Re: [Django] #17001: Allow usage of custom querysets in prefetch_related

[Django]

#17001: Allow usage of custom querysets in prefetch_related
-+-
 Reporter:  akaariai |Owner:  loic84
 Type:  New feature  |   Status:  closed
Component:  Database layer   |  Version:  master
  (models, ORM)  |
 Severity:  Normal   |   Resolution:  fixed
 Keywords:  prefetch_related | Triage Stage:  Accepted
Has patch:  1|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-

Comment (by Simon Charette ):

 In [changeset:"5d240b070d744f9a2f4cc3117306ea861d866019" 5d240b0]:
 {{{
 #!CommitTicketReference repository=""
 revision="5d240b070d744f9a2f4cc3117306ea861d866019"
 Refs #17001 -- Added a test for custom prefetch related queryset on
 generic relations.
 }}}

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Re: [Django] #17001: Allow usage of custom querysets in prefetch_related

[Django]

#17001: Allow usage of custom querysets in prefetch_related
-+-
 Reporter:  akaariai |Owner:  loic84
 Type:  New feature  |   Status:  closed
Component:  Database layer   |  Version:  master
  (models, ORM)  |   Resolution:  fixed
 Severity:  Normal   | Triage Stage:  Accepted
 Keywords:  prefetch_related |  Needs documentation:  0
Has patch:  1|  Patch needs improvement:  0
  Needs tests:  0|UI/UX:  0
Easy pickings:  0|
-+-

Comment (by Loic Bistuer ):

 In [changeset:"0fa1aeb8d8142bd6bceb0c9a36c8e42eeca21770"]:
 {{{
 #!CommitTicketReference repository=""
 revision="0fa1aeb8d8142bd6bceb0c9a36c8e42eeca21770"
 [1.7.x] Fixed the ordering of prefetch lookups so that latter lookups can
 refer to former lookups.

 Thanks Anssi Kääriäinen and Tim Graham for the reviews. Refs #17001 and
 #22650.

 Backport of 870b0a1f86 from master
 }}}

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Re: [Django] #17001: Allow usage of custom querysets in prefetch_related

[Django]

#17001: Allow usage of custom querysets in prefetch_related
-+-
 Reporter:  akaariai |Owner:  loic84
 Type:  New feature  |   Status:  closed
Component:  Database layer   |  Version:  master
  (models, ORM)  |   Resolution:  fixed
 Severity:  Normal   | Triage Stage:  Accepted
 Keywords:  prefetch_related |  Needs documentation:  0
Has patch:  1|  Patch needs improvement:  0
  Needs tests:  0|UI/UX:  0
Easy pickings:  0|
-+-

Comment (by Loic Bistuer ):

 In [changeset:"24a41ecc3590f8d92d085d4a4caa5f8bf962ceae"]:
 {{{
 #!CommitTicketReference repository=""
 revision="24a41ecc3590f8d92d085d4a4caa5f8bf962ceae"
 [1.7.x] Fixed #22650 -- Fixed regression on prefetch_related.

 Regression from f51c1f59 when using select_related then prefetch_related
 on the reverse side of an O2O:

 Author.objects.select_related('bio').prefetch_related('bio__books')

 Thanks Aymeric Augustin for the report and tests. Refs #17001.

 Backport of bdf3473e64 from master
 }}}

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Re: [Django] #17001: Allow usage of custom querysets in prefetch_related

[Django]

#17001: Allow usage of custom querysets in prefetch_related
-+-
 Reporter:  akaariai |Owner:  loic84
 Type:  New feature  |   Status:  closed
Component:  Database layer   |  Version:  master
  (models, ORM)  |   Resolution:  fixed
 Severity:  Normal   | Triage Stage:  Accepted
 Keywords:  prefetch_related |  Needs documentation:  0
Has patch:  1|  Patch needs improvement:  0
  Needs tests:  0|UI/UX:  0
Easy pickings:  0|
-+-

Comment (by Loic Bistuer ):

 In [changeset:"bdf3473e64879d196e79fe8832cdacc6efb68150"]:
 {{{
 #!CommitTicketReference repository=""
 revision="bdf3473e64879d196e79fe8832cdacc6efb68150"
 Fixed #22650 -- Fixed regression on prefetch_related.

 Regression from f51c1f59 when using select_related then prefetch_related
 on the reverse side of an O2O:

 Author.objects.select_related('bio').prefetch_related('bio__books')

 Thanks Aymeric Augustin for the report and tests. Refs #17001.
 }}}

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Re: [Django] #17001: Allow usage of custom querysets in prefetch_related

[Django]

#17001: Allow usage of custom querysets in prefetch_related
-+-
 Reporter:  akaariai |Owner:  loic84
 Type:  New feature  |   Status:  closed
Component:  Database layer   |  Version:  master
  (models, ORM)  |   Resolution:  fixed
 Severity:  Normal   | Triage Stage:  Accepted
 Keywords:  prefetch_related |  Needs documentation:  0
Has patch:  1|  Patch needs improvement:  0
  Needs tests:  0|UI/UX:  0
Easy pickings:  0|
-+-

Comment (by Loic Bistuer ):

 In [changeset:"870b0a1f8689aa8fd4806623262228b8ac3a88a5"]:
 {{{
 #!CommitTicketReference repository=""
 revision="870b0a1f8689aa8fd4806623262228b8ac3a88a5"
 Fixed the ordering of prefetch lookups so that latter lookups can refer to
 former lookups.

 Thanks Anssi Kääriäinen and Tim Graham for the reviews. Refs #17001 and
 #22650.
 }}}

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Re: [Django] #17001: Allow usage of custom querysets in prefetch_related

[Django]

#17001: Allow usage of custom querysets in prefetch_related
-+-
 Reporter:  akaariai |Owner:  loic84
 Type:  New feature  |   Status:  closed
Component:  Database layer   |  Version:  master
  (models, ORM)  |   Resolution:  fixed
 Severity:  Normal   | Triage Stage:  Accepted
 Keywords:  prefetch_related |  Needs documentation:  0
Has patch:  1|  Patch needs improvement:  0
  Needs tests:  0|UI/UX:  0
Easy pickings:  0|
-+-

Comment (by Anssi Kääriäinen ):

 In [changeset:"7bbb6958dcb6a450f926e5bb49b07391f801aef1"]:
 {{{
 #!CommitTicketReference repository=""
 revision="7bbb6958dcb6a450f926e5bb49b07391f801aef1"
 Allowed custom querysets when prefetching single valued relations

 The original patch for custom prefetches didn't allow usage of custom
 queryset for single valued relations (along ForeignKey or OneToOneKey).
 Allowing these enables calling performance oriented queryset methods like
 select_related or defer/only.

 Thanks @akaariai and @timgraham for the reviews. Refs #17001.
 }}}

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Re: [Django] #17001: Allow usage of custom querysets in prefetch_related

[Django]

#17001: Allow usage of custom querysets in prefetch_related
-+-
 Reporter:  akaariai |Owner:  loic84
 Type:  New feature  |   Status:  closed
Component:  Database layer   |  Version:  master
  (models, ORM)  |   Resolution:  fixed
 Severity:  Normal   | Triage Stage:  Accepted
 Keywords:  prefetch_related |  Needs documentation:  0
Has patch:  1|  Patch needs improvement:  0
  Needs tests:  0|UI/UX:  0
Easy pickings:  0|
-+-

Comment (by abdulwahid):

 Thanks for you help.

