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Trying to integrate Microsoft OData v4 stack with Mongo C# Driver. I would like to expose a Mongo collection and enable the OData $filter operation against the fields contained in the ExtraElements dictionary.

I have created a minimal example of the issue. Beginning with an empty WebAPI project in Visual Studio 2015, I created the following model:

  public class TestEntity

  {

    [BsonId, BsonRepresentation(BsonType.ObjectId)]

    public string _id { get; set; }



    public string Id { get; set; }



    [BsonExtraElements]

    public Dictionary<string, object> ExtraElements { get; set; }

  }

I exposed EDM EntitySet via OData by adding the following at the end of WebApiConfig.Register() method:

  // OData

  var edmBuilder = new ODataConventionModelBuilder();

  edmBuilder.EntitySet<TestEntity>("test");



  config.MapODataServiceRoute("odata", "odata", edmBuilder.GetEdmModel());

Finally, I created a simple TestController:

  public class TestController : ODataController

  {

    [EnableQuery(AllowedFunctions = Microsoft.AspNet.OData.Query.AllowedFunctions.All)]

    public IQueryable<TestEntity> Get()

    {

      var mongo = new MongoClient();

      var db = mongo.GetDatabase("test");

      var collection = db.GetCollection<TestEntity>("test");

      var result = collection.AsQueryable() as IQueryable<TestEntity>;

      return result;

    }

  }

I added an actual object to the Mongo collection:

> db.test.insert( {Id:'test', Name:'testName'})                                                   WriteResult({ "nInserted" : 1 })

> db.test.find()

{ "_id" : ObjectId("5c266040fd7e5a3c63b33cd8"), "Id" : "test", "Name" : "testName" }

Now I can query find as long as I don't try to use $filter on the ExtraElements:

http://localhost:63927/odata/test

{"@odata.context":"http://localhost:63927/odata/$metadata#test","value":[{"Id":"test","Name":"testName","_id":"5c266040fd7e5a3c63b33cd8"}]}

However, if I try to filter against the Name (one of the ExtraElements) the following error occurs:

http://localhost:63927/odata/test?$filter=Name%20eq%20%27testName%27

Message: Convert(IIF((({document}{ExtraElements} != null) AndAlso {document}{ExtraElements}.ContainsKey("Name")), {document}{ExtraElements}.Item["Name"], null)) is not supported.



Exception: System.InvalidOperationException



Stack Trace:

   at MongoDB.Driver.Linq.Translators.PredicateTranslator.GetFieldExpression(Expression expression)

   at MongoDB.Driver.Linq.Translators.PredicateTranslator.TranslateComparison(Expression variableExpression, ExpressionType operatorType, ConstantExpression constantExpression)

   at MongoDB.Driver.Linq.Translators.PredicateTranslator.Translate(Expression node)

   at MongoDB.Driver.Linq.Translators.PredicateTranslator.Translate(Expression node, IBsonSerializerRegistry serializerRegistry)

   at MongoDB.Driver.Linq.Translators.QueryableTranslator.TranslateWhere(WhereExpression node)

   at MongoDB.Driver.Linq.Translators.QueryableTranslator.TranslatePipeline(PipelineExpression node)

   at MongoDB.Driver.Linq.Translators.QueryableTranslator.Translate(Expression node, IBsonSerializerRegistry serializerRegistry, ExpressionTranslationOptions translationOptions)

   at MongoDB.Driver.Linq.MongoQueryProviderImpl`1.Execute(Expression expression)

   at MongoDB.Driver.Linq.MongoQueryableImpl`2.GetEnumerator()

   at Microsoft.AspNet.OData.Formatter.Serialization.ODataResourceSetSerializer.WriteResourceSet(IEnumerable enumerable, IEdmTypeReference resourceSetType, ODataWriter writer, ODataSerializerContext writeContext)

   at Microsoft.AspNet.OData.Formatter.ODataOutputFormatterHelper.WriteToStream(Type type, Object value, IEdmModel model, ODataVersion version, Uri baseAddress, MediaTypeHeaderValue contentType, IWebApiUrlHelper internaUrlHelper, IWebApiRequestMessage internalRequest, IWebApiHeaders internalRequestHeaders, Func`2 getODataMessageWrapper, Func`2 getEdmTypeSerializer, Func`2 getODataPayloadSerializer, Func`1 getODataSerializerContext)

   at Microsoft.AspNet.OData.Formatter.ODataMediaTypeFormatter.WriteToStreamAsync(Type type, Object value, Stream writeStream, HttpContent content, TransportContext transportContext, CancellationToken cancellationToken)

--- End of stack trace from previous location where exception was thrown ---

   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()

   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)

   at System.Web.Http.WebHost.HttpControllerHandler.<WriteBufferedResponseContentAsync>d__1b.MoveNext()

If I add a property such as public string Name { get; set; } to the TestEntity class then the filtering will work as expected, however, I am seeking a solution which allows filtering on the BsonExtraElements.