Simplify and document DatabaseStore API

osu.Game.Tests/Beatmaps/IO/ImportBeatmapTest.cs

@@ -115,9 +115,11 @@ namespace osu.Game.Tests.Beatmaps.IO
         {
             IEnumerable<BeatmapSetInfo> resultSets = null;
 
+            var store = osu.Dependencies.Get<BeatmapStore>();
+
             Action waitAction = () =>
             {
-                while (!(resultSets = osu.Dependencies.Get<BeatmapStore>().Database.
+                while (!(resultSets = store.Database.
                     Query<BeatmapSetInfo>().Where(s => s.OnlineBeatmapSetID == 241526)).Any())
                     Thread.Sleep(50);
             };
@@ -134,15 +136,16 @@ namespace osu.Game.Tests.Beatmaps.IO
             //if we don't re-check here, the set will be inserted but the beatmaps won't be present yet.
             waitAction = () =>
             {
-                while ((resultBeatmaps = osu.Dependencies.Get<BeatmapStore>().Database.
+                while ((resultBeatmaps = store.Database.
-                    GetAllWithChildren<BeatmapInfo>(s => s.OnlineBeatmapSetID == 241526 && s.BaseDifficultyID > 0)).Count() != 12)
+                    QueryAndPopulate<BeatmapInfo>(s => s.OnlineBeatmapSetID == 241526 && s.BaseDifficultyID > 0)).Count() != 12)
                     Thread.Sleep(50);
             };
 
             Assert.IsTrue(waitAction.BeginInvoke(null, null).AsyncWaitHandle.WaitOne(timeout),
                 @"Beatmaps did not import to the database in allocated time");
 
-            var set = osu.Dependencies.Get<BeatmapStore>().Database.GetChildren(resultSets.First());
+            var set = resultSets.First();
+            store.Database.Populate(set);
 
             Assert.IsTrue(set.Beatmaps.Count == resultBeatmaps.Count(),
                 $@"Incorrect database beatmap count post-import ({resultBeatmaps.Count()} but should be {set.Beatmaps.Count}).");
@@ -152,16 +155,16 @@ namespace osu.Game.Tests.Beatmaps.IO
 
             Assert.IsTrue(set.Beatmaps.Count > 0);
 
-            var beatmap = osu.Dependencies.Get<BeatmapStore>().GetWorkingBeatmap(set.Beatmaps.First(b => b.RulesetID == 0))?.Beatmap;
+            var beatmap = store.GetWorkingBeatmap(set.Beatmaps.First(b => b.RulesetID == 0))?.Beatmap;
             Assert.IsTrue(beatmap?.HitObjects.Count > 0);
 
-            beatmap = osu.Dependencies.Get<BeatmapStore>().GetWorkingBeatmap(set.Beatmaps.First(b => b.RulesetID == 1))?.Beatmap;
+            beatmap = store.GetWorkingBeatmap(set.Beatmaps.First(b => b.RulesetID == 1))?.Beatmap;
             Assert.IsTrue(beatmap?.HitObjects.Count > 0);
 
-            beatmap = osu.Dependencies.Get<BeatmapStore>().GetWorkingBeatmap(set.Beatmaps.First(b => b.RulesetID == 2))?.Beatmap;
+            beatmap = store.GetWorkingBeatmap(set.Beatmaps.First(b => b.RulesetID == 2))?.Beatmap;
             Assert.IsTrue(beatmap?.HitObjects.Count > 0);
 
-            beatmap = osu.Dependencies.Get<BeatmapStore>().GetWorkingBeatmap(set.Beatmaps.First(b => b.RulesetID == 3))?.Beatmap;
+            beatmap = store.GetWorkingBeatmap(set.Beatmaps.First(b => b.RulesetID == 3))?.Beatmap;
             Assert.IsTrue(beatmap?.HitObjects.Count > 0);
         }
     }

osu.Game/Beatmaps/BeatmapDatabase.cs

@@ -94,7 +94,7 @@ namespace osu.Game.Beatmaps
 
         private void cleanupPendingDeletions()
         {
-            foreach (var b in GetAllWithChildren<BeatmapSetInfo>(b => b.DeletePending && !b.Protected))
+            foreach (var b in QueryAndPopulate<BeatmapSetInfo>(b => b.DeletePending && !b.Protected))
             {
                 try
                 {

osu.Game/Beatmaps/BeatmapStore.cs

@@ -150,9 +150,7 @@ namespace osu.Game.Beatmaps
             if (beatmapInfo == null || beatmapInfo == DefaultBeatmap?.BeatmapInfo)
                 return DefaultBeatmap;
 
