Comment 3 for bug 1414905

Reviewed: https://review.openstack.org/149458
Committed: https://git.openstack.org/cgit/openstack/neutron/commit/?id=5a480be4a806e9f9b6e87f217a43fcc5fd8553dc
Submitter: Jenkins
Branch: master

commit 5a480be4a806e9f9b6e87f217a43fcc5fd8553dc
Author: YAMAMOTO Takashi <email address hidden>
Date: Tue Jan 27 15:32:19 2015 +0900

    Fix a usage error of joinedload + filter in l3 scheduler

    This commit fixes admin_state_up filtering in
    get_l3_agents_hosting_routers. Also, adapt its callers
    which rely on the current broken implementation.

    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 RouterL3AgentBinding 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

    Partial-Bug: #1414905
    Closes-Bug: #1410841
    Change-Id: I2243cdfda5c6fe5ef67f96e3274d5381a6e50e62