Finished clean on recommendation engines

src/libs/database/impl/Artist.cpp

@@ -66,6 +66,13 @@ Artist::getById(Session& session, ArtistId id)
 	return session.getDboSession().find<Artist>().where("id = ?").bind(id).resultValue();
 }
 
+bool
+Artist::exists(Session& session, ArtistId id)
+{
+	session.checkSharedLocked();
+	return session.getDboSession().query<int>("SELECT 1 FROM artist").where("id = ?").bind(id).resultValue() == 1;
+}
+
 Artist::pointer
 Artist::create(Session& session, const std::string& name, const std::optional<UUID>& MBID)
 {

src/libs/database/impl/Release.cpp

@@ -114,6 +114,13 @@ Release::getById(Session& session, ReleaseId id)
 					.resultValue();
 }
 
+bool
+Release::exists(Session& session, ReleaseId id)
+{
+	session.checkSharedLocked();
+	return session.getDboSession().query<int>("SELECT 1 FROM release").where("id = ?").bind(id).resultValue() == 1;
+}
+
 Release::pointer
 Release::create(Session& session, const std::string& name, const std::optional<UUID>& MBID)
 {

src/libs/database/impl/Track.cpp

@@ -156,6 +156,14 @@ Track::getById(Session& session, TrackId id)
 		.resultValue();
 }
 
+bool
+Track::exists(Session& session, TrackId id)
+{
+	session.checkSharedLocked();
+
+	return session.getDboSession().query<int>("SELECT 1 from track").where("id = ?").bind(id).resultValue() == 1;
+}
+
 std::vector<Track::pointer>
 Track::getByRecordingMBID(Session& session, const UUID& mbid)
 {