Comment 2 for bug 1414905

Reviewed: https://review.openstack.org/150284
Committed: https://git.openstack.org/cgit/openstack/neutron/commit/?id=96aa9f93600d6e97394ad725e095d5539848ca2d
Submitter: Jenkins
Branch: master

commit 96aa9f93600d6e97394ad725e095d5539848ca2d
Author: YAMAMOTO Takashi <email address hidden>
Date: Tue Jan 27 15:33:36 2015 +0900

    Fix a usage error of joinedload + filter in dhcp scheduler

    This commit fixes filtering in get_dhcp_agents_hosting_networks.

    Also, separate the argument "active" into two; active (heartbeat thing)
    and admin_state_up. Because all in-tree callers with active=True seem
    to mean only the former, currently the new admin_state_up argument is not
    used. (Thus this commit doesn't change any behaviour yet. The argument
    might be useful for other changes like [1])

    [1] https://review.openstack.org/#/c/147032/

    Details:

    With the current coding, joinedload() produces a JOIN and
    the following filter() on the columns from the joined table
    would create another JOIN of the same table. (As t1 in the
    following example). It doesn't seem to be the intended
    behaviour. As a consequence the filter (WHERE clause in
    the following examples) doesn't work as expected.

    Queries before this fix looked like the following,
    where t1 and t2 are Agent and NetworkDhcpAgentBinding respectively:

        SELECT t2.aaa, t1_1.bbb, ...
        FROM t1, t2 LEFT OUTER JOIN t1 AS t1_1 ON t1_1.ccc = t2.ddd
        WHERE t1.eee = ...;

    After the fix, it would be:

        SELECT t2.aaa, t1.bbb, ...
        FROM t2 JOIN t1 ON t1.ccc = t2.ddd
        WHERE t1.eee = ...;

    Reference: http://docs.sqlalchemy.org/en/rel_0_9/orm/loading_relationships.html#contains-eager

    Closes-Bug: #1414905
    Change-Id: Idf9ffdb849de58fba8c18c357ffa10cf0f398140