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[Launchpad Bug Tracker <1174192@xxxxxxxxxxxxxxxxxx>]

[Expired for neutron because there has been no activity for 60 days.]

** Changed in: neutron
       Status: Incomplete => Expired

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https://bugs.launchpad.net/bugs/1174192

Title:
  Provide a way to load related collections using joins

Status in neutron:
  Expired

Bug description:
  It is a common pattern in our code to retrieve a collection using a
  model specific method (e. g. get_networks()/get_subnets()/etc) and
  process its elements in for loop. However this is not very database
  friendly if the model has related collections  that are lazy loaded
  (i. e. they are loaded by making an additional select query on
  attribute access), because this leads to (1 + N) queries to DB.

  We can actually analyze the list of queried fields and force
  loading of related collection using LEFT OUTER JOIN. This makes
  the original query more complex but prevents us from making of
  additional N queries.

  The idea is to modify generic _get_collection() method so that
  a caller may force it to use 'joinedload' strategy in different
  ways: use 'joinedload' for loading of specified related collections,
  use 'joinedload' for loading of all related collections that
  are queried, disable 'joinedload' and load related collections lazily
  on attribute access.

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