Introduced IsDirty() method to RelatedTopicCollection

The `IsDirty()` method simply evaluates the `NamedTopicCollection.IsDirty` flag from each child collection (4762694) and returns `true` if _any_ of them are `true`. This allows callers to quickly assess whether or not any relationships have changed.

Author: JeremyCaney

OnTopic.Tests/RelatedTopicCollectionTest.cs

@@ -14,7 +14,7 @@ namespace OnTopic.Tests {
   | CLASS: RELATED TOPIC COLLECTION TEST
   \---------------------------------------------------------------------------------------------------------------------------*/
   /// <summary>
-  ///   Provides unit tests for the <see cref="AttributeValueCollection"/> class.
+  ///   Provides unit tests for the <see cref="RelatedTopicCollection"/> class.
   /// </summary>
   [TestClass]
   public class RelatedTopicCollectionTest {
@@ -37,6 +37,24 @@ public void SetTopic_CreatesRelationship() {
 
     }
 
+    /*==========================================================================================================================
+    | TEST: SET TOPIC: IS DIRTY
+    \-------------------------------------------------------------------------------------------------------------------------*/
+    /// <summary>
+    ///   Sets a relationship and confirms that the <see cref="RelatedTopicCollection.IsDirty"/> returns true.
+    /// </summary>
+    [TestMethod]
+    public void SetTopic_IsDirty() {
+
+      var parent                = TopicFactory.Create("Parent", "Page");
+      var related               = TopicFactory.Create("Related", "Page");
+
+      parent.Relationships.SetTopic("Friends", related);
+
+      Assert.IsTrue(parent.Relationships.IsDirty());
+
+    }
+
     /*==========================================================================================================================
     | TEST: SET TOPIC: CREATES INCOMING RELATIONSHIP
     \-------------------------------------------------------------------------------------------------------------------------*/

OnTopic/Collections/RelatedTopicCollection.cs

@@ -6,6 +6,7 @@
 using System;
 using System.Collections.ObjectModel;
 using System.Linq;
+using System.Xml.Serialization;
 using OnTopic.Internal.Diagnostics;
 
 namespace OnTopic.Collections {
@@ -223,6 +224,15 @@ public void SetTopic(string relationshipKey, Topic topic, bool isIncoming) {
 
     }
 
+    /*==========================================================================================================================
+    | METHOD: IS DIRTY?
+    \-------------------------------------------------------------------------------------------------------------------------*/
+    /// <summary>
+    ///   Evaluates each of the child <see cref="NamedTopicCollection"/>s to determine if any of them are set to <see
+    ///   cref="NamedTopicCollection.IsDirty"/>. If they are, returns <c>true</c>.
+    /// </summary>
+    public bool IsDirty() => Items.Any(r => r.IsDirty);
+
     /*==========================================================================================================================
     | OVERRIDE: INSERT ITEM
     \-------------------------------------------------------------------------------------------------------------------------*/