Merge branch 'bugfix/TopicListAttributeViewComponent-issues' into develop

Resolves a series of bugs and oversights regarding the implementation of the `TopicListAttributeViewComponent` to ensure all intended functionality is supported, and that it works without error.

This includes:
- Ensure `DefaultLabel` isn't persisted as the value if not topic is selected (1be3eb3)
- Resolve runtime exception when using `RelativeTopicBase`'s `ContentTypeDescriptor` (339fa6d)
- Gracefully fail if the `TopicList`'s scope cannot be resolved (9ecf880)
- Ensure `RelativeTopicBase` works correctly when creating new topics (7f027c6)
- Introduce missing support for the `RelativeTopicPath` attribute (b727cf1)
- Hide the `TopicListViewComponent` if no values are returned (753d0a4)

Author: JeremyCaney

OnTopic.Editor.AspNetCore/Areas/Editor/Views/Editor/Components/TopicList/Default.cshtml

@@ -1,14 +1,18 @@
 @model TopicListAttributeViewModel
 
 @{
+  if (Model.TopicList.Count > 1) {
     Layout = "~/Areas/Editor/Views/Editor/Components/_Layout.cshtml";
+  }
 }
 
-<select
-  asp-for                       ="Value"
-  asp-items                     ="Model.TopicList"
-  class                         ="@Model.AttributeDescriptor.CssClass form-control form-inline"
-  disabled                      =@(!Model.AttributeDescriptor.IsEnabled)
-  required                      =@Model.AttributeDescriptor.IsRequired
-  >
-</select>
+@if (Model.TopicList.Count > 1) {
+  <select
+    asp-for                       ="Value"
+    asp-items                     ="Model.TopicList"
+    class                         ="@Model.AttributeDescriptor.CssClass form-control form-inline"
+    disabled                      =@(!Model.AttributeDescriptor.IsEnabled)
+    required                      =@Model.AttributeDescriptor.IsRequired
+    >
+  </select>
+}

OnTopic.Editor.AspNetCore/Components/TopicListViewComponent.cs

@@ -12,6 +12,7 @@
 using OnTopic.Editor.Models;
 using OnTopic.Editor.Models.Metadata;
 using OnTopic.Editor.Models.Queryable;
+using OnTopic.Querying;
 using OnTopic.Repositories;
 
 namespace OnTopic.Editor.AspNetCore.Components {
@@ -76,7 +77,7 @@ public IViewComponentResult Invoke(
       \-----------------------------------------------------------------------------------------------------------------------*/
       viewModel.TopicList.Add(
         new SelectListItem {
-          Value = null,
+          Value = "",
           Text = attribute.DefaultLabel
         }
       );
@@ -87,35 +88,42 @@ public IViewComponentResult Invoke(
       var defaultValue = currentTopic.Attributes.ContainsKey(attribute.Key)? currentTopic.Attributes[attribute.Key] : null;
 
       /*------------------------------------------------------------------------------------------------------------------------
-      | Get values
+      | Get root topic
       \-----------------------------------------------------------------------------------------------------------------------*/
-      var topics = (List<QueryResultTopicViewModel>)null;
+      var rootTopic             = (Topic)null;
 
       if (attribute.RelativeTopicBase != null) {
         var baseTopic             = _topicRepository.Load(currentTopic.UniqueKey);
-        var rootTopic             = attribute.RelativeTopicBase switch {
+        if (String.IsNullOrEmpty(currentTopic.Key)) {
+          baseTopic               = TopicFactory.Create("NewTopic", currentTopic.ContentType, baseTopic);
+          baseTopic.Parent.Children.Remove(baseTopic);
+        }
+        rootTopic                 = attribute.RelativeTopicBase switch {
           "CurrentTopic"          => baseTopic,
           "ParentTopic"           => baseTopic.Parent,
           "GrandparentTopic"      => (Topic)baseTopic.Parent?.Parent,
-          "ContentTypeDescriptor" => (Topic)_topicRepository.GetContentTypeDescriptors().Where(t => t.Key.Equals(baseTopic.ContentType)),
+          "ContentTypeDescriptor" => (Topic)_topicRepository.GetContentTypeDescriptors().FirstOrDefault(t => t.Key.Equals(baseTopic.ContentType)),
           _ => baseTopic
         };
-        topics = GetTopics(
-          rootTopic,
-          attribute.AttributeKey,
-          attribute.AttributeValue,
-          allowedKeys
-        );
       }
       else {
-        topics = GetTopics(
-          _topicRepository.Load(attribute.RootTopic?.UniqueKey?? attribute.RootTopicKey),
-          attribute.AttributeKey,
-          attribute.AttributeValue,
-          allowedKeys
-        );
+        rootTopic = _topicRepository.Load(attribute.RootTopic?.UniqueKey?? attribute.RootTopicKey);
+      }
+
+      if (rootTopic != null && !String.IsNullOrEmpty(attribute.RelativeTopicPath)) {
+        rootTopic = rootTopic.GetByUniqueKey(rootTopic.GetUniqueKey() + ":" + attribute.RelativeTopicPath);
       }
 
+      /*------------------------------------------------------------------------------------------------------------------------
+      | Get values
+      \-----------------------------------------------------------------------------------------------------------------------*/
+      var topics = GetTopics(
+        rootTopic,
+        attribute.AttributeKey,
+        attribute.AttributeValue,
+        allowedKeys
+      );
+
       /*------------------------------------------------------------------------------------------------------------------------
       | Get values from repository
       \-----------------------------------------------------------------------------------------------------------------------*/
@@ -158,6 +166,13 @@ public static List<QueryResultTopicViewModel> GetTopics(
       string allowedKeys        = ""
     ) {
 
+      /*------------------------------------------------------------------------------------------------------------------------
+      | Swallow missing topic
+      \-----------------------------------------------------------------------------------------------------------------------*/
+      if (topic == null) {
+        return new List<QueryResultTopicViewModel>();
+      }
+
       /*------------------------------------------------------------------------------------------------------------------------
       | Establish query options
       \-----------------------------------------------------------------------------------------------------------------------*/