Comment 28 for bug 1499647

Reviewed: https://review.openstack.org/238122
Committed: https://git.openstack.org/cgit/openstack/neutron/commit/?id=756864270aa87fadb4b2090f180577664cabc415
Submitter: Jenkins
Branch: master

commit 756864270aa87fadb4b2090f180577664cabc415
Author: Ann Kamyshnikova <email address hidden>
Date: Wed Oct 21 17:16:38 2015 +0300

    Add UniqueConstraint in L3HARouterAgentPortBinding

    It is expected that pair router_id and l3_agent_id will be unique
    in table ha_router_agent_port_bindings. As it appeared that
    duplicates can be added this change adds UniqueConstraint for
    this columns.

    Having duplicates is odd and leads to problems during sync_routers.

    DBReferenceError will be caught create_ha_port_and_bind and
    _bind_ha_router_to_agents(l3_agent_scheduler.py) as
    L3HARouterAgentPortBinding are created with l3_agent_id=None
    in _create_ha_port_binding (l3_hamode_db.py)

    Change-Id: I7ac2283752deaa3d9601b83859a46b9e89940269
    Partial-bug: #1499647