New feature `--lazy-db`: `--reuse-db` with `--create-db` on DB error / ProgrammingError

[blueyed]

What do you think about a new option --lazy-db, which would behave like --reuse-db, but falls back to --create-db when there's a DB error during the first test.

Would that be possible / feasible?
Could this be done by default, without a new option?

For example:

    def execute(self, sql, params=None):
        self.db.validate_no_broken_transaction()
        self.db.set_dirty()
        with self.db.wrap_database_errors:
            if params is None:
                return self.cursor.execute(sql)
            else:
>               return self.cursor.execute(sql, params)
E               ProgrammingError: relation "languages_plus_language" does not exist
E               LINE 1: ...."family", "languages_plus_language"."notes" FROM "languages...
E                                                                            ^

…/django-1.7.x/django/db/backends/utils.py:65: ProgrammingError

[pelme]

What would the outcome of that test be after the exception? Should db recreation happen and then the test be re-run? That would be a bit magic, but might be useful.

I see these kinds of errors when there are schema changes and I forgot to run with --create-db. Could we use migrations to migrate the test database to the correct state automatically, instead of re-running migrations from scratch?

[pelme]

(#220 is about running migrations with --reuse-db to make sure the database is up to date)

[jedie]

Is it possible to detect if there are new schema changes and then force "--create-db" ?