Foreign key for selected character slots.

Content.Server.Database/Model.cs

@@ -55,6 +55,12 @@ namespace Content.Server.Database
     [Table("preference")]
     public class Preference
     {
+        // NOTE: on postgres there SHOULD be an FK ensuring that the selected character slot always exists.
+        // I had to use a migration to implement it and as a result its creation is a finicky mess.
+        // Because if I let EFCore know about it it would explode on a circular reference.
+        // Also it has to be DEFERRABLE INITIALLY DEFERRED so that insertion of new preferences works.
+        // Also I couldn't figure out how to create it on SQLite.
+
         [Column("preference_id")] public int Id { get; set; }
         [Column("user_id")] public Guid UserId { get; set; }
         [Column("selected_character_slot")] public int SelectedCharacterSlot { get; set; }