Add the ability to create migrations on a per-store level

Now stores store versions to the database itself.

osu.Game/Beatmaps/BeatmapStore.cs

@@ -17,6 +17,12 @@ namespace osu.Game.Beatmaps
         public event Action<BeatmapSetInfo> BeatmapSetAdded;
         public event Action<BeatmapSetInfo> BeatmapSetRemoved;
 
+        /// <summary>
+        /// The current version of this store. Used for migrations (see <see cref="PerformMigration(int, int)"/>).
+        /// The initial version is 1.
+        /// </summary>
+        protected override int StoreVersion => 1;
+
         public BeatmapStore(SQLiteConnection connection)
             : base(connection)
         {
@@ -50,6 +56,33 @@ namespace osu.Game.Beatmaps
             cleanupPendingDeletions();
         }
 
+        /// <summary>
+        /// Perform migrations between two store versions.
+        /// </summary>
+        /// <param name="currentVersion">The current store version. This will be zero on a fresh database initialisation.</param>
+        /// <param name="newVersion">The target version which we are migrating to (equal to the current <see cref="StoreVersion"/>).</param>
+        protected override void PerformMigration(int currentVersion, int newVersion)
+        {
+            base.PerformMigration(currentVersion, newVersion);
+
+            while (currentVersion++ < newVersion)
+            {
+                switch (currentVersion)
+                {
+                    case 1:
+                        // initialising from a version before we had versioning (or a fresh install).
+
+                        // force adding of Protected column (not automatically migrated).
+                        Connection.MigrateTable<BeatmapSetInfo>();
+
+                        // remove all existing beatmaps.
+                        foreach (var b in Connection.GetAllWithChildren<BeatmapSetInfo>(null, true))
+                            Connection.Delete(b, true);
+                        break;
+                }
+            }
+        }
+
         /// <summary>
         /// Add a <see cref="BeatmapSetInfo"/> to the database.
         /// </summary>

osu.Game/Database/DatabaseBackedStore.cs

@@ -17,6 +17,8 @@ namespace osu.Game.Database
         protected readonly Storage Storage;
         protected readonly SQLiteConnection Connection;
 
+        protected virtual int StoreVersion => 1;
+
         protected DatabaseBackedStore(SQLiteConnection connection, Storage storage = null)
         {
             Storage = storage;
@@ -31,6 +33,28 @@ namespace osu.Game.Database
                 Logger.Error(e, $@"Failed to initialise the {GetType()}! Trying again with a clean database...");
                 Prepare(true);
             }
+
+            checkMigrations();
+        }
+
+        private void checkMigrations()
+        {
+            var storeName = GetType().Name;
+
+            var reportedVersion = Connection.Table<StoreVersion>().FirstOrDefault(s => s.StoreName == storeName) ?? new StoreVersion
+            {
+                StoreName = storeName,
+                Version = 0
+            };
+
+            if (reportedVersion.Version != StoreVersion)
+                PerformMigration(reportedVersion.Version, reportedVersion.Version = StoreVersion);
+
+            Connection.InsertOrReplace(reportedVersion);
+        }
+
+        protected virtual void PerformMigration(int currentVersion, int newVersion)
+        {
         }
 
         /// <summary>

osu.Game/Database/StoreVersion.cs

@@ -0,0 +1,15 @@
+// Copyright (c) 2007-2017 ppy Pty Ltd <contact@ppy.sh>.
+// Licensed under the MIT Licence - https://raw.githubusercontent.com/ppy/osu/master/LICENCE
+
+using SQLite.Net.Attributes;
+
+namespace osu.Game.Database
+{
+    public class StoreVersion
+    {
+        [PrimaryKey]
+        public string StoreName { get; set; }
+
+        public int Version { get; set; }
+    }
+}

osu.Game/OsuGameBase.cs

@@ -18,6 +18,7 @@ using osu.Game.Graphics.Processing;
 using osu.Game.Online.API;
 using SQLite.Net;
 using osu.Framework.Graphics.Performance;
+using osu.Game.Database;
 using osu.Game.IO;
 using osu.Game.Rulesets;
 using osu.Game.Rulesets.Scoring;
@@ -97,6 +98,8 @@ namespace osu.Game
 
             SQLiteConnection connection = Host.Storage.GetDatabase(@"client");
 
+            connection.CreateTable<StoreVersion>();
+
             dependencies.Cache(RulesetStore = new RulesetStore(connection));
             dependencies.Cache(FileStore = new FileStore(connection, Host.Storage));
             dependencies.Cache(BeatmapManager = new BeatmapManager(Host.Storage, FileStore, connection, RulesetStore, Host));

osu.Game/osu.Game.csproj

@@ -80,6 +80,7 @@
     <Compile Include="Beatmaps\DifficultyCalculator.cs" />
     <Compile Include="Beatmaps\DummyWorkingBeatmap.cs" />
     <Compile Include="Beatmaps\IO\LegacyFilesystemReader.cs" />
+    <Compile Include="Database\StoreVersion.cs" />
     <Compile Include="Graphics\Containers\OsuClickableContainer.cs" />
     <Compile Include="Graphics\Containers\OsuFocusedOverlayContainer.cs" />
     <Compile Include="Graphics\Containers\OsuScrollContainer.cs" />