Merge branch 'improvement/TopicMappingService-type-checking' into develop

Introduced a new `GetValidatedMappingType()` method which determines and validates the mapping type against a target type (88c7fba). This method is then integrated with both `PopulateTargetCollectionAsync()` (7caa832) and `GetTopicReferenceAsync()` (a31864a) as a way of pre-validating type compatibility _prior_ to mapping the source topic, thus offering a more efficient way of filtering out incompatible types. Previously, the source topics were first mapped and only then filtered out, thus potentially wasting resources mapping topics that would never be used. This could be especially expensive if the models those topics were being mapped to `[Include()]`d associations. This satisfies the requirements of #83.

Author: JeremyCaney

OnTopic/Mapping/TopicMappingService.cs

@@ -978,13 +978,11 @@ configuration.ContentTypeFilter is not null &&
         }
 
         //Map child topic to target DTO
-        var childDto = (object)childTopic;
+        var childDto            = (object)childTopic;
         if (!typeof(Topic).IsAssignableFrom(listType)) {
-          if (configuration.MapAs != null) {
-            taskQueue.Add(MapAsync(childTopic, configuration.MapAs, configuration.IncludeAssociations, cache));
-          }
-          else {
-            taskQueue.Add(MapAsync(childTopic, configuration.IncludeAssociations, cache));
+          var mappingType       = GetValidatedMappingType(configuration.MapAs, listType)?? GetValidatedMappingType(childTopic, listType);
+          if (mappingType is not null) {
+            taskQueue.Add(MapAsync(childTopic, mappingType, configuration.IncludeAssociations, cache));
           }
         }
         else {
@@ -1009,7 +1007,7 @@ configuration.ContentTypeFilter is not null &&
       | Function: Add to List
       \-----------------------------------------------------------------------------------------------------------------------*/
       void AddToList(object dto) {
-        if (dto is not null && listType.IsAssignableFrom(dto.GetType())) {
+        if (dto is not null) {
           try {
             targetList.Add(dto);
           }
@@ -1022,6 +1020,34 @@ void AddToList(object dto) {
 
     }
 
+    /*==========================================================================================================================
+    | PRIVATE: GET VALIDATED MODEL TYPE
+    \-------------------------------------------------------------------------------------------------------------------------*/
+    /// <summary>
+    ///   Given a <paramref name="sourceTopic"/> <see cref="Topic"/>, identifies the target model type associated with it and
+    ///   validates it against the <paramref name="expectedType"/>.
+    /// </summary>
+    /// <param name="sourceTopic">The source <see cref="Topic"/> that the target type should be inferred from.</param>
+    /// <param name="expectedType">The expected <see cref="Type"/> that the inferred type must be compatible with.</param>
+    /// <returns>The inferred target type, if valid, otherwise null.</returns>
+    private Type? GetValidatedMappingType(Topic sourceTopic, Type expectedType) =>
+      GetValidatedMappingType(
+        _typeLookupService.Lookup($"{sourceTopic.ContentType}TopicViewModel", $"{sourceTopic.ContentType}ViewModel"),
+        expectedType
+      );
+
+    /// <summary>
+    ///   Given a <paramref name="mappingType"/> <see cref="Type"/>, validates it against the <paramref name="expectedType"/>.
+    ///   If it is compatible, returns the <paramref name="mappingType"/>. Otherwise, returns null.
+    /// </summary>
+    /// <param name="mappingType">The source <see cref="Type"/> that should be validated.</param>
+    /// <param name="expectedType">
+    ///   The expected <see cref="Type"/> that the <paramref name="mappingType"/> must be compatible with.
+    /// </param>
+    /// <returns>The <paramref name="mappingType"/>, if valid, otherwise null.</returns>
+    private static Type? GetValidatedMappingType(Type? mappingType, Type expectedType) =>
+      expectedType.IsAssignableFrom(mappingType)? mappingType : null;
+
     /*==========================================================================================================================
     | PRIVATE: GET TOPIC REFERENCE
     \-------------------------------------------------------------------------------------------------------------------------*/
@@ -1059,23 +1085,17 @@ MappedTopicCache cache
       /*------------------------------------------------------------------------------------------------------------------------
       | Map referenced topic
       \-----------------------------------------------------------------------------------------------------------------------*/
-      var topicDto = (object?)null;
-      try {
-        if (configuration.MapAs != null) {
-          topicDto = await MapAsync(source, configuration.MapAs, configuration.IncludeAssociations, cache).ConfigureAwait(false);
-        }
-        else {
-          topicDto = await MapAsync(source, configuration.IncludeAssociations, cache).ConfigureAwait(false);
-        }
-      }
-      catch (InvalidTypeException) {
-        //Disregard errors caused by unmapped view models; those are functionally equivalent to IsAssignableFrom() mismatches
+      var topicDto              = (object?)null;
+      var mappingType           = GetValidatedMappingType(configuration.MapAs, targetType)?? GetValidatedMappingType(source, targetType);
+
+      if (mappingType is not null) {
+        topicDto = await MapAsync(source, mappingType, configuration.IncludeAssociations, cache).ConfigureAwait(false);
       }
 
       /*------------------------------------------------------------------------------------------------------------------------
       | Validate results
       \-----------------------------------------------------------------------------------------------------------------------*/
-      if (topicDto is null || !targetType.IsAssignableFrom(topicDto.GetType())) {
+      if (topicDto is null) {
         return null;
       }
 

OnTopic/Repositories/TopicRepository.cs

@@ -515,7 +515,7 @@ topic.Parent is not null &&
       /*------------------------------------------------------------------------------------------------------------------------
       | Execute core implementation
       \-----------------------------------------------------------------------------------------------------------------------*/
-      if (!topic.IsNew && !target.IsNew && !sibling.IsNew) {
+      if (!topic.IsNew && !target.IsNew && !(sibling?.IsNew?? true)) {
         MoveTopic(topic, target, sibling);
       }