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Re: [Django] #17001: Allow usage of custom querysets in prefetch_related

[Django]

#17001: Allow usage of custom querysets in prefetch_related
-+-
 Reporter:  akaariai |Owner:  loic84
 Type:  New feature  |   Status:  closed
Component:  Database layer   |  Version:  master
  (models, ORM)  |   Resolution:  fixed
 Severity:  Normal   | Triage Stage:  Accepted
 Keywords:  prefetch_related |  Needs documentation:  0
Has patch:  1|  Patch needs improvement:  0
  Needs tests:  0|UI/UX:  0
Easy pickings:  0|
-+-

Comment (by loic84):

 @abdulwahid `QuerySet.latest()` doesn't return a `QuerySet` instance, so
 you can't pass it as the `queryset` kwarg of `prefetch_related`, maybe you
 meant `order_by('-start_time')` instead?

 I'm afraid I can't help you much more than that here, trac tickets aren't
 meant as a support channel, you can find me on #django on IRC if you want.

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Re: [Django] #17001: Allow usage of custom querysets in prefetch_related

[Django]

#17001: Allow usage of custom querysets in prefetch_related
-+-
 Reporter:  akaariai |Owner:  loic84
 Type:  New feature  |   Status:  closed
Component:  Database layer   |  Version:  master
  (models, ORM)  |   Resolution:  fixed
 Severity:  Normal   | Triage Stage:  Accepted
 Keywords:  prefetch_related |  Needs documentation:  0
Has patch:  1|  Patch needs improvement:  0
  Needs tests:  0|UI/UX:  0
Easy pickings:  0|
-+-

Comment (by abdulwahid):

 Hi loic84,

 I was trying it since morning but i found it very hard to build backport
 manually, i tried to integrated all changes related to
 "get_prefetch_queryset" and i did changes as per your changes
 
[https://code.djangoproject.com/changeset/f51c1f590085556abca44fd2a49618162203b2ec]
 in following files.
 1.django/contrib/contenttypes/generic.py
 2.django/db/models/__init__.py
 3.django/db/models/query.py
 4.django/db/models/fields/related.py

 also add one more file as it require for LOOKUP_SEP
 5.django/db/models/constants.py

 It works fine with following query

 
Person.objects.filter(profile__person_type__name='Speaker').prefetch_related(Prefetch('event_speaker',
 queryset=Event.objects.all())).

 But when i run

 
Person.objects.filter(profile__person_type__name='Speaker').prefetch_related(Prefetch('event_speaker',queryset=Event.objects.latest('start_time')))

 gives error

 ''AttributeError: 'Event' object has no attribute '_add_hints''' here
 'Event' is my table name.

 I stuck here and failed to resolve this.

 Could you help me out to overcome this issue.

 Note:

 I just want to fire a query which return its related data in queryset only
 so that i can avoid for loop to access the related data as
 "[obj.relate_data for obj in objects]" to achieve optimization.

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Re: [Django] #17001: Allow usage of custom querysets in prefetch_related

[Django]

#17001: Allow usage of custom querysets in prefetch_related
-+-
 Reporter:  akaariai |Owner:  loic84
 Type:  New feature  |   Status:  closed
Component:  Database layer   |  Version:  master
  (models, ORM)  |   Resolution:  fixed
 Severity:  Normal   | Triage Stage:  Accepted
 Keywords:  prefetch_related |  Needs documentation:  0
Has patch:  1|  Patch needs improvement:  0
  Needs tests:  0|UI/UX:  0
Easy pickings:  0|
-+-

Comment (by loic84):

 @abdulwahid24 it shouldn't be too hard to backport this patch manually,
 just note that the `get_prefetch_queryset` methods used to be called
 `get_prefetch_query_set`, other than that I don't think the code for
 prefetching has significantly changed since 1.4.

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Re: [Django] #17001: Allow usage of custom querysets in prefetch_related

[Django]

#17001: Allow usage of custom querysets in prefetch_related
-+-
 Reporter:  akaariai |Owner:  loic84
 Type:  New feature  |   Status:  closed
Component:  Database layer   |  Version:  master
  (models, ORM)  |   Resolution:  fixed
 Severity:  Normal   | Triage Stage:  Accepted
 Keywords:  prefetch_related |  Needs documentation:  0
Has patch:  1|  Patch needs improvement:  0
  Needs tests:  0|UI/UX:  0
Easy pickings:  0|
-+-

Comment (by abdulwahid24@…):

 Hi guys,

 How would i integrate this patch in Django 1.4.5 as i need this in my
 existing project running on production.

 Thanks,

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Re: [Django] #17001: Allow usage of custom querysets in prefetch_related

[Django]

#17001: Allow usage of custom querysets in prefetch_related
-+-
 Reporter:  akaariai |Owner:  loic84
 Type:  New feature  |   Status:  closed
Component:  Database layer   |  Version:  master
  (models, ORM)  |   Resolution:  fixed
 Severity:  Normal   | Triage Stage:  Accepted
 Keywords:  prefetch_related |  Needs documentation:  0
Has patch:  1|  Patch needs improvement:  0
  Needs tests:  0|UI/UX:  0
Easy pickings:  0|
-+-
Changes (by Anssi Kääriäinen ):

 * status:  assigned => closed
 * resolution:   => fixed


Comment:

 In [changeset:"f51c1f590085556abca44fd2a49618162203b2ec"]:
 {{{
 #!CommitTicketReference repository=""
 revision="f51c1f590085556abca44fd2a49618162203b2ec"
 Fixed #17001 -- Custom querysets for prefetch_related.

 This patch introduces the Prefetch object which allows customizing
 prefetch
 operations.

 This enables things like filtering prefetched relations, calling
 select_related
 from a prefetched relation, or prefetching the same relation multiple
 times
 with different querysets.

 When a Prefetch instance specifies a to_attr argument, the result is
 stored
 in a list rather than a QuerySet. This has the fortunate consequence of
 being
 significantly faster. The preformance improvement is due to the fact that
 we
 save the costly creation of a QuerySet instance.

 Thanks @akaariai for the original patch and @bmispelon and @timgraham
 for the reviews.
 }}}

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Re: [Django] #17001: Allow usage of custom querysets in prefetch_related

[Django]

#17001: Allow usage of custom querysets in prefetch_related
-+-
 Reporter:  akaariai |Owner:  loic84
 Type:  New feature  |   Status:  assigned
Component:  Database layer   |  Version:  master
  (models, ORM)  |   Resolution:
 Severity:  Normal   | Triage Stage:  Accepted
 Keywords:  prefetch_related |  Needs documentation:  0
Has patch:  1|  Patch needs improvement:  0
  Needs tests:  0|UI/UX:  0
Easy pickings:  0|
-+-

Comment (by loic84):

 Tackled the multidb issue described on the ML post and rebased to the
 latest master.

