MediaLibrary: Fixing that removing TitlePart from a type with MediaPart causes the type to be unusable due to an implicit dependency, fixes #6047

src/Orchard.Web/Modules/Orchard.MediaLibrary/Handlers/MediaPartHandler.cs

@@ -1,25 +1,40 @@
 using System;
-using Orchard.ContentManagement.Handlers;
-using Orchard.Data;
-using Orchard.MediaLibrary.Services;
-using Orchard.MediaLibrary.Models;
 using System.IO;
-using Orchard.FileSystems.Media;
+using System.Linq;
 using Orchard.ContentManagement;
+using Orchard.ContentManagement.Handlers;
+using Orchard.ContentManagement.MetaData;
+using Orchard.Core.Title.Models;
+using Orchard.Data;
+using Orchard.FileSystems.Media;
+using Orchard.MediaLibrary.Models;
+using Orchard.MediaLibrary.Services;
 
 namespace Orchard.MediaLibrary.Handlers {
     public class MediaPartHandler : ContentHandler {
         private readonly IMediaLibraryService _mediaLibraryService;
         private readonly IStorageProvider _storageProvider;
+        private readonly IContentDefinitionManager _contentDefinitionManager;
 
         public MediaPartHandler(
             IStorageProvider storageProvider,
             IMediaLibraryService mediaLibraryService,
-            IRepository<MediaPartRecord> repository) {
+            IRepository<MediaPartRecord> repository,
+            IContentDefinitionManager contentDefinitionManager) {
             _storageProvider = storageProvider;
             _mediaLibraryService = mediaLibraryService;
+            _contentDefinitionManager = contentDefinitionManager;
 
             Filters.Add(StorageFilter.For(repository));
+            Filters.Add(new ActivatingFilter<TitlePart>(contentType => {
+                var typeDefinition = _contentDefinitionManager.GetTypeDefinition(contentType);
+                // To avoid NRE when the handler runs for ad-hoc content types, e.g. MediaLibraryExplorer.
+                return typeDefinition == null ?
+                    false :
+                    typeDefinition.Parts.Any(contentTypePartDefinition =>
+                        contentTypePartDefinition.PartDefinition.Name == typeof(MediaPart).Name);
+            }));
+
             OnRemoving<MediaPart>((context, part) => RemoveMedia(part));
             OnLoaded<MediaPart>((context, part) => {
                 if (!String.IsNullOrEmpty(part.FileName)) {

src/Orchard.Web/Modules/Orchard.MediaLibrary/Models/MediaPart.cs

@@ -1,8 +1,10 @@
 using System;
 using Orchard.ContentManagement;
 using Orchard.ContentManagement.FieldStorage.InfosetStorage;
+using Orchard.ContentManagement.Handlers;
 using Orchard.ContentManagement.Utilities;
 using Orchard.Core.Title.Models;
+using Orchard.MediaLibrary.Handlers;
 
 namespace Orchard.MediaLibrary.Models {
     public class MediaPart : ContentPart<MediaPartRecord> {
@@ -11,6 +13,8 @@ namespace Orchard.MediaLibrary.Models {
 
         /// <summary>
         /// Gets or sets the title of the media.
+        /// This adds an implicit dependency on <see cref="TitlePart"/> which will be resolved by an
+        /// <see cref="ActivatingFilter{TPart}"/> in the <see cref="MediaPartHandler"/>.
         /// </summary>
         public string Title {
             get { return ContentItem.As<TitlePart>().Title; }
@@ -63,7 +67,7 @@ namespace Orchard.MediaLibrary.Models {
         /// Gets the public Url of the media if stored locally.
         /// </summary>
         public string MediaUrl {
-            get { return _publicUrl.Value;  }
+            get { return _publicUrl.Value; }
         }
 
         /// <summary>