Introduced new GetContentTypeDescriptors() overload

Previously, the `GetContentTypeDescriptors()` method _exclusively_ relied on retrieving the content type descriptors from the underlying data storage of the concrete implementation. This makes good sense in most read-optimized scenarios, where the metadata schema is well-established.

This introduces problems, however, when trying to persist large, in-memory topic graphs to the storage medium. In those cases, we may need to dynamically update the `GetContentTypeDescriptors()` cache with as-of-yet-unsaved `ContentTypeDescriptor`s in order to bootstrap the database. For example, imagine trying to save the `Root` topic (a `Container` content type) before the `Container` content type descriptor has been persisted to the database.

While this update doesn't support that functionality, it lays the groundwork by allowing implementers to pass an in-memory `ContentTypeDescriptor` to the `GetContentTypeDescriptors()` and either a) use that _instead_ of the data source (potentially useful for bootstrapping the database), or b) merge new `ContentTypeDesciptor`s with the existing cached data (potentially useful when importing large changes, as needed for the **OnTopic Data Exchange** library).

The logic for this largely repeats the existing logic for `GetContentTypeDescriptors()`, so its been modified to load the topic graph from the underlying data source, and then pass it to this new overload as to keep that logic centralized. In this way, this overload maintains existing functionality, while providing additional flexibility for implementers.

This will also lay the groundwork for the newly proposed features:

- Update content type cache when adding or removing content types (#16),
- Update attribute descriptors when adding or removing an attribute (#17), and
- Discover in-memory `ContentTypeDescriptor`, `AttributeDescriptor` on `Save()` (#18).

Includes a unit test to validate the ability to merge new in-memory `ContentTypeDescriptor`s into the `GetContentTypeDescriptors()` cache.

Author: JeremyCaney

OnTopic.TestDoubles/StubTopicRepository.cs

@@ -177,6 +177,13 @@ public IEnumerable<AttributeValue> GetAttributesProxy(Topic topic, bool? isExten
     /// <inheritdoc cref="TopicRepositoryBase.GetUnmatchedAttributes(Topic)" />
     public IEnumerable<AttributeDescriptor> GetUnmatchedAttributesProxy(Topic topic) => base.GetUnmatchedAttributes(topic);
 
+    /*==========================================================================================================================
+    | METHOD: GET CONTENT TYPE DESCRIPTORS (PROXY)
+    \-------------------------------------------------------------------------------------------------------------------------*/
+    /// <inheritdoc cref="TopicRepositoryBase.GetContentTypeDescriptors(ContentTypeDescriptor)" />
+    public ContentTypeDescriptorCollection GetContentTypeDescriptorsProxy(ContentTypeDescriptor topicGraph) =>
+      base.GetContentTypeDescriptors(topicGraph);
+
     /*==========================================================================================================================
     | METHOD: CREATE FAKE DATA
     \-------------------------------------------------------------------------------------------------------------------------*/

OnTopic.Tests/TopicRepositoryBaseTest.cs

@@ -146,5 +146,27 @@ public void GetContentTypeDescriptors_ReturnsContentTypes() {
 
     }
 
+    /*==========================================================================================================================
+    | TEST: GET CONTENT TYPE DESCRIPTORS: WITH TOPIC GRAPH: RETURNS MERGED CONTENT TYPES
+    \-------------------------------------------------------------------------------------------------------------------------*/
+    /// <summary>
+    ///   Retrieves a list of <see cref="ContentTypeDescriptor"/>s from the <see cref="ITopicRepository"/> alongside a separate
+    ///   topic graph and ensures the two are properly merged.
+    /// </summary>
+    [TestMethod]
+    public void GetContentTypeDescriptors_WithTopicGraph_ReturnsMergedContentTypes() {
+
+      var contentTypes          = _topicRepository.GetContentTypeDescriptors();
+      var rootContentType       = contentTypes["ContentTypes"];
+      var newContentType        = TopicFactory.Create("NewContentType", "ContentTypeDescriptor", rootContentType);
+      var contentTypeCount      = contentTypes.Count;
+
+      _topicRepository.GetContentTypeDescriptorsProxy((ContentTypeDescriptor)newContentType);
+
+      Assert.AreNotEqual<int>(contentTypeCount, contentTypes.Count);
+      Assert.IsNotNull(contentTypes.Contains(newContentType));
+
+    }
+
   } //Class
 } //Namespace

