On Sunday 02 February 2014 23:08:05 Wlodek wrote:
> Hi all,
>
> I have doubt about mentioned test. Is it correct?
>
The test is correct for the backends in core.
> As context manager "constraint_checks_disabled" enables
> constraint checking upon exit which is before end of transaction (rollback)
> there will/should be IntegrityError raised?
>
That depends on the backend. For MySQL, you can (and the backend does) enable
the constraints without checking them on existing data, so no error is raised.
I don't know if you can force checks while enabling constraints on MySQL; you
can (and should) on MSSQL, which AFAIR doesn't have deferrable FKs -- and then
the test would fail. Although MSSQL is not in core, we should probably try
harder to be friendly towards it.
> As I understand this test passes for oracle/postgres because there
> is no implementation for "enable/disable_constraint_checking" for those
> backends?
>
Not exactly. The methods, as you say, do nothing -- so you could expect the
test to fail because the checks are never turned off. But Postgres and Oracle
have deferrable FKs -- which means the checks for FK constraints are only done
at transaction commit time; since the transaction is rolled back, nothing
fails.
There is one thing in the test (also the preceding test) which could be seen
as a little misleading -- the line "transaction.set_rollback(True)" only gets
executed when the test passes, because self.fail(...) raises an exception. You
don't see that in the code -- you would if it were in an "else" block" -- but
if you're familiar with tests, it shouldn't surprise you much.
HTH,
Shai.
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