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Re: [Django] #17001: Allow usage of custom querysets in prefetch_related

[Django]

#17001: Allow usage of custom querysets in prefetch_related
-+-
 Reporter:  akaariai |Owner:  loic84
 Type:  New feature  |   Status:  assigned
Component:  Database layer   |  Version:  master
  (models, ORM)  |   Resolution:
 Severity:  Normal   | Triage Stage:  Accepted
 Keywords:  prefetch_related |  Needs documentation:  0
Has patch:  1|  Patch needs improvement:  0
  Needs tests:  0|UI/UX:  0
Easy pickings:  0|
-+-

Comment (by loic84):

 @akaariai wrote a great summary of the status of this patch on the django-
 developers mailing list: https://groups.google.com/d/msg/django-
 developers/LhXpbpSOHlg/n8xKrpFcvyMJ.

 Feedback would definitely help to move this ticket forward.

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Re: [Django] #17001: Allow usage of custom querysets in prefetch_related

[Django]

#17001: Allow usage of custom querysets in prefetch_related
-+-
 Reporter:  akaariai |Owner:  loic84
 Type:  New feature  |   Status:  assigned
Component:  Database layer   |  Version:  master
  (models, ORM)  |   Resolution:
 Severity:  Normal   | Triage Stage:  Accepted
 Keywords:  prefetch_related |  Needs documentation:  0
Has patch:  1|  Patch needs improvement:  0
  Needs tests:  0|UI/UX:  0
Easy pickings:  0|
-+-
Changes (by loic84):

 * needs_better_patch:  1 => 0
 * needs_docs:  1 => 0


Comment:

 Updated the PR with docs, and even more tests.

 This should be ready for deep review.

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Re: [Django] #17001: Allow usage of custom querysets in prefetch_related

[Django]

#17001: Allow usage of custom querysets in prefetch_related
-+-
 Reporter:  akaariai |Owner:  loic84
 Type:  New feature  |   Status:  assigned
Component:  Database layer   |  Version:  master
  (models, ORM)  |   Resolution:
 Severity:  Normal   | Triage Stage:  Accepted
 Keywords:  prefetch_related |  Needs documentation:  1
Has patch:  1|  Patch needs improvement:  1
  Needs tests:  0|UI/UX:  0
Easy pickings:  0|
-+-
Changes (by loic84):

 * needs_tests:  1 => 0


Comment:

 `to_attr` is back, cleaned up implementation and added a fair amount of
 tests. I'll tackle the docs ASAP.

 Made a PR https://github.com/django/django/pull/1826 to ease with review.

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Re: [Django] #17001: Allow usage of custom querysets in prefetch_related

[Django]

#17001: Allow usage of custom querysets in prefetch_related
-+-
 Reporter:  akaariai |Owner:  loic84
 Type:  New feature  |   Status:  assigned
Component:  Database layer   |  Version:  master
  (models, ORM)  |   Resolution:
 Severity:  Normal   | Triage Stage:  Accepted
 Keywords:  prefetch_related |  Needs documentation:  1
Has patch:  1|  Patch needs improvement:  1
  Needs tests:  1|UI/UX:  0
Easy pickings:  0|
-+-

Comment (by mjtamlyn):

 I'm happy to have `to_attr` back as well, especially if it makes the code
 cleaner. This is a good smell.

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Re: [Django] #17001: Allow usage of custom querysets in prefetch_related

[Django]

#17001: Allow usage of custom querysets in prefetch_related
-+-
 Reporter:  akaariai |Owner:  loic84
 Type:  New feature  |   Status:  assigned
Component:  Database layer   |  Version:  master
  (models, ORM)  |   Resolution:
 Severity:  Normal   | Triage Stage:  Accepted
 Keywords:  prefetch_related |  Needs documentation:  1
Has patch:  1|  Patch needs improvement:  1
  Needs tests:  1|UI/UX:  0
Easy pickings:  0|
-+-

Comment (by charettes):

 In the light of @akaariai's comment concerning kwargs the only other
 alternative I could think of was to rely on a `Prefetch` instance creation
 counter to sort `kwargs` but as @loic84 pointed out in IRC it would be
 quite fragile.

 I'd say I also favor the `to_attr` approach since it looks like the most
 sane way to avoid chaining `prefetch_related` to declare an ordering.

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Re: [Django] #17001: Allow usage of custom querysets in prefetch_related

[Django]

#17001: Allow usage of custom querysets in prefetch_related
-+-
 Reporter:  akaariai |Owner:  loic84
 Type:  New feature  |   Status:  assigned
Component:  Database layer   |  Version:  master
  (models, ORM)  |   Resolution:
 Severity:  Normal   | Triage Stage:  Accepted
 Keywords:  prefetch_related |  Needs documentation:  1
Has patch:  1|  Patch needs improvement:  1
  Needs tests:  1|UI/UX:  0
Easy pickings:  0|
-+-

Comment (by loic84):

 As @akaariai pointed out in #comment:24, `kwargs` are not ordered; yet
 ordering matters a fair bit.

 For example my example from the previous comment:

 {{{#!python
 Restaurant.objects.prefetch_related(
 'pizza_list__toppings_list',
  pizza_list=Prefetch('pizza'),
 )
 }}}

 This wouldn't work without some
 [https://github.com/loic/django/compare/prefetch_related#diff-
 5b0dda5eb9a242c15879dc9cd2121379R1652 sorting in the implementation].

 I then found out that `*args` ordering is something
 
[https://github.com/django/django/blob/master/tests/prefetch_related/tests.py#L453
 we actually test for], even though it doesn't seem documented. This
 implicit ordering allows for `@properties` to
 
[https://github.com/django/django/blob/master/tests/prefetch_related/models.py#L177
 masquerade as managers].

 Sorting by lookup like in my patch, would obviously mess that up.

 We could:

 1. Do the sorting based on the lookup path and add an `after` argument to
 the `Prefetch` object, so you could do
 `prefetch_related(Prefetch('primary_house__occupants',
 after='houses__rooms'), 'houses__rooms')`. This would actually be backward
 **incompatible** for whomever already rely on the implicit ordering of
 `*args`, since you need to opt-in for a custom `after`.

 2. Require multiple calls to `prefetch_related()` when ordering matters:
 
`prefetch_related(pizza_list=Prefetch('pizza')).prefetch_related('pizza_list__toppings_list')`.
 IMO this adds yet another construct to an already complicated API.

 3. Go back to having `to_attr` as a `Prefetch` argument rather than a
 `kwarg`, and finally document that ordering of `*args` actually matters.
 This is backward **compatible**, and it also makes for a **cleaner
 implementation**. I was actually on the verge of adding it (undocumented),
 only for the purpose of cleaning up the current implementation.

 For the record, I favor 3) by a big margin.

 Please note that while `prefetch_related('foo__bar__baz', 'foo__bar')`
 and `prefetch_related('foo__bar', 'foo__bar__baz')` were equivalent, it's
 not necessarily true anymore now that we can do
 `prefetch_related(Prefetch('foo__bar', queryset=...), 'foo__bar__baz')`,
 so the actual ordering becomes a more prominent concern than before.

