, ODataUriParserConfiguration configuration, ODataPathInfo odataPathInfo)\r\n   w Microsoft.OData.UriParser.ODataQueryOptionParser.ParseSelectAndExpand()\r\n   w Microsoft.AspNet.OData.Query.SelectExpandQueryOption.ProcessLevels()\r\n   w Microsoft.AspNet.OData.Query.SelectExpandQueryOption.get_ProcessedSelectExpandClause()\r\n   w Microsoft.AspNet.OData.Query.ODataQueryOptions.ApplySelectExpand[T](T entity, ODataQuerySettings querySettings)\r\n   w Microsoft.AspNet.OData.Query.ODataQueryOptions.ApplyTo(IQueryable query, ODataQuerySettings querySettings)\r\n   w Microsoft.AspNet.OData.EnableQueryAttribute.ApplyQuery(IQueryable queryable, ODataQueryOptions queryOptions)\r\n   w Microsoft.AspNet.OData.EnableQueryAttribute.ExecuteQuery(Object responseValue, IQueryable singleResultCollection, IWebApiActionDescriptor actionDescriptor, Func`2 modelFunction, IWebApiRequestMessage request, Func`2 createQueryOptionFunction)\r\n   w Microsoft.AspNet.OData.EnableQueryAttribute.OnActionExecuted(Object responseValue, IQueryable singleResultCollection, IWebApiActionDescriptor actionDescriptor, IWebApiRequestMessage request, Func`2 modelFunction, Func`2 createQueryOptionFunction, Action`1 createResponseAction, Action`3 createErrorAction)"
    }
}

What I already tried:

I analyzed this (among many other less relevant) thread and I can't find many differences, at least none important, if I'm correct.

I tried to return PurchaseComplexDTO instead of SingleResult<PurchaseComplexDTO> .

I tried to return IQueryable<PurchaseComplexDTO> instead of SingleResult<PurchaseComplexDTO> .

I tried to change return typed of both methods in controller to PurchaseBaseDTO .

Nothing helped. Where is my mistake?

Answer 1

This is only speculation, but have you tried to use Attribute Routing? The problem here is that your EdmModel is specifying the base type, but you do not have a corresponding Get method that explicitly matches the convention of having a return type of PurchaseBaseDTO (or IHttpActionResult), a name matching Get and that has a parameter called key

public class PurchasesController : ODataController
{
    readonly PurchaseService pgs = new PurchaseService();

    [EnableQuery]
    public IQueryable<PurchaseSimpleDTO> Get()
    {
        return pgs.Get();
    }

    [ODataRoute("({key})")]
    [EnableQuery]
    public SingleResult<PurchaseComplexDTO> Get([FromODataUri] int key)
    {
        return SingleResult.Create(pgs.Get(key));
    }
}

You will also have to enable attribute routing:

string routePrefix = "api";
var uriConventions = ODataRoutingConventions.CreateDefaultWithAttributeRouting(routePrefix, config);
config.MapODataServiceRoute(
        routeName: "myRoute",
        routePrefix: routePrefix,
        model: builder.GetEdmModel(),
        pathHandler: new DefaultODataPathHandler(),
        routingConventions: uriConventions 
        );config.MapODataServiceRoute("myRoute", routePrefix, model, new DefaultODataPathHandler(), uriConventions);

Answer 2

I changed my second Get method and now it works:

[EnableQuery]
public PurchaseGoodsComplexDTO Get([FromODataUri] int key)
{
    return pgs.Get(key).FirstOrDefault();
}

pgs.Get(key); returns an IQueryable .