-            beatmapInfo = Database.GetChildren(beatmapInfo, true);
+            Database.Populate(beatmapInfo);
-
-            Database.GetChildren(beatmapInfo.BeatmapSet, true);
 
             if (beatmapInfo.BeatmapSet == null)
                 throw new InvalidOperationException($@"Beatmap set {beatmapInfo.BeatmapSetInfoID} is not in the local database.");
@@ -185,7 +183,7 @@ namespace osu.Game.Beatmaps
             BeatmapSetInfo set = Database.Query<BeatmapSetInfo>().FirstOrDefault(query);
 
             if (set != null)
-                Database.GetChildren(set, true);
+                Database.Populate(set);
 
             return set;
         }
@@ -235,7 +233,7 @@ namespace osu.Game.Beatmaps
 
             if (existing != null)
             {
-                Database.GetChildren(existing);
+                Database.Populate(existing);
                 Undelete(existing);
                 return existing;
             }

osu.Game/Database/DatabaseStore.cs

@@ -3,6 +3,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Linq;
 using System.Linq.Expressions;
 using osu.Framework.Logging;
 using osu.Framework.Platform;
@@ -42,28 +43,50 @@ namespace osu.Game.Database
         /// </summary>
         public void Reset() => Prepare(true);
 
-        public TableQuery<T> Query<T>() where T : class
+
+        public TableQuery<T> Query<T>(Expression<Func<T, bool>> filter = null) where T : class
         {
-            return Connection.Table<T>();
+            checkType(typeof(T));
+
+            var query = Connection.Table<T>();
+
+            if (filter != null)
+                query = query.Where(filter);
+
+            return query;
         }
 
         /// <summary>
-        /// This is expensive. Use with caution.
+        /// Query and populate results.
         /// </summary>
-        public List<T> GetAllWithChildren<T>(Expression<Func<T, bool>> filter = null, bool recursive = true)
+        /// <param name="filter">An optional filter to refine results.</param>
+        /// <returns></returns>
+        public List<T> QueryAndPopulate<T>(Expression<Func<T, bool>> filter = null)
             where T : class
         {
-            return Connection.GetAllWithChildren(filter, recursive);
+            checkType(typeof(T));
+
+            return Connection.GetAllWithChildren(filter, true);
         }
 
-        public T GetChildren<T>(T item, bool recursive = false)
+        /// <summary>
+        /// Populate a database-backed item.
+        /// </summary>
+        /// <param name="item"></param>
+        /// <param name="recursive">Whether population should recurse beyond a single level.</param>
+        public void Populate<T>(T item, bool recursive = true)
         {
-            if (item == null) return default(T);
+            checkType(item.GetType());
 
             Connection.GetChildren(item, recursive);
-            return item;
+        }
+
+        private void checkType(Type type)
+        {
+            if (!ValidTypes.Contains(type))
+                throw new InvalidOperationException($"The requested operation specified a type of {type}, which is invalid for this {nameof(DatabaseStore)}.");
         }
 
         protected abstract Type[] ValidTypes { get; }
     }
-}
+}

osu.Game/IO/FileDatabase.cs

@@ -97,7 +97,7 @@ namespace osu.Game.IO
 
         private void deletePending()
         {
-            foreach (var f in GetAllWithChildren<FileInfo>(f => f.ReferenceCount < 1))
+            foreach (var f in QueryAndPopulate<FileInfo>(f => f.ReferenceCount < 1))
             {
                 try
                 {

osu.Game/Overlays/Music/PlaylistOverlay.cs

@@ -77,7 +77,7 @@ namespace osu.Game.Overlays.Music
                 },
             };
 
-            list.BeatmapSets = BeatmapSets = beatmaps.Database.GetAllWithChildren<BeatmapSetInfo>(b => !b.DeletePending).ToList();
+            list.BeatmapSets = BeatmapSets = beatmaps.Database.QueryAndPopulate<BeatmapSetInfo>(b => !b.DeletePending).ToList();
 
             beatmaps.BeatmapSetAdded += s => list.AddBeatmapSet(s);
             beatmaps.BeatmapSetRemoved += s => list.RemoveBeatmapSet(s);

osu.Game/Screens/Menu/Intro.cs

@@ -76,10 +76,13 @@ namespace osu.Game.Screens.Menu
 
             if (!menuMusic)
             {
-                var query = beatmaps.Database.Query<BeatmapSetInfo>().Where(b => !b.DeletePending);
+                var query = beatmaps.Database.Query<BeatmapSetInfo>(b => !b.DeletePending);
                 int count = query.Count();
                 if (count > 0)
+                {
                     setInfo = query.ElementAt(RNG.Next(0, count - 1));
+                    beatmaps.Database.Populate(setInfo);
+                }
             }
 
             if (setInfo == null)

osu.Game/Screens/Select/SongSelect.cs

@@ -180,7 +180,7 @@ namespace osu.Game.Screens.Select
 
             initialAddSetsTask = new CancellationTokenSource();
 
-            carousel.Beatmaps = store.Database.GetAllWithChildren<BeatmapSetInfo>(b => !b.DeletePending);
+            carousel.Beatmaps = store.Database.QueryAndPopulate<BeatmapSetInfo>(b => !b.DeletePending);
 
             Beatmap.ValueChanged += beatmap_ValueChanged;