Introduce new 'DeleteOrphanedLastModifiedAttributes` maintenance procedure

Current versions on the OnTopic Library continue to write new `LastModified` attribute records every time a topic is saved in the OnTopic Editor—_even if no other attributes have been modified_. That's because the `LastModified` date is always different, and thus triggers the OnTopic Library's `IsDirty` check, which otherwise reduces non-changes from being saved. Over time, these values can add clutter to the database, reduce performance of some queries, and introduce a lot of "ghost" versions which don't represent _real_ versions. A future version of the OnTopic Library should develop a smarter way of evaluating these and conditionally saving them. In the meanwhile, however, they persist. As such, the `DeleteOrphanedLastModifiedAttributes` maintenance procedure will identify any orphaned `LastModified` attributes—i.e., ones whose `Version` doesn't map to any other modifications to indexed or extended attributes—and delete them. This can significantly reduce the amount of clutter and overall number of indexed attributes in the `Attributes` table. This may need to be run occassionally to prevent these from reaccumulating.

Author: JeremyCaney

OnTopic.Data.Sql.Database/Maintenance/DeleteOrphanedLastModifiedAttributes.sql

@@ -0,0 +1,55 @@
+--------------------------------------------------------------------------------------------------------------------------------
+-- DELETE ORPHANED LAST MODIFIED ATTRIBUTES
+--------------------------------------------------------------------------------------------------------------------------------
+-- Current versions of the OnTopic Library evaluate whether or not an attribute value has changed since the previous version,
+-- and doesn't create a new attribute version if it has. This process doesn't work for <c>LastModified</c>, however, as that
+-- value changes every time a value is saved—at least via the OnTopic Editor. If you save a topic five times in the editor, it
+-- will generate five <c>LastModified</c> values, <i>even if no other attribute values changed</i>. Over time, this can create a
+-- lot of clutter in the database, and potentially slow down some queries. This script identifies <c>LastModified</c> attributes
+-- which don't correspond to any other updates of <i>indexed</i> attributes, and deletes them.
+--------------------------------------------------------------------------------------------------------------------------------
+-- NOTE: There are legitimate scenarios where a topic is updated but it doesn't show up in other attribute values, such as when
+-- relationships are updated. These situations are the exception, however, and it's usually not an issue to lose that level of
+-- granularity.
+--------------------------------------------------------------------------------------------------------------------------------
+
+CREATE PROCEDURE [dbo].[DeleteOrphanedLastModifiedAttributes]
+AS
+
+SET NOCOUNT ON;
+
+--------------------------------------------------------------------------------------------------------------------------------
+-- CHECK INITIAL VALUES
+--------------------------------------------------------------------------------------------------------------------------------
+DECLARE	@Count	INT
+
+SELECT	@Count	= Count(TopicID)
+FROM	Attributes
+WHERE	AttributeKey	= 'LastModified'
+
+Print('Initial Count: ' + CAST(@Count AS VARCHAR) + ' LastModified records in the database.');
+
+--------------------------------------------------------------------------------------------------------------------------------
+-- DELETE ORPHANED LAST MODIFIED ATTRIBUTES
+--------------------------------------------------------------------------------------------------------------------------------
+DELETE	Attributes
+FROM	Attributes
+LEFT JOIN	Attributes Unmatched
+  ON	Attributes.TopicID = Unmatched.TopicID
+  AND	Attributes.Version = Unmatched.Version
+  AND	Attributes.AttributeKey != Unmatched.AttributeKey
+LEFT JOIN	ExtendedAttributes UnmatchedExtended
+  ON	Attributes.TopicID = UnmatchedExtended.TopicID
+  AND	Attributes.Version = UnmatchedExtended.Version
+WHERE	Unmatched.AttributeKey is null
+  AND	UnmatchedExtended.TopicID is null
+  AND	Attributes.AttributeKey = 'LastModified'
+
+--------------------------------------------------------------------------------------------------------------------------------
+-- CHECK FINAL VALUES
+--------------------------------------------------------------------------------------------------------------------------------
+SELECT	@Count	= @Count - Count(TopicID)
+FROM	Attributes
+WHERE	AttributeKey	= 'LastModified'
+
+Print('Final Count: ' + CAST(@Count AS VARCHAR) + ' orphaned LastModified records were identified and deleted.')

OnTopic.Data.Sql.Database/OnTopic.Data.Sql.Database.sqlproj

@@ -101,6 +101,7 @@
     <Build Include="Types\TopicList.sql" />
     <Build Include="Views\AttributeIndex.sql" />
     <Build Include="Maintenance\DeleteConsecutiveExtendedAttributes.sql" />
+    <Build Include="Maintenance\DeleteOrphanedLastModifiedAttributes.sql" />
     <Build Include="Maintenance\DeleteConsecutiveAttributes.sql" />
   </ItemGroup>
   <ItemGroup>