SQLAlchemy Query.first() can't raise the NoResultFound exception

[Roman Podoliaka]

SQLAlchemy Query.first() is used incorrectly in this code fragment of quantum/plugins/nicira/nicira_qos_db.py:

       try:
            with context.session.begin(subtransactions=True):
                binding = query.filter_by(network_id=network_id).first()
                if binding:
                    context.session.delete(binding)
        except exc.NoResultFound:
            # return since this can happen if we are updating a port that
            # did not already have a queue on it. There is no need to check
            # if there is one before deleting if we return here.
            return

In fact, Query.first() doesn't raise the NoResultFound exception if no result is found but rather returns None.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/28571

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/28571
Committed: http://github.com/openstack/quantum/commit/6d26dd57680ddcdfc3c31fbe2d7190e0f6d28d0d
Submitter: Jenkins
Branch: master

commit 6d26dd57680ddcdfc3c31fbe2d7190e0f6d28d0d
Author: Roman Podolyaka <email address hidden>
Date: Wed May 8 18:34:51 2013 +0300

    Fix usage of SQLAlchemy Query.first() method

    Query.first() doesn't raise the NoResultFound exception
    if no result is found but rather returns None, so wrapping
    of Query.first() call into a try/except NoResultFound block
    is useless.

    Fixes bug 1177842.

    Change-Id: I0bd0e6d8299734b485dd1a1ac36bf6c295fd8932