The current design of QSqlDatabase is hostile to multithreading (which is quite common these days). For one, the public API forces anyone to add and remove databases to/from a global table, yet each thread can only access database objects created in its own, rendering the global table pointless. For two, the fact that a database objects cannot be moved poses serious design problems. No longer can QSqlDatabase be created at construction time; instead, a special init() function must be provided if a QObject is intended to live in another thread. In addition, any QObject has a non-overridable moveToThread() method, yet some of them (referring to any QSqlDatabase) must have thread affinity fixed or risk undefined behavior. I believe this violates Liskov substitution principle and thus pokes a hole in the objected oriented design.

To fix this, the global table should become optional. QSqlDatabase also must be allowed to move to another thread; or as what other database library do, be able to be accessed in any thread provided that it is not accessed simultaneously.