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Re: [Django] #17001: Allow usage of custom querysets in prefetch_related

[Django]

#17001: Allow usage of custom querysets in prefetch_related
-+-
 Reporter:  akaariai |Owner:  loic84
 Type:  New feature  |   Status:  assigned
Component:  Database layer   |  Version:  master
  (models, ORM)  |   Resolution:
 Severity:  Normal   | Triage Stage:  Accepted
 Keywords:  prefetch_related |  Needs documentation:  1
Has patch:  1|  Patch needs improvement:  1
  Needs tests:  1|UI/UX:  0
Easy pickings:  0|
-+-

Comment (by loic84):

 WIP: https://github.com/loic/django/compare/prefetch_related.

 It's rather experimental and still needs tons of work with tests and docs,
 but if anyone want to give it a try, that would help.

 `Prefetch` takes two parameters: `lookup` and an optional `queryset`.

 1. `Manager` backed lookups with `*args`:

 {{{#!python
 # Traditional string lookup:
 Restaurant.objects.prefetch_related('pizzas__toppings')

 # Equivalent with Prefetch:
 Restaurant.objects.prefetch_related(Prefetch('pizzas__toppings'))

 # Lookup with custom queryset:
 Restaurant.objects.prefetch_related(
 Prefetch('pizzas__toppings',
 queryset=Toppings.object.filter(veggie=True)))
 }}}

 2. `list` backed lookups with `**kwargs`:

 {{{#!python
 # Traditional lookup stored in a list (significantly faster, see
 #20577 and link below)
 Restaurant.objects.prefetch_related(pizza_list=Prefetch('pizzas'))

 # With custom QuerySet.
 Pizza.objects.prefetch_related(
 toppings_list=Prefetch('toppings',
 queryset=Toppings.object.filter(veggie=True))

 # Multiple level using nested prefetch_related:
 pizza_queryset = Pizza.objects.prefetch_related(
 Prefetch('toppings',
 queryset=Toppings.object.filter(veggie=True)))
 Restaurant.objects.prefetch_related(
 pizza_list=Prefetch('pizzas', queryset=pizza_queryset))

 # Alternatively, multiple level using kwarg lookups (nested
 prefetch_related actually rewrite to that):
 Restaurant.objects.prefetch_related(
 pizza_list=Prefetch('pizzas'),
 pizza_list__toppings_list=Prefetch('pizza_list__toppings',
 queryset=Toppings.object.filter(veggie=True))
 }}}

 3. Mixing both approaches:

 {{{#!python
 Restaurant.objects.prefetch_related(
 'pizza_list__toppings_list'
 'pizza_list': Prefetch('pizza'),
 )

 }}}

 4. Flattening is **not** supported, it doesn't seem trivial to implement,
 maybe for another ticket?

 {{{#!python
 Restaurant.objects.prefetch_related(
 toppings_list=Prefetch('pizzas__toppings')
 )
 }}}

 Additionally, here is a quick and dirty benchmark that compares lookups
 backed by `list` vs `Manager`:  https://gist.github.com/loic/7198193.

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Re: [Django] #17001: Allow usage of custom querysets in prefetch_related

[Django]

#17001: Allow usage of custom querysets in prefetch_related
-+-
 Reporter:  akaariai |Owner:  loic84
 Type:  New feature  |   Status:  assigned
Component:  Database layer   |  Version:  master
  (models, ORM)  |   Resolution:
 Severity:  Normal   | Triage Stage:  Accepted
 Keywords:  prefetch_related |  Needs documentation:  1
Has patch:  1|  Patch needs improvement:  1
  Needs tests:  1|UI/UX:  0
Easy pickings:  0|
-+-
Changes (by loic84):

 * status:  new => assigned
 * owner:  nobody => loic84
 * version:  1.3 => master


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Re: [Django] #17001: Allow usage of custom querysets in prefetch_related

[Django]

#17001: Allow usage of custom querysets in prefetch_related
-+-
 Reporter:  akaariai |Owner:  nobody
 Type:  New feature  |   Status:  new
Component:  Database layer   |  Version:  1.3
  (models, ORM)  |   Resolution:
 Severity:  Normal   | Triage Stage:  Accepted
 Keywords:  prefetch_related |  Needs documentation:  1
Has patch:  1|  Patch needs improvement:  1
  Needs tests:  1|UI/UX:  0
Easy pickings:  0|
-+-
Changes (by jonatan.lundin@…):

 * cc: jonatan.lundin@… (added)


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Re: [Django] #17001: Allow usage of custom querysets in prefetch_related

[Django]

#17001: Allow usage of custom querysets in prefetch_related
-+-
 Reporter:  akaariai |Owner:  nobody
 Type:  New feature  |   Status:  new
Component:  Database layer   |  Version:  1.3
  (models, ORM)  |   Resolution:
 Severity:  Normal   | Triage Stage:  Accepted
 Keywords:  prefetch_related |  Needs documentation:  1
Has patch:  1|  Patch needs improvement:  1
  Needs tests:  1|UI/UX:  0
Easy pickings:  0|
-+-
Changes (by mszamot@…):

 * cc: mszamot@… (added)


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Re: [Django] #17001: Allow usage of custom querysets in prefetch_related

[Django]

#17001: Allow usage of custom querysets in prefetch_related
-+-
 Reporter:  akaariai |Owner:  nobody
 Type:  New feature  |   Status:  new
Component:  Database layer   |  Version:  1.3
  (models, ORM)  |   Resolution:
 Severity:  Normal   | Triage Stage:  Accepted
 Keywords:  prefetch_related |  Needs documentation:  1
Has patch:  1|  Patch needs improvement:  1
  Needs tests:  1|UI/UX:  0
Easy pickings:  0|
-+-
Changes (by ryanhiebert):

 * cc: ryanhiebert (removed)


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Re: [Django] #17001: Allow usage of custom querysets in prefetch_related

[Django]

#17001: Allow usage of custom querysets in prefetch_related
-+-
 Reporter:  akaariai |Owner:  nobody
 Type:  New feature  |   Status:  new
Component:  Database layer   |  Version:  1.3
  (models, ORM)  |   Resolution:
 Severity:  Normal   | Triage Stage:  Accepted
 Keywords:  prefetch_related |  Needs documentation:  1
Has patch:  1|  Patch needs improvement:  1
  Needs tests:  1|UI/UX:  0
Easy pickings:  0|
-+-
Changes (by ryanhiebert):

 * cc: ryanhiebert (added)


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Re: [Django] #17001: Allow usage of custom querysets in prefetch_related

[Django]

#17001: Allow usage of custom querysets in prefetch_related
-+-
 Reporter:  akaariai |Owner:  nobody
 Type:  New feature  |   Status:  new
Component:  Database layer   |  Version:  1.3
  (models, ORM)  |   Resolution:
 Severity:  Normal   | Triage Stage:  Accepted
 Keywords:  prefetch_related |  Needs documentation:  1
Has patch:  1|  Patch needs improvement:  1
  Needs tests:  1|UI/UX:  0
Easy pickings:  0|
-+-

Comment (by mjtamlyn):

 +1 to that syntax, seems a good middle ground.

