save music brainz id in xml

MediaBrowser.Controller/Entities/Folder.cs

@@ -864,14 +864,7 @@ namespace MediaBrowser.Controller.Entities
         /// <returns>IEnumerable{BaseItem}.</returns>
         protected IEnumerable<BaseItem> GetCachedChildren()
         {
-            var items = ItemRepository.GetChildren(Id).Select(RetrieveChild).Where(i => i != null).ToList();
-
-            foreach (var item in items)
-            {
-                item.Parent = this;
-            }
-
-            return items;
+            return ItemRepository.GetChildren(Id).Select(RetrieveChild).Where(i => i != null);
         }
 
         /// <summary>
@@ -893,7 +886,13 @@ namespace MediaBrowser.Controller.Entities
 
             var item = LibraryManager.RetrieveItem(child.ItemId, itemType);
 
-            return item is IByReferenceItem ? LibraryManager.GetOrAddByReferenceItem(item) : item;
+            if (item is IByReferenceItem)
+            {
+                return LibraryManager.GetOrAddByReferenceItem(item);
+            }
+
+            item.Parent = this;
+            return item;
         }
 
         /// <summary>

MediaBrowser.Controller/Providers/BaseItemXmlParser.cs

@@ -417,6 +417,22 @@ namespace MediaBrowser.Controller.Providers
                         break;
                     }
 
+                case "MusicbrainzId":
+                    var mbz = reader.ReadElementContentAsString();
+                    if (!string.IsNullOrWhiteSpace(mbz))
+                    {
+                        item.SetProviderId(MetadataProviders.Musicbrainz, mbz);
+                    }
+                    break;
+
+                case "RottenTomatoesId":
+                    var rtId = reader.ReadElementContentAsString();
+                    if (!string.IsNullOrWhiteSpace(rtId))
+                    {
+                        item.SetProviderId(MetadataProviders.RottenTomatoes, rtId);
+                    }
+                    break;
+
                 case "TMDbId":
                     var tmdb = reader.ReadElementContentAsString();
                     if (!string.IsNullOrWhiteSpace(tmdb))
@@ -424,7 +440,7 @@ namespace MediaBrowser.Controller.Providers
                         item.SetProviderId(MetadataProviders.Tmdb, tmdb);
                     }
                     break;
-
+                
                 case "CollectionNumber":
                     var tmdbCollection = reader.ReadElementContentAsString();
                     if (!string.IsNullOrWhiteSpace(tmdbCollection))