Migrated GetContentTypes(ContentTypeDescriptor) to new Refresh() method

Migrated the `TopicRepositoryBase.GetContentTypes(ContentTypeDescriptor)` overload to utilize the newly introduced `ContentTypeDescriptorCollection.Refresh()` method (3e3930f).

Since the `GetContentTypes()` overload was already migrated, this allows the removal of unintuitive state tracking via the `_contentTypeDescriptors` field initialization in order to avoid a circular loop (since each function previously called into the other). and since `Refresh()` now has the core functionality which this overload was previously dependent on, that can now be removed. Indeed, this greatly simplifies the logic for this overload.

As part of this, the logic also changes so that the source topic graph is always utilized, assuming it can be identified. This is actually faster than trying to merge the two collections via the `Refresh()` method. But, more importantly, it also avoids some complications caused by versioning conflicts between different in-memory representations of `ContentTypeDescriptor`s (e.g., one in `CachedTopicRepository`, another in `SqlTopicRepository`). By replacing the entire collection, we avoid these types of problems, and help ensure that the cache is always using the same topic graph that the application is operating off of.

Author: JeremyCaney

OnTopic/Repositories/TopicRepositoryBase.cs

@@ -107,38 +107,25 @@ public virtual ContentTypeDescriptorCollection GetContentTypeDescriptors() {
     /// <returns></returns>
     protected virtual ContentTypeDescriptorCollection GetContentTypeDescriptors(ContentTypeDescriptor? contentTypeDescriptors) {
 
-      /*------------------------------------------------------------------------------------------------------------------------
-      | Initialize the collection from the repository
-      >-------------------------------------------------------------------------------------------------------------------------
-      | ### NOTE JJC2020519: We want to centralize the shared logic from the public GetContentTypeDescriptors() while still
-      | ensuring the cache is first initialized from the underlying data store if this method is called directly. But we don't
-      | want to repeatedly call the underlying data store if it's empty, nor do we want to create a circular loop if this is
-      | being called from GetContentTypeDescriptors(). This is handled by initializing the _contentTypeDescriptors cache in the
-      | GetContentTypeDescriptors() method as a way of tracking the initialization state.
-      \-----------------------------------------------------------------------------------------------------------------------*/
-      if (_contentTypeDescriptors == null) {
-        _contentTypeDescriptors = GetContentTypeDescriptors();
-      }
 
       /*------------------------------------------------------------------------------------------------------------------------
-      | Validate parameters
+      | Establish cache
+      >-------------------------------------------------------------------------------------------------------------------------
+      | Instead of attempting to merge the source collection with the cached collection, we'll just recreate the cached
+      | collection based on the source collection. This is faster, and helps avoid potential versioning conflicts caused by
+      | mixing objects from different topic graphs. Instead, we always assume that the source collection is the most accurate
+      | and relevant.
       \-----------------------------------------------------------------------------------------------------------------------*/
-      if (contentTypeDescriptors == null) {
-        return _contentTypeDescriptors;
-      }
+      _contentTypeDescriptors.Refresh(contentTypeDescriptors);
 
       /*------------------------------------------------------------------------------------------------------------------------
-      | Add available Content Types to the collection
+      | Validate cache
+      >-------------------------------------------------------------------------------------------------------------------------
+      | If the source cache collection is empty then we'll want to defer to the existing version�or retrieve it from the
+      | persistence layer�via GetContentTypeDescriptors().
       \-----------------------------------------------------------------------------------------------------------------------*/
-      foreach (var topic in contentTypeDescriptors.FindAllByAttribute("ContentType", "ContentType")) {
-        // Ensure the Topic is used as the strongly-typed ContentType
-        // Add ContentType Topic to collection if not already added
-        if (
-          topic is ContentTypeDescriptor contentTypeDescriptor &&
-          !_contentTypeDescriptors.Contains(contentTypeDescriptor.Key)
-        ) {
-          _contentTypeDescriptors.Add(contentTypeDescriptor);
-        }
+      if (_contentTypeDescriptors.Count == 0) {
+        GetContentTypeDescriptors();
       }
 
       /*------------------------------------------------------------------------------------------------------------------------
@@ -184,15 +171,13 @@ topic is ContentTypeDescriptor contentTypeDescriptor &&
       }
 
       /*------------------------------------------------------------------------------------------------------------------------
-      | Retrieve content type
+      | Attempt to update content types from source graph
       \-----------------------------------------------------------------------------------------------------------------------*/
-      if (
-        sourceTopic.GetByUniqueKey("Root:Configuration:ContentTypes") is ContentTypeDescriptor sourceContentTypes &&
-        !contentTypes.Contains(sourceContentTypes)
-      ) {
-        contentTypes            = GetContentTypeDescriptors(sourceContentTypes);
-      }
+      SetContentTypeDescriptors(sourceTopic);
 
+      /*------------------------------------------------------------------------------------------------------------------------
+      | Retrieve content type
+      \-----------------------------------------------------------------------------------------------------------------------*/
       return contentTypes.Contains(contentType)? contentTypes[contentType] : null;
 
     }