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Re: [Django] #17001: Allow usage of custom querysets in prefetch_related

[Django]

#17001: Allow usage of custom querysets in prefetch_related
-+-
 Reporter:  akaariai |Owner:  nobody
 Type:  New feature  |   Status:  new
Component:  Database layer   |  Version:  1.3
  (models, ORM)  |   Resolution:
 Severity:  Normal   | Triage Stage:  Accepted
 Keywords:  prefetch_related |  Needs documentation:  1
Has patch:  1|  Patch needs improvement:  1
  Needs tests:  1|UI/UX:  0
Easy pickings:  0|
-+-

Comment (by akaariai):

 I have discussed this issue with multiple people on #django-dev. It seems
 kwargs based API is favoured. Lets do that.

 The syntax is:
 {{{
 qs = SomeModel.objects.prefetch_related(
 rel_pk_ordered=Prefetch('rel_model',
 RelModel.objects.order_by('-pk')),
 )
 }}}
 This means that the objects fetched will have rel_pk_ordered each,
 containing objects through relation 'rel_model' using given queryset. It
 is not possible to chain prefetches to custom prefetches, instead one
 should do:
 {{{
 qs = SomeModel.objects.prefetch_related(
 rel_pk_ordered=Prefetch('rel_model',
 RelModel.objects.order_by('-pk').prefetch_related(...)),
 )
 }}}
 that is, issue the prefetch in the given custom queryset.

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Re: [Django] #17001: Allow usage of custom querysets in prefetch_related

[Django]

#17001: Allow usage of custom querysets in prefetch_related
-+-
 Reporter:  akaariai |Owner:  nobody
 Type:  New feature  |   Status:  new
Component:  Database layer   |  Version:  1.3
  (models, ORM)  |   Resolution:
 Severity:  Normal   | Triage Stage:  Accepted
 Keywords:  prefetch_related |  Needs documentation:  1
Has patch:  1|  Patch needs improvement:  1
  Needs tests:  1|UI/UX:  0
Easy pickings:  0|
-+-

Comment (by chokosabe):

 I am more than happy to help with testing on this (or anything else that
 might need doing). There is no shortage of ideas on this; some(one/people)
 that can make a decision on this just need to do so

 Hate to point this out; can't imagine this (ongoing) discussion happening
 with a rails feature something would have been added already (it may
 well not be perfect or even right)...

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Re: [Django] #17001: Allow usage of custom querysets in prefetch_related

[Django]

#17001: Allow usage of custom querysets in prefetch_related
-+-
 Reporter:  akaariai |Owner:  nobody
 Type:  New feature  |   Status:  new
Component:  Database layer   |  Version:  1.3
  (models, ORM)  |   Resolution:
 Severity:  Normal   | Triage Stage:  Accepted
 Keywords:  prefetch_related |  Needs documentation:  1
Has patch:  1|  Patch needs improvement:  1
  Needs tests:  1|UI/UX:  0
Easy pickings:  0|
-+-

Comment (by akaariai):

 I also like the kwargs based syntax. Maybe we should change the API to
 that?

 One thing to consider is that kwargs aren't ordered. So, the API must not
 assume ordering there.

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Re: [Django] #17001: Allow usage of custom querysets in prefetch_related

[Django]

#17001: Allow usage of custom querysets in prefetch_related
-+-
 Reporter:  akaariai |Owner:  nobody
 Type:  New feature  |   Status:  new
Component:  Database layer   |  Version:  1.3
  (models, ORM)  |   Resolution:
 Severity:  Normal   | Triage Stage:  Accepted
 Keywords:  prefetch_related |  Needs documentation:  1
Has patch:  1|  Patch needs improvement:  1
  Needs tests:  1|UI/UX:  0
Easy pickings:  0|
-+-
Changes (by alexpirine):

 * cc: as@… (added)


Comment:

 Replying to [comment:22 FunkyBob]:
 > To express that in the comment above:
 > {{{
 > qs = SomeModel.objects.prefetch_related(
 > foo_list=Prefetch('rel_model', RelModel.objects.order_by('-pk')),
 > anot_lst=Prefetch('foo_lst__another_model',
 AnotModel.objects.order_by('-pk')),
 > )
 > }}}

 This syntax seems very nice, I like how it is even more concise without
 `to_attr`.

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Re: [Django] #17001: Allow usage of custom querysets in prefetch_related

[Django]

#17001: Allow usage of custom querysets in prefetch_related
-+-
 Reporter:  akaariai |Owner:  nobody
 Type:  New feature  |   Status:  new
Component:  Database layer   |  Version:  1.3
  (models, ORM)  |   Resolution:
 Severity:  Normal   | Triage Stage:  Accepted
 Keywords:  prefetch_related |  Needs documentation:  1
Has patch:  1|  Patch needs improvement:  1
  Needs tests:  1|UI/UX:  0
Easy pickings:  0|
-+-

Comment (by FunkyBob):

 This follows some discussion on IRC with loic and akaariai...

 Perhaps a more keywordy syntax?

 To express that in the comment above:
 {{{
 qs = SomeModel.objects.prefetch_related(
 foo_list=Prefetch('rel_model', RelModel.objects.order_by('-pk')),
 anot_lst=Prefetch('foo_lst__another_model',
 AnotModel.objects.order_by('-pk')),
 )
 }}}

 This also means you can avoid the repeated QS-copy cost for adding
 multiple prefetches.

 And, as loic pointed out, you can get the "terse" syntax simply using:

 {{{
 from  import Prefetch as R
 }}}

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Re: [Django] #17001: Allow usage of custom querysets in prefetch_related

[Django]

#17001: Allow usage of custom querysets in prefetch_related
-+-
 Reporter:  akaariai |Owner:  nobody
 Type:  New feature  |   Status:  new
Component:  Database layer   |  Version:  1.3
  (models, ORM)  |   Resolution:
 Severity:  Normal   | Triage Stage:  Accepted
 Keywords:  prefetch_related |  Needs documentation:  1
Has patch:  1|  Patch needs improvement:  1
  Needs tests:  1|UI/UX:  0
Easy pickings:  0|
-+-

Comment (by alexpirine):

 I am interested in this feature, so please don't take the following as a
 criticism, I am just trying to add a feedback from a Django user
 perspective.

 I am trying to understand, what is wrong with the initial implementation
 using the R objects?

 We already have “F” and “Q” objects for “advanced” queries, so why not “R”
 objects for some other “advanced” stuff?

 The code looks less clear when you begin to mix object names and various
 parameters in `prefetch_related()`, and `.prefetch_related('authors',
 to_attr='authors_by_age',
 queryset=Author.objects.order_by('age').prefetch_related('books'))` seems
 really weird and inconsistent with the current possibility of
 `prefetch_related('authors_by_age__books')`.

 Just to take the original example for comparison:

 {{{
 qs = SomeModel.objects.prefetch_related(
R('rel_model', qs=RelModel.objects.order_by('-pk'), to_attr='foo_lst'),
R('foo_lst__another_model', qs=AnotModel.objects.order_by('-pk'),
 to_attr='anot_lst')
 )
 }}}

 How does it translates in the new API since chaining is not allowed?

