Introduced new GetRootTopic() extension method

JeremyCaney · JeremyCaney · commit 0bddfb0144f5 · 2020-05-02T18:09:15.000-07:00
Originally, the `OnTopic.Querying` class was focused on querying the current `Topic` and its descendants. Increasingly, however, we're identifying needs to work with the entire in-memory topic graph starting from an arbitrary position within the tree. This is particularly useful when it's difficult or inappropriate to inject an `ITopicRepository` such that we have access from the root.

To start, the `GetRootTopic()` extension now allows us to easily access the root topic of any graph starting from any arbitrary point. It's a really simple recrusive function.

This includes a unit test for validating the functionality.
diff --git a/OnTopic.Tests/TopicQueryingTest.cs b/OnTopic.Tests/TopicQueryingTest.cs
@@ -44,5 +44,25 @@ public void FindAllByAttribute_ReturnsCorrectTopics() {
 
     }
 
+    /*==========================================================================================================================
+    | TEST: GET ROOT TOPIC: RETURNS ROOT TOPIC
+    \-------------------------------------------------------------------------------------------------------------------------*/
+    /// <summary>
+    ///   Given a deeply nested <see cref="Topic"/>, returns the root <see cref="Topic"/>.
+    /// </summary>
+    [TestMethod]
+    public void GetRootTopic_ReturnsRootTopic() {
+
+      var parentTopic           = TopicFactory.Create("ParentTopic", "Page", 1);
+      var childTopic            = TopicFactory.Create("ChildTopic", "Page", 5, parentTopic);
+      var grandChildTopic       = TopicFactory.Create("GrandChildTopic", "Page", 20, childTopic);
+      var greatGrandChildTopic  = TopicFactory.Create("GreatGrandChildTopic", "Page", 7, grandChildTopic);
+
+      var rootTopic             = greatGrandChildTopic.GetRootTopic();
+
+      Assert.ReferenceEquals(parentTopic, rootTopic);
+
+    }
+
   } //Class
 } //Namespace
diff --git a/OnTopic/Querying/TopicExtensions.cs b/OnTopic/Querying/TopicExtensions.cs
@@ -142,5 +142,34 @@ public static ReadOnlyTopicCollection<Topic> FindAllByAttribute(this Topic topic
 
     }
 
+    /*==========================================================================================================================
+    | METHOD: GET ROOT TOPIC
+    \-------------------------------------------------------------------------------------------------------------------------*/
+    /// <summary>
+    ///   Retrieves the root <see cref="Topic"/> in the current topic graph.
+    /// </summary>
+    /// <param name="topic">The instance of the <see cref="Topic"/> to operate against; populated automatically by .NET.</param>
+    /// <returns>The <see cref="Topic"/> at the root o the current topic graph.</returns>
+    public static Topic GetRootTopic(this Topic topic) {
+
+      /*------------------------------------------------------------------------------------------------------------------------
+      | Validate contracts
+      \-----------------------------------------------------------------------------------------------------------------------*/
+      Contract.Requires(topic, "The topic parameter must be specified.");
+
+      /*------------------------------------------------------------------------------------------------------------------------
+      | Find lowest common root
+      \-----------------------------------------------------------------------------------------------------------------------*/
+      while (topic.Parent != null) {
+        topic = topic.Parent;
+      }
+
+      /*------------------------------------------------------------------------------------------------------------------------
+      | Return root
+      \-----------------------------------------------------------------------------------------------------------------------*/
+      return topic;
+
+    }
+
   } //Class
 } //Namespace
