Index: src/MTXSQLite3Storage.m
==================================================================
--- src/MTXSQLite3Storage.m
+++ src/MTXSQLite3Storage.m
@@ -26,10 +26,13 @@
 
 @implementation MTXSQLite3Storage
 {
 	SL3Connection *_conn;
 	SL3PreparedStatement *_nextBatchSetStatement, *_nextBatchGetStatement;
+	SL3PreparedStatement *_joinedRoomsAddStatement;
+	SL3PreparedStatement *_joinedRoomsRemoveStatement;
+	SL3PreparedStatement *_joinedRoomsGetStatement;
 }
 
 + (instancetype)storageWithPath: (OFString *)path
 {
 	return [[[self alloc] initWithPath: path] autorelease];
@@ -53,10 +56,22 @@
 		    @"    $device_id, $next_batch\n"
 		    @")"] retain];
 		_nextBatchGetStatement = [[_conn prepareStatement:
 		    @"SELECT next_batch FROM next_batch\n"
 		    @"WHERE device_id=$device_id"] retain];
+		_joinedRoomsAddStatement = [[_conn prepareStatement:
+		    @"INSERT INTO joined_rooms (\n"
+		    @"    user_id, room_id\n"
+		    @") VALUES (\n"
+		    @"    $user_id, $room_id\n"
+		    @")"] retain];
+		_joinedRoomsRemoveStatement = [[_conn prepareStatement:
+		    @"DELETE FROM joined_rooms\n"
+		    @"WHERE user_id=$user_id AND room_id=$room_id"] retain];
+		_joinedRoomsGetStatement = [[_conn prepareStatement:
+		    @"SELECT room_id FROM joined_rooms\n"
+		    @"WHERE user_id=$user_id"] retain];
 
 		objc_autoreleasePoolPop(pool);
 	} @catch (id e) {
 		[self release];
 		@throw e;
@@ -67,21 +82,30 @@
 
 - (void)dealloc
 {
 	[_nextBatchSetStatement release];
 	[_nextBatchGetStatement release];
+	[_joinedRoomsAddStatement release];
+	[_joinedRoomsRemoveStatement release];
+	[_joinedRoomsGetStatement release];
 	[_conn release];
 
 	[super dealloc];
 }
 
 - (void)createTables
 {
-	[_conn executeStatement: @"CREATE TABLE IF NOT EXISTS next_batch (\n"
-				 @"    device_id TEXT PRIMARY KEY,\n"
-				 @"    next_batch TEXT\n"
-				 @")"];
+	[_conn executeStatement:
+	    @"CREATE TABLE IF NOT EXISTS next_batch (\n"
+	    @"    device_id TEXT PRIMARY KEY,\n"
+	    @"    next_batch TEXT\n"
+	    @");\n"
+	    @"CREATE TABLE IF NOT EXISTS joined_rooms (\n"
+	    @"    user_id TEXT,\n"
+	    @"    room_id TEXT,\n"
+	    @"    PRIMARY KEY (user_id, room_id)\n"
+	    @");"];
 }
 
 - (void)transactionWithBlock: (mtx_storage_transaction_block_t)block
 {
 	[_conn transactionWithBlock: block];
@@ -113,12 +137,61 @@
 
 	if (![_nextBatchGetStatement step])
 		return nil;
 
 	OFString *nextBatch =
-	    [[_nextBatchGetStatement rowDictionary][@"next_batch"] retain];
+	    [_nextBatchGetStatement.rowDictionary[@"next_batch"] retain];
 
 	objc_autoreleasePoolPop(pool);
 
 	return [nextBatch autorelease];
 }
+
+- (void)addJoinedRoom: (OFString *)roomID
+	      forUser: (OFString *)userID
+{
+	void *pool = objc_autoreleasePoolPush();
+
+	[_joinedRoomsAddStatement reset];
+	[_joinedRoomsAddStatement bindWithDictionary: @{
+		@"$room_id": roomID,
+		@"$user_id": userID
+	}];
+	[_joinedRoomsAddStatement step];
+
+	objc_autoreleasePoolPop(pool);
+}
+
+- (void)removeJoinedRoom: (OFString *)roomID
+		 forUser: (OFString *)userID
+{
+	void *pool = objc_autoreleasePoolPush();
+
+	[_joinedRoomsRemoveStatement reset];
+	[_joinedRoomsRemoveStatement bindWithDictionary: @{
+		@"$room_id": roomID,
+		@"$user_id": userID
+	}];
+	[_joinedRoomsRemoveStatement step];
+
+	objc_autoreleasePoolPop(pool);
+}
+
+- (OFArray<OFString *> *)joinedRoomsForUser: (OFString *)userID
+{
+	OFMutableArray *joinedRooms = [OFMutableArray array];
+	void *pool = objc_autoreleasePoolPush();
+
+	[_joinedRoomsGetStatement reset];
+	[_joinedRoomsGetStatement bindWithDictionary: @{
+		@"$user_id": userID
+	}];
+
+	while ([_joinedRoomsGetStatement step])
+		[joinedRooms addObject:
+		    _joinedRoomsGetStatement.rowDictionary[@"room_id"]];
+
+	objc_autoreleasePoolPop(pool);
+
+	return [joinedRooms autorelease];
+}
 @end

Index: src/MTXStorage.h
==================================================================
--- src/MTXStorage.h
+++ src/MTXStorage.h
@@ -56,8 +56,36 @@
  * @param deviceID The device ID for which to return the next batch
  * @return The next batch for the specified device, or `nil` if none is
  *	   available.
  */
 - (nullable OFString *)nextBatchForDeviceID: (OFString *)deviceID;
+
+/**
+ * @brief Adds the specified room ID to the list of joined rooms for the
+ *	  specified user ID.
+ *
+ * @param roomID The room ID to add to the list of joined rooms
+ * @param userID The user ID for which to add the room
+ */
+- (void)addJoinedRoom: (OFString *)roomID
+	      forUser: (OFString *)userID;
+
+/**
+ * @brief Removes the specified room ID to the list of joined rooms for the
+ *	  specified user ID.
+ *
+ * @param roomID The room ID to add to the list of joined rooms
+ * @param userID The user ID for which to add the room
+ */
+- (void)removeJoinedRoom: (OFString *)roomID
+		 forUser: (OFString *)userID;
+
+/**
+ * @brief Returns the joined room IDs for the specified user ID.
+ *
+ * @param userID The user ID for which to return the joined rooms
+ * @return The joined room IDs for the specified user ID
+ */
+- (OFArray<OFString *> *)joinedRoomsForUser: (OFString *)userID;
 @end
 
 OF_ASSUME_NONNULL_END