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Re: [Django] #17001: Allow usage of custom querysets in prefetch_related

[Django]

#17001: Allow usage of custom querysets in prefetch_related
-+-
 Reporter:  akaariai |Owner:  nobody
 Type:  New feature  |   Status:  new
Component:  Database layer   |  Version:  1.3
  (models, ORM)  |   Resolution:
 Severity:  Normal   | Triage Stage:  Accepted
 Keywords:  prefetch_related |  Needs documentation:  1
Has patch:  1|  Patch needs improvement:  1
  Needs tests:  1|UI/UX:  0
Easy pickings:  0|
-+-

Comment (by mjtamlyn):

 Replying to [comment:19 akaariai]:

 > For the first implementation making sure fetching basic querysets works
 well should be enough. For example, if it turns out it will be hard to
 support prefetching values() querysets or generic relations, then throwing
 an error and documenting what doesn't work seems good enough.

 Agreed. If it's trickier than just getting this patch in needs to be we
 can always delay it for a future patch.

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Re: [Django] #17001: Allow usage of custom querysets in prefetch_related

[Django]

#17001: Allow usage of custom querysets in prefetch_related
-+-
 Reporter:  akaariai |Owner:  nobody
 Type:  New feature  |   Status:  new
Component:  Database layer   |  Version:  1.3
  (models, ORM)  |   Resolution:
 Severity:  Normal   | Triage Stage:  Accepted
 Keywords:  prefetch_related |  Needs documentation:  1
Has patch:  1|  Patch needs improvement:  1
  Needs tests:  1|UI/UX:  0
Easy pickings:  0|
-+-

Comment (by akaariai):

 Lets accept the proposed API. There weren't any objections, and at least
 two core developers (me + mjtamlyn) support this API. The proposed API
 feels more natural than the R() thing, and it should be powerful enough.

 The accepted API is to add an overloaded form of .prefetch_related(). The
 current way works as always, that is `.prefetch_related('somemodel',
 'somemodel__someothermodel')` will continue to work. The new alternative
 is `.prefetch_related('authors', to_attr='authors_by_age',
 queryset=Author.objects.order_by('age'))`.

 Chaining to prefetched custom queryset isn't allowed, that is in the above
 example you can't do `.prefetch_related('authors_by_age__books')`. If you
 need books prefetched to authors_by_age, then doing
 `.prefetch_related('authors', to_attr='authors_by_age',
 queryset=Author.objects.order_by('age').prefetch_related('books'))` should
 work.

 The prefetch happens directly into a list. That is,
 obj.authors_by_age.filter(...) doesn't work. The obj.authors_by_age
 attribute is a list instance, containing the related objects. Not creating
 a QueyrSet for each obj is a big performance optimization (IIRC around 5x
 performance difference when fetching small amount of related objects in a
 large queryset). Fetching directly into a list should also make the
 implementation cleaner.

 For the first implementation making sure fetching basic querysets works
 well should be enough. For example, if it turns out it will be hard to
 support prefetching values() querysets or generic relations, then throwing
 an error and documenting what doesn't work seems good enough.

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Re: [Django] #17001: Allow usage of custom querysets in prefetch_related

[Django]

#17001: Allow usage of custom querysets in prefetch_related
-+-
 Reporter:  akaariai |Owner:  nobody
 Type:  New feature  |   Status:  new
Component:  Database layer   |  Version:  1.3
  (models, ORM)  |   Resolution:
 Severity:  Normal   | Triage Stage:  Accepted
 Keywords:  prefetch_related |  Needs documentation:  1
Has patch:  1|  Patch needs improvement:  1
  Needs tests:  1|UI/UX:  0
Easy pickings:  0|
-+-

Comment (by mjtamlyn):

 ML discussion on proposed alternative API:
 https://groups.google.com/forum/?fromgroups=#!topic/django-
 developers/BSyGOR7cMEs

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Re: [Django] #17001: Allow usage of custom querysets in prefetch_related

[Django]

#17001: Allow usage of custom querysets in prefetch_related
-+-
 Reporter:  akaariai |Owner:  nobody
 Type:  New feature  |   Status:  new
Component:  Database layer   |  Version:  1.3
  (models, ORM)  |   Resolution:
 Severity:  Normal   | Triage Stage:  Accepted
 Keywords:  prefetch_related |  Needs documentation:  1
Has patch:  1|  Patch needs improvement:  1
  Needs tests:  1|UI/UX:  0
Easy pickings:  0|
-+-

Comment (by akaariai):

 Note that this ticket is totally dependant on finding a good API. The
 functionality was already implemented using R() objects, the problem is
 that the API wasn't usable enough for merge. So, find a nice API and it is
 very likely that this feature will be merged.

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Re: [Django] #17001: Allow usage of custom querysets in prefetch_related

[Django]

#17001: Allow usage of custom querysets in prefetch_related
-+-
 Reporter:  akaariai |Owner:  nobody
 Type:  New feature  |   Status:  new
Component:  Database layer   |  Version:  1.3
  (models, ORM)  |   Resolution:
 Severity:  Normal   | Triage Stage:  Accepted
 Keywords:  prefetch_related |  Needs documentation:  1
Has patch:  1|  Patch needs improvement:  1
  Needs tests:  1|UI/UX:  0
Easy pickings:  0|
-+-

Comment (by aaugustin):

 The tone of your comment highlight everything that is wrong with the
 consumer approach to open-source :)

 If this issue bothers you so much, why don't you put your energy into
 resolving it rather than angry comments?

 Seriously — your comment makes me *less* likely to contribute to this
 issue; I don't feel like helping someone who shouts on volunteers.

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Re: [Django] #17001: Allow usage of custom querysets in prefetch_related

[Django]

#17001: Allow usage of custom querysets in prefetch_related
-+-
 Reporter:  akaariai |Owner:  nobody
 Type:  New feature  |   Status:  new
Component:  Database layer   |  Version:  1.3
  (models, ORM)  |   Resolution:
 Severity:  Normal   | Triage Stage:  Accepted
 Keywords:  prefetch_related |  Needs documentation:  1
Has patch:  1|  Patch needs improvement:  1
  Needs tests:  1|UI/UX:  0
Easy pickings:  0|
-+-

Comment (by chokosabe@…):

 The status of this ticket highlights everything that is wrong with how
 Django is being developed currently. 22 months! and still no movement on
 this!!!

