Fixes up issues when tracking dirty changes on numerical or empty string values because json.net converts numerical to long and we were setting those values on the Property.Value which means that comparing long -> int will always return false and thus the property is flagged as dirty. Same goes with string and null when dealing with an object. This is all fixed up now and have added another method to see if we shold actually persist any changes for content when saving. This all relates to fixing: U4-5510 Previewing a content item saves that item

src/Umbraco.Core/Models/ContentExtensions.cs

@@ -42,6 +42,61 @@ namespace Umbraco.Core.Models
             return dirty.WasPropertyDirty("Published") && entity.Published;
         }
 
+        /// <summary>
+        /// Determines if the item should be persisted at all
+        /// </summary>
+        /// <param name="entity"></param>
+        /// <returns></returns>
+        /// <remarks>
+        /// In one particular case, a content item shouldn't be persisted:
+        /// * The item exists and is published
+        /// * A call to ContentService.Save is made
+        /// * The item has not been modified whatsoever apart from changing it's published status from published to saved
+        /// 
+        /// In this case, there is no reason to make any database changes at all
+        /// </remarks>
+        internal static bool RequiresSaving(this IContent entity)
+        {
+            var publishedState = ((Content)entity).PublishedState;
+            return RequiresSaving(entity, publishedState);
+        }
+
+        /// <summary>
+        /// Determines if the item should be persisted at all
+        /// </summary>
+        /// <param name="entity"></param>
+        /// <param name="publishedState"></param>
+        /// <returns></returns>
+        /// <remarks>
+        /// In one particular case, a content item shouldn't be persisted:
+        /// * The item exists and is published
+        /// * A call to ContentService.Save is made
+        /// * The item has not been modified whatsoever apart from changing it's published status from published to saved
+        /// 
+        /// In this case, there is no reason to make any database changes at all
+        /// </remarks>
+        internal static bool RequiresSaving(this IContent entity, PublishedState publishedState)
+        {
+            var dirtyEntity = (ICanBeDirty)entity;
+            var publishedChanged = dirtyEntity.IsPropertyDirty("Published") && publishedState != PublishedState.Unpublished;
+            //check if any user prop has changed
+            var propertyValueChanged = ((Content)entity).IsAnyUserPropertyDirty();
+            
+            //We need to know if any other property apart from Published was changed here
+            //don't create a new version if the published state has changed to 'Save' but no data has actually been changed
+            if (publishedChanged && entity.Published == false && propertyValueChanged == false)
+            {
+                //at this point we need to check if any non property value has changed that wasn't the published state
+                var changedProps = ((TracksChangesEntityBase)entity).GetDirtyProperties();
+                if (changedProps.Any(x => x != "Published") == false)
+                {
+                    return false;
+                }
+            }
+
+            return true;
+        }
+
         /// <summary>
         /// Determines if a new version should be created
         /// </summary>
@@ -76,9 +131,12 @@ namespace Umbraco.Core.Models
             var dirtyEntity = (ICanBeDirty)entity;
 
             //check if the published state has changed or the language
-            var contentChanged =
-                (dirtyEntity.IsPropertyDirty("Published") && publishedState != PublishedState.Unpublished)
-                || dirtyEntity.IsPropertyDirty("Language");
+            var publishedChanged = dirtyEntity.IsPropertyDirty("Published") && publishedState != PublishedState.Unpublished;
+            var langChanged = dirtyEntity.IsPropertyDirty("Language");
+            var contentChanged = publishedChanged || langChanged;
+
+            //check if any user prop has changed
+            var propertyValueChanged = ((Content)entity).IsAnyUserPropertyDirty();            
 
             //return true if published or language has changed
             if (contentChanged)
@@ -86,8 +144,6 @@ namespace Umbraco.Core.Models
                 return true;
             }
 
-            //check if any user prop has changed
-            var propertyValueChanged = ((Content)entity).IsAnyUserPropertyDirty();
             //check if any content prop has changed
             var contentDataChanged = ((Content)entity).IsEntityDirty();
 
@@ -134,7 +190,7 @@ namespace Umbraco.Core.Models
 
             //If Published state has changed then previous versions should have their publish state reset.
             //If state has been changed to unpublished the previous versions publish state should also be reset.
-            if (((ICanBeDirty)entity).IsPropertyDirty("Published") && (entity.Published || publishedState == PublishedState.Unpublished))
+            if (entity.IsPropertyDirty("Published") && (entity.Published || publishedState == PublishedState.Unpublished))
             {
                 return true;
             }