OnTopic/Repositories/TopicRepositoryBase.cs

@@ -14,6 +14,7 @@
 using System.Collections.Generic;
 using System.Linq;
 using OnTopic.Collections;
+using OnTopic.Metadata.AttributeTypes;
 
 #pragma warning disable CS0618 // Type or member is obsolete; used to hide known deprecation of events until v5.0.0
 
@@ -66,33 +67,74 @@ public virtual ContentTypeDescriptorCollection GetContentTypeDescriptors() {
         Contract.Assume(configuration, $"The 'Root:Configuration' section could not be loaded from the 'ITopicRepository'.");
 
         /*----------------------------------------------------------------------------------------------------------------------
-        | Add available Content Types to the collection
-        \---------------------------------------------------------------------------------------------------------------------*/
-        _contentTypeDescriptors = new ContentTypeDescriptorCollection();
-
-        /*----------------------------------------------------------------------------------------------------------------------
-        | Ensure the parent ContentTypes topic is available to iterate over
+        | Load root content type
         \---------------------------------------------------------------------------------------------------------------------*/
-        var allowedContentTypes = configuration.Children.GetTopic("ContentTypes");
+        var allowedContentTypes = configuration.Children.GetTopic("ContentTypes") as ContentTypeDescriptor;
 
         Contract.Assume(allowedContentTypes, "Unable to load section 'Configuration:ContentTypes'.");
 
         /*----------------------------------------------------------------------------------------------------------------------
         | Add available Content Types to the collection
         \---------------------------------------------------------------------------------------------------------------------*/
-        foreach (var topic in allowedContentTypes.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);
-          }
-        }
+        _contentTypeDescriptors = GetContentTypeDescriptors(allowedContentTypes);
+
+      }
+
+      return _contentTypeDescriptors;
+
+    }
+
+    /// <summary>
+    ///   Optional overload of <see cref="GetContentTypeDescriptors()"/> allows for a new topic graph to be supplied for
+    ///   updating the list of cached <see cref="ContentTypeDescriptor"/>s.
+    /// </summary>
+    /// <remarks>
+    ///   By default, the <see cref="GetContentTypeDescriptors()"/> method will load data from the concrete implementation of
+    ///   the <see cref="ITopicRepository"/>'s data store. There are cases, however, where it may be preferrable to instead load
+    ///   these topics from a local, in-memory source. Namely, when first instantiating a new OnTopic database, and when saving
+    ///   modifications to existing content types. As such, this <c>protected</c> overload is useful to call from <see
+    ///   cref="ITopicRepository.Save(Topic, Boolean, Boolean)"/> when the topic graph being saved includes any <see
+    ///   cref="ContentTypeDescriptor"/>s.
+    /// </remarks>
+    /// <param name="contentTypeDescriptors">
+    ///   The root of a <see cref="ContentTypeDescriptor"/> topic graph to merge into the collection for <see
+    ///   cref="GetContentTypeDescriptors()"/>. The code will process not only the root <see cref="ContentTypeDescriptor"/>, but
+    ///   also any descendents.
+    /// </param>
+    /// <returns></returns>
+    protected virtual ContentTypeDescriptorCollection GetContentTypeDescriptors(ContentTypeDescriptor contentTypeDescriptors) {
+
+      /*------------------------------------------------------------------------------------------------------------------------
+      | Initialize the collection
+      \-----------------------------------------------------------------------------------------------------------------------*/
+      if (_contentTypeDescriptors == null) {
+        _contentTypeDescriptors = new ContentTypeDescriptorCollection();
+      }
 
+      /*------------------------------------------------------------------------------------------------------------------------
+      | Validate parameters
+      \-----------------------------------------------------------------------------------------------------------------------*/
+      if (contentTypeDescriptors == null) {
+        return _contentTypeDescriptors;
       }
 
+      /*------------------------------------------------------------------------------------------------------------------------
+      | Add available Content Types to the collection
+      \-----------------------------------------------------------------------------------------------------------------------*/
+      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);
+        }
+      }
+
+      /*------------------------------------------------------------------------------------------------------------------------
+      | Add available Content Types to the collection
+      \-----------------------------------------------------------------------------------------------------------------------*/
       return _contentTypeDescriptors;
 
     }