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Re: [Django] #17001: Allow usage of custom querysets in prefetch_related

[Django]

#17001: Allow usage of custom querysets in prefetch_related
-+-
 Reporter:  akaariai |Owner:  nobody
 Type:  New feature  |   Status:  new
Component:  Database layer   |  Version:  1.3
  (models, ORM)  |   Resolution:
 Severity:  Normal   | Triage Stage:  Accepted
 Keywords:  prefetch_related |  Needs documentation:  1
Has patch:  1|  Patch needs improvement:  1
  Needs tests:  1|UI/UX:  0
Easy pickings:  0|
-+-
Changes (by ethan.jucovy@…):

 * cc: ethan.jucovy@… (added)


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Re: [Django] #17001: Allow usage of custom querysets in prefetch_related

[Django]

#17001: Allow usage of custom querysets in prefetch_related
-+-
 Reporter:  akaariai |Owner:  nobody
 Type:  New feature  |   Status:  new
Component:  Database layer   |  Version:  1.3
  (models, ORM)  |   Resolution:
 Severity:  Normal   | Triage Stage:  Accepted
 Keywords:  prefetch_related |  Needs documentation:  1
Has patch:  1|  Patch needs improvement:  1
  Needs tests:  1|UI/UX:  0
Easy pickings:  0|
-+-
Changes (by elektrrrus):

 * cc: k.sikora@… (added)


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Re: [Django] #17001: Allow usage of custom querysets in prefetch_related

[Django]

#17001: Allow usage of custom querysets in prefetch_related
-+-
 Reporter:  akaariai |Owner:  nobody
 Type:  New feature  |   Status:  new
Component:  Database layer   |  Version:  1.3
  (models, ORM)  |   Resolution:
 Severity:  Normal   | Triage Stage:  Accepted
 Keywords:  prefetch_related |  Needs documentation:  1
Has patch:  1|  Patch needs improvement:  1
  Needs tests:  1|UI/UX:  0
Easy pickings:  0|
-+-

Comment (by aaugustin):

 The current status of this feature is fully and accurately reflected in
 the description above.

 There's a patch, but it needs improvements, tests, and documentation.

 Since it's a fairly large and complex feature, gaining the support of a
 core developer will be critical to complete the patch and have it
 committed.

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Re: [Django] #17001: Allow usage of custom querysets in prefetch_related

[Django]

#17001: Allow usage of custom querysets in prefetch_related
-+-
 Reporter:  akaariai |Owner:  nobody
 Type:  New feature  |   Status:  new
Component:  Database layer   |  Version:  1.3
  (models, ORM)  |   Resolution:
 Severity:  Normal   | Triage Stage:  Accepted
 Keywords:  prefetch_related |  Needs documentation:  1
Has patch:  1|  Patch needs improvement:  1
  Needs tests:  1|UI/UX:  0
Easy pickings:  0|
-+-

Comment (by anonymous):

 It would be a life saver for me! What is the status of this feature?

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Re: [Django] #17001: Allow usage of custom querysets in prefetch_related

[Django]

#17001: Allow usage of custom querysets in prefetch_related
-+-
 Reporter:  akaariai |Owner:  nobody
 Type:  New feature  |   Status:  new
Component:  Database layer   |  Version:  1.3
  (models, ORM)  |   Resolution:
 Severity:  Normal   | Triage Stage:  Accepted
 Keywords:  prefetch_related |  Needs documentation:  1
Has patch:  1|  Patch needs improvement:  1
  Needs tests:  1|UI/UX:  0
Easy pickings:  0|
-+-

Comment (by naktinis@…):

 Would be great to have this! What is the status of this feature request
 currently?

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Re: [Django] #17001: Allow usage of custom querysets in prefetch_related

[Django]

#17001: Allow usage of custom querysets in prefetch_related
-+-
 Reporter:  akaariai |Owner:  nobody
 Type:  New feature  |   Status:  new
Component:  Database layer   |  Version:  1.3
  (models, ORM)  |   Resolution:
 Severity:  Normal   | Triage Stage:  Accepted
 Keywords:  prefetch_related |  Needs documentation:  1
Has patch:  1|  Patch needs improvement:  1
  Needs tests:  1|UI/UX:  0
Easy pickings:  0|
-+-
Changes (by AndrewIngram):

 * cc: AndrewIngram (added)


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Re: [Django] #17001: Allow usage of custom querysets in prefetch_related

[Django]

#17001: Allow usage of custom querysets in prefetch_related
-+-
 Reporter:  akaariai |Owner:  nobody
 Type:  New feature  |   Status:  new
Component:  Database layer   |  Version:  1.3
  (models, ORM)  |   Resolution:
 Severity:  Normal   | Triage Stage:  Accepted
 Keywords:  prefetch_related |  Needs documentation:  1
Has patch:  1|  Patch needs improvement:  1
  Needs tests:  1|UI/UX:  0
Easy pickings:  0|
-+-

Comment (by ebertti@…):

 Great feature!!! I will love this!!!

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Re: [Django] #17001: Allow usage of custom querysets in prefetch_related

[Django]

#17001: Allow usage of custom querysets in prefetch_related
-+-
 Reporter:  akaariai |Owner:  nobody
 Type:  New feature  |   Status:  new
Component:  Database layer   |  Version:  1.3
  (models, ORM)  |   Resolution:
 Severity:  Normal   | Triage Stage:  Accepted
 Keywords:  prefetch_related |  Needs documentation:  1
Has patch:  1|  Patch needs improvement:  1
  Needs tests:  1|UI/UX:  0
Easy pickings:  0|
-+-

Comment (by anonymous):

 Pretty neat stuff!

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Re: [Django] #17001: Allow usage of custom querysets in prefetch_related

[Django]

#17001: Allow usage of custom querysets in prefetch_related
-+-
 Reporter:  akaariai |Owner:  nobody
 Type:  New feature  |   Status:  new
Component:  Database layer   |  Version:  1.3
  (models, ORM)  |   Resolution:
 Severity:  Normal   | Triage Stage:  Accepted
 Keywords:  prefetch_related |  Needs documentation:  1
Has patch:  1|  Patch needs improvement:  1
  Needs tests:  1|UI/UX:  0
Easy pickings:  0|
-+-
Changes (by mjtamlyn):

 * cc: marc.tamlyn@… (added)
 * needs_better_patch:  0 => 1
 * needs_tests:  0 => 1


Comment:

 I would love this feature!

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Re: [Django] #17001: Allow usage of custom querysets in prefetch_related

[Django]

#17001: Allow usage of custom querysets in prefetch_related
-+-
 Reporter:  akaariai |Owner:  nobody
 Type:  New feature  |   Status:  new
Component:  Database layer   |  Version:  1.3
  (models, ORM)  |   Resolution:
 Severity:  Normal   | Triage Stage:  Accepted
 Keywords:  prefetch_related |  Needs documentation:  1
Has patch:  1|  Patch needs improvement:  0
  Needs tests:  0|UI/UX:  0
Easy pickings:  0|
-+-

Comment (by akaariai):

 If I recall correctly it is there so you can't shadow an existing
 queryset. This patch will fetch the results as a list, not as a queryset
 when you use a custom qs. So, if you use custom qs to fetch authors for
 book, then book.authors.all() wouldn't work, the items would be in
 book.authors, and book.authors would be a list.

 In general, we want this feature in Django, but the current API isn't
 something wanted in Django...

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Re: [Django] #17001: Allow usage of custom querysets in prefetch_related

[Django]

#17001: Allow usage of custom querysets in prefetch_related
-+-
 Reporter:  akaariai |Owner:  nobody
 Type:  New feature  |   Status:  new
Component:  Database layer   |  Version:  1.3
  (models, ORM)  |   Resolution:
 Severity:  Normal   | Triage Stage:  Accepted
 Keywords:  prefetch_related |  Needs documentation:  1
Has patch:  1|  Patch needs improvement:  0
  Needs tests:  0|UI/UX:  0
Easy pickings:  0|
-+-

Comment (by iu_long):

 What is the reasoning behind this in the R object's __init__ ?

