QSQLITE option to use extended result codes

When the user tries to add a entity twice, the application should be able to tell him the error precisely.

Technically, a UNIQUE constraint is used in a SQLite database. When executing a insert query, using QSqlQuery, and it fails, I use query.lastError().nativeErrorCode().  (defined in QSqlError).

The problem is that it returns the code 19, which is SQLITE_CONSTRAINT, defined in sqlite3.h.

This error is to generic (it could be foreign key constraint error, etc..).

SQLite provides the concept of extended result codes.

For the above case , SQLITE_CONSTRAINT_UNIQUE (2067) should be returned.

As described in the SQLite documentation, returning extended result codes by default is disabled for historical compatibility reason.

SQLite provides a function to return extended reult codes by default.

My suggestion is to add connection option ( see QSqlDatabase::setConnectOptions() ): QSQLITE_USE_EXTENDED_RESULT_CODES .

 In QSQLiteDriver::open() method, sqlite3_extended_result_codes(d->access, 1) could be called if this option is set. I attached the modified qsql_sqlite.cpp .