Avoid file retrieval overhead when detaching BeatmapSetInfo

It seems that no usages of `BeatmapSetInfo` detaches require files - a
`WorkingBeatmap` is always obtained before doing further lookups.

Therefore we can omit this include unless the detaching object is a
`BeatmapInfo`. A refetch is performed when retrieving a
`WorkingBeatmap` to complete the equation.

osu.Game/Beatmaps/BeatmapManager.cs

@@ -299,7 +299,23 @@ namespace osu.Game.Beatmaps
 
         #region Implementation of IWorkingBeatmapCache
 
-        public WorkingBeatmap GetWorkingBeatmap(BeatmapInfo? importedBeatmap) => workingBeatmapCache.GetWorkingBeatmap(importedBeatmap);
+        public WorkingBeatmap GetWorkingBeatmap(BeatmapInfo? importedBeatmap)
+        {
+            // Detached sets don't come with files.
+            // If we seem to be missing files, now is a good time to re-fetch.
+            if (importedBeatmap?.BeatmapSet?.Files.Count == 0)
+            {
+                using (var realm = contextFactory.CreateContext())
+                {
+                    var refetch = realm.Find<BeatmapInfo>(importedBeatmap.ID)?.Detach();
+
+                    if (refetch != null)
+                        importedBeatmap = refetch;
+                }
+            }
+
+            return workingBeatmapCache.GetWorkingBeatmap(importedBeatmap);
+        }
 
         public WorkingBeatmap GetWorkingBeatmap(ILive<BeatmapInfo>? importedBeatmap)
         {

osu.Game/Database/RealmObjectExtensions.cs

@@ -76,6 +76,14 @@ namespace osu.Game.Database
         {
             applyCommonConfiguration(c);
 
+            c.CreateMap<BeatmapSetInfo, BeatmapSetInfo>()
+             .MaxDepth(2)
+             .AfterMap((s, d) =>
+             {
+                 foreach (var beatmap in d.Beatmaps)
+                     beatmap.BeatmapSet = d;
+             });
+
             // This can be further optimised to reduce cyclic retrievals, similar to the optimised set mapper below.
             // Only hasn't been done yet as we detach at the point of BeatmapInfo less often.
             c.CreateMap<BeatmapInfo, BeatmapInfo>()
@@ -100,6 +108,15 @@ namespace osu.Game.Database
         {
             applyCommonConfiguration(c);
 
+            c.CreateMap<BeatmapSetInfo, BeatmapSetInfo>()
+             .MaxDepth(2)
+             .ForMember(b => b.Files, cc => cc.Ignore())
+             .AfterMap((s, d) =>
+             {
+                 foreach (var beatmap in d.Beatmaps)
+                     beatmap.BeatmapSet = d;
+             });
+
             c.CreateMap<BeatmapInfo, BeatmapInfo>()
              .MaxDepth(1)
              .ForMember(b => b.BeatmapSet, cc => cc.Ignore());
@@ -131,13 +148,6 @@ namespace osu.Game.Database
             c.CreateMap<RealmUser, RealmUser>();
             c.CreateMap<RealmFile, RealmFile>();
             c.CreateMap<RealmNamedFileUsage, RealmNamedFileUsage>();
-            c.CreateMap<BeatmapSetInfo, BeatmapSetInfo>()
-             .MaxDepth(2)
-             .AfterMap((s, d) =>
-             {
-                 foreach (var beatmap in d.Beatmaps)
-                     beatmap.BeatmapSet = d;
-             });
         }
 
         /// <summary>