Fixes #2737: Support getting navigation source for complex types (#2744)

Merging, as no substantive changes were made since Sam's approval.

Author: mikepizzo

src/Microsoft.AspNet.OData.Shared/Formatter/Deserialization/ODataResourceDeserializerHelpers.cs

@@ -66,7 +66,6 @@ internal static ODataDeserializerContext GenerateNestedReadContext(ODataNestedRe
                     segmentType = readContext.Model.FindType(propertyTypeName);
                 }
 
-                // could it be a problem later that the navigationSource is null?
                 DynamicPathSegment pathSegment = new DynamicPathSegment(
                    nestedResourceInfo.Name,
                    segmentType,
@@ -79,12 +78,12 @@ internal static ODataDeserializerContext GenerateNestedReadContext(ODataNestedRe
             {
                 if (edmProperty.PropertyKind == EdmPropertyKind.Navigation)
                 {
-                    Contract.Assert(readContext.Path.NavigationSource != null, "Navigation property segment with null navigationSource");
                     IEdmNavigationProperty navigationProperty = edmProperty as IEdmNavigationProperty;
                     IEdmNavigationSource parentNavigationSource = readContext.Path.NavigationSource;
-                    IEdmNavigationSource navigationSource = parentNavigationSource.FindNavigationTarget(navigationProperty);
+                    IEdmPathExpression bindingPath = GetBindingPath(readContext.Path, navigationProperty);
+                    IEdmNavigationSource navigationSource = parentNavigationSource?.FindNavigationTarget(navigationProperty, bindingPath);
 
-                    if (navigationProperty.ContainsTarget)
+                    if (navigationProperty.ContainsTarget || navigationSource == null || navigationSource is IEdmUnknownEntitySet)
                     {
                         path = AppendToPath(path, new NavigationPropertySegment(navigationProperty, navigationSource), navigationProperty.DeclaringType, parentNavigationSource);
                     }
@@ -110,6 +109,44 @@ internal static ODataDeserializerContext GenerateNestedReadContext(ODataNestedRe
             return BuildNestedContextFromCurrentContext(readContext, path);
         }
 
+        // Determines the binding path for an OData Path to a given navigationProperty
+        private static IEdmPathExpression GetBindingPath(Routing.ODataPath path, IEdmNavigationProperty navigationProperty)
+        {
+            Contract.Assert(navigationProperty != null, "Called GetBindingPath with a null navigation property");
+            if (path == null)
+            {
+                return null;
+            }
+
+            // Binding Path is made up of complex types, containment navigation properties, and type segments
+            List<string> segments = new List<string>();
+            foreach (ODataPathSegment segment in path.Segments)
+            {
+                if (segment is NavigationPropertySegment navSegment)
+                {
+                    segments.Add(navSegment.NavigationProperty.Name);
+                }
+                else if (segment is PropertySegment propertySegment)
+                {
+                    segments.Add(propertySegment.Property.Name);
+                }
+                else if (segment is TypeSegment typeSegment)
+                {
+                    segments.Add(typeSegment.Identifier);
+                }
+            }
+
+            if(navigationProperty.DeclaringType != path.EdmType as IEdmStructuredType)
+            {
+                // Add a type cast segment
+                segments.Add(navigationProperty.DeclaringType.FullTypeName());
+            }
+
+            segments.Add(navigationProperty.Name);
+
+            return new EdmPathExpression(String.Join("/", segments));
+        }
+
         /// <summary>
         /// It builds a nested deserializer context from the current deserializer context
         /// </summary>
@@ -154,11 +191,13 @@ internal static Routing.ODataPath AppendToPath(Routing.ODataPath path, ODataPath
             }
 
             List<ODataPathSegment> segments = new List<ODataPathSegment>(path.Segments);
+            IEdmType pathType = path.EdmType;
 
             // Append type cast segment if required
-            if (declaringType != null && path.EdmType != declaringType)
+            if (declaringType != null && pathType != null && pathType != declaringType
+                && declaringType.IsOrInheritsFrom(pathType.AsElementType()))
             {
-                segments.Add(new TypeSegment(declaringType, navigationSource));
+                segments.Add(new TypeSegment(declaringType, pathType, navigationSource));
             }
 
             segments.Add(segment);