 {{{
 if qs is not None and not to_attr:
   raise ValueError('When custom qs is defined, to_attr '
   'must also be defined')

 }}}

 In my use case, I really need the custom prefetch to go on the same
 attribute and this prevents me from doing so.
 Does not having a 'to_attr' with queryset break something or it is just
 for safety ( preventing accidents )?

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Re: [Django] #17001: Allow usage of custom querysets in prefetch_related

[Django]

#17001: Allow usage of custom querysets in prefetch_related
-+-
 Reporter:  akaariai |Owner:  nobody
 Type:  New feature  |   Status:  new
Component:  Database layer   |  Version:  1.3
  (models, ORM)  |   Resolution:
 Severity:  Normal   | Triage Stage:  Accepted
 Keywords:  prefetch_related |  Needs documentation:  1
Has patch:  1|  Patch needs improvement:  0
  Needs tests:  0|UI/UX:  0
Easy pickings:  0|
-+-

Comment (by Kronuz):

 I added an update for django 1.4 (tests still need to be upgraded)
 ...however, the question I still have is, the added attribute (to_attr) is
 a list, and I suppose it should be/act as a `QuerySet` instead, in my most
 humble opinion.

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Re: [Django] #17001: Allow usage of custom querysets in prefetch_related

[Django]

#17001: Allow usage of custom querysets in prefetch_related
-+-
 Reporter:  akaariai |Owner:  nobody
 Type:  New feature  |   Status:  new
Component:  Database layer   |  Version:  1.3
  (models, ORM)  |   Resolution:
 Severity:  Normal   | Triage Stage:  Accepted
 Keywords:  prefetch_related |  Needs documentation:  1
Has patch:  1|  Patch needs improvement:  0
  Needs tests:  0|UI/UX:  0
Easy pickings:  0|
-+-
Changes (by lukeplant):

 * stage:  Unreviewed => Accepted


Comment:

 @akaariai:

 Accepted on the basis that the feature in general would be nice.

 However, I haven't looked at the code at all. I doubt that I will have
 time to look at this before 1.4 is released. Part of me would actually
 like to leave the current version of `prefetch_related()` to get some
 testing in the wild before we build on top of it.

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Re: [Django] #17001: Allow usage of custom querysets in prefetch_related

[Django]

#17001: Allow usage of custom querysets in prefetch_related
-+-
 Reporter:  akaariai |Owner:  nobody
 Type:  New feature  |   Status:  new
Component:  Database layer   |  Version:  1.3
  (models, ORM)  |   Resolution:
 Severity:  Normal   | Triage Stage:
 Keywords:  prefetch_related |  Unreviewed
Has patch:  1|  Needs documentation:  1
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-
Changes (by akaariai):

 * needs_better_patch:   => 0
 * has_patch:  0 => 1
 * needs_tests:   => 0
 * needs_docs:   => 1


Comment:

 Ok, I think I have a ready patch for this. There are some TODO comments
 still there (a part of them are personal TODOs, some are real TODOs). And
 this still needs documentation.

 About the documentation, I don't know if we should mention that it is
 possible to chain prefetches in this manner:
 {{{
 qs = SomeModel.objects.prefetch_related(
R('rel_model', qs=RelModel.objects.order_by('-pk'), to_attr='foo_lst'),
R('foo_lst__another_model', qs=AnotModel.objects.order_by('-pk'),
 to_attr='anot_lst')
 )
 }}}

 The problem is that it is really, really, easy to do this instead:
 {{{
 qs = SomeModel.objects.prefetch_related(
R('rel_model', qs=RelModel.objects.order_by('-pk'), to_attr='foo_lst'),
R('ref_model__another_model', qs=AnotModel.objects.order_by('-pk'),
 to_attr='anot_lst')
 )
 }}}

 Note that the lookup path in the second R-object isn't referring to
 foo_lst, but instead ref_model, so we will fetch the ref_models another
 time. I would even go so far as to explicitly prohibit the
 foo_lst`__`another_model usage, as it is confusing as hell.

 Chaining prefetches can be done by using custom querysets which have
 prefetches. The only problem is that if you get a queryset which already
 has prefetches, you can't chain to the existing ones. One idea is to have
 a 'name' and 'chain_to' kwargs for R objects, and then you could chain by
 the name.

 My suggestion is that lets leave this for 1.5. I would explicitly prohibit
 the foo_lst`__`another_model way of chaining. It can be resurrected if
 need be. Then there is still the usual naming issues.

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[Django] #17001: Allow usage of custom querysets in prefetch_related

[Django]

#17001: Allow usage of custom querysets in prefetch_related
--+
 Reporter:  akaariai  |  Owner:  nobody
 Type:  New feature   | Status:  new
Component:  Database layer (models, ORM)  |Version:  1.3
 Severity:  Normal|   Keywords:
 Triage Stage:  Unreviewed|  prefetch_related
Easy pickings:  0 |  Has patch:  0
  |  UI/UX:  0
--+
 #16973 introduced prefetch_related. I would like to extend it so that one
 can use custom querysets for the fetching. This also requires the ability
 to define the attribute name to use for the prefetched objects, as it is
 not valid to return filtered objects from related_manager.all(). There is
 also the possibility that one wants to fetch multiple objects of the same
 type with prefetch_related (young authors to one attribute, old authors to
 another).

 The proposed API is following:
 {{{
 # The normal usage does not change
 SomeModel.objects.prefetch_related('rel_model', 'rel_model__another_rel')
 # You can pass R objects to prefetch_related
 # The syntax for R is
 # R(lookup_path, to_attr=None, qs=None)
 # Thus:
 SomeModel.objects.prefetch_related(R('rel_model'),
 R('rel_model__another_rel'))
 # is equivalent to the first call.
 # One can use to_attr alone:
 SomeModel.objects.prefetch_related(R('rel_model', to_attr='foo_lst'), ...)
 # custom queryset
 SomeModel.objects.prefetch_related(
 R('rel_model', to_attr='foo_lst',
 qs=RelModel.objects.order_by('foo')),
 ...
 )
 # If qs is defined, to_attr must be defined also:
 SomeModel.objects.prefetch_related(R('rel_model',
 qs=RelModel.objects.order_by('-pk')))
 -> Error: Thou shalt not use qs without to_attr
 # One can use the to_attr in nested calls:
 qs = SomeModel.objects.prefetch_related(
R('rel_model', qs=RelModel.objects.order_by('-pk'), to_attr='foo_lst'),
R('foo_lst__another_model', qs=AnotModel.objects.order_by('-pk'),
 to_attr='anot_lst')
 )
 # This will result in every object O in foo_lst to have attribute anot_lst
 containing
 # related objects to O, fetched from the above given qs.
 # Going still deeper would need to use syntax:
 qs = qs.prefetch_related(
R('foo_lst__anot_lst__third_model',
 qs=ThirdModel.objects.order_by('-pk'), to_attr='bar_lst'),
 )
 }}}

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