Introduce (optional, default) support for DeleteUnmatched

Currently, in order to delete existing relationships, callers must trigger `UpdateTopic`'s `@DeleteRelationships` flag—which will delete all relationships for that topic—and _then_ call `UpdateRelationship` with the final relationships set. This is wasteful, as often times the relationships will have overlap, or even be identical.

The previous update (e725077) allows doing inserts without recreating existing relationships. This update allows unmatched records to be deleted, thus providing true synchronization with `@RelatedTopics`, without needing to first delete the relationships, nor needing to recreate any relationships.

Optionally, this can be disabled by setting the `@DeletedUnmatched` parameter to `0`, thus only appending any new relationships—though, by default, it is enabled (`1`).

Author: JeremyCaney

OnTopic.Data.Sql.Database/Stored Procedures/UpdateRelationships.sql

@@ -7,7 +7,8 @@
 CREATE PROCEDURE [dbo].[UpdateRelationships]
 	@TopicID		INT	= -1,
 	@RelationshipKey	VARCHAR(255)	= 'related',
-	@RelatedTopics		TopicList	READONLY
+	@RelatedTopics		TopicList	READONLY,
+	@DeleteUnmatched	BIT	= 1
 AS
 
 --------------------------------------------------------------------------------------------------------------------------------
@@ -28,6 +29,19 @@ LEFT JOIN	Relationships		Existing
   AND	Source_TopicID		= @TopicID
 WHERE	Target_TopicID		IS NULL
 
+--------------------------------------------------------------------------------------------------------------------------------
+-- DELETE UNMATCHED VALUES
+--------------------------------------------------------------------------------------------------------------------------------
+IF @DeleteUnmatched = 1
+  BEGIN
+    DELETE	EXISTING
+    FROM	@RelatedTopics		Relationships
+    RIGHT JOIN	Relationships		Existing
+      ON	Target_TopicID		= TopicId
+    WHERE	Source_TopicID		= @TopicID
+      AND	ISNULL(TopicID, '')	= ''
+  END
+
 --------------------------------------------------------------------------------------------------------------------------------
 -- RETURN TOPIC ID
 --------------------------------------------------------------------------------------------------------------------------------