Re: [Django] #22268: values_list() on a ManyToManyField returns extra None's when iterated over.

[Django]

#22268: values_list() on a ManyToManyField returns extra None's when iterated 
over.
-+-
 Reporter:  k_sze|Owner:
 Type:   |  anubhav9042
  Cleanup/optimization   |   Status:  assigned
Component:  Documentation|  Version:  master
 Severity:  Normal   |   Resolution:
 Keywords:  orm, values_list,| Triage Stage:  Accepted
  ManyToManyField|  Needs documentation:  0
Has patch:  0|  Patch needs improvement:  0
  Needs tests:  0|UI/UX:  0
Easy pickings:  0|
-+-
Changes (by timo):

 * type:  Bug => Cleanup/optimization
 * component:  Database layer (models, ORM) => Documentation


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Re: [Django] #22268: values_list() on a ManyToManyField returns extra None's when iterated over.

[Django]

#22268: values_list() on a ManyToManyField returns extra None's when iterated 
over.
-+-
 Reporter:  k_sze|Owner:
 Type:  Bug  |  anubhav9042
Component:  Database layer   |   Status:  assigned
  (models, ORM)  |  Version:  master
 Severity:  Normal   |   Resolution:
 Keywords:  orm, values_list,| Triage Stage:  Accepted
  ManyToManyField|  Needs documentation:  0
Has patch:  0|  Patch needs improvement:  0
  Needs tests:  0|UI/UX:  0
Easy pickings:  0|
-+-

Comment (by anubhav9042):

 As discussed on IRC and mailing list, the solution has come out to be a
 doc update for this behaviour rather than tweaking the code any further.

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Re: [Django] #22268: values_list() on a ManyToManyField returns extra None's when iterated over.

[Django]

#22268: values_list() on a ManyToManyField returns extra None's when iterated 
over.
-+-
 Reporter:  k_sze|Owner:
 Type:  Bug  |  anubhav9042
Component:  Database layer   |   Status:  assigned
  (models, ORM)  |  Version:  master
 Severity:  Normal   |   Resolution:
 Keywords:  orm, values_list,| Triage Stage:  Accepted
  ManyToManyField|  Needs documentation:  0
Has patch:  0|  Patch needs improvement:  0
  Needs tests:  0|UI/UX:  0
Easy pickings:  0|
-+-

Comment (by anubhav9042):

 For better discussion, I have opened a thread:
 https://groups.google.com/forum/#!topic/django-developers/DAslY6GI1O8

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Re: [Django] #22268: values_list() on a ManyToManyField returns extra None's when iterated over.

[Django]

#22268: values_list() on a ManyToManyField returns extra None's when iterated 
over.
-+-
 Reporter:  k_sze|Owner:
 Type:  Bug  |  anubhav9042
Component:  Database layer   |   Status:  assigned
  (models, ORM)  |  Version:  master
 Severity:  Normal   |   Resolution:
 Keywords:  orm, values_list,| Triage Stage:  Accepted
  ManyToManyField|  Needs documentation:  0
Has patch:  0|  Patch needs improvement:  0
  Needs tests:  0|UI/UX:  0
Easy pickings:  0|
-+-

Comment (by k_sze):

 Replying to [comment:26 anubhav9042]:
 > > In the end, the subclassed `dict` and `tuple` would work somewhat like
 the Django model, except that you access things in the form of
 dictionaries and tuples, and you limit the elements that can appear in
 them.
 >
 > Will think
 > Although the same difficulty might come here as well.
 My idea is for these subclassed `dict` and `tuple` to be used recursively.
 And then because they are constructed lazily using QuerySets, you won't
 get combinatorial explosions, so you won't have to do any clubbing.

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Re: [Django] #22268: values_list() on a ManyToManyField returns extra None's when iterated over.

[Django]

#22268: values_list() on a ManyToManyField returns extra None's when iterated 
over.
-+-
 Reporter:  k_sze|Owner:
 Type:  Bug  |  anubhav9042
Component:  Database layer   |   Status:  assigned
  (models, ORM)  |  Version:  master
 Severity:  Normal   |   Resolution:
 Keywords:  orm, values_list,| Triage Stage:  Accepted
  ManyToManyField|  Needs documentation:  0
Has patch:  0|  Patch needs improvement:  0
  Needs tests:  0|UI/UX:  0
Easy pickings:  0|
-+-

Comment (by anubhav9042):

 > In the end, the subclassed `dict` and `tuple` would work somewhat like
 the Django model, except that you access things in the form of
 dictionaries and tuples, and you limit the elements that can appear in
 them.

 Will think
 Although the same difficulty might come here as well.

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Re: [Django] #22268: values_list() on a ManyToManyField returns extra None's when iterated over.

[Django]

#22268: values_list() on a ManyToManyField returns extra None's when iterated 
over.
-+-
 Reporter:  k_sze|Owner:
 Type:  Bug  |  anubhav9042
Component:  Database layer   |   Status:  assigned
  (models, ORM)  |  Version:  master
 Severity:  Normal   |   Resolution:
 Keywords:  orm, values_list,| Triage Stage:  Accepted
  ManyToManyField|  Needs documentation:  0
Has patch:  0|  Patch needs improvement:  0
  Needs tests:  0|UI/UX:  0
Easy pickings:  0|
-+-

Comment (by anubhav9042):

 > Although I have another idea in mind:
 > We just add `pk` to the query and then when final result is obtained we
 can club the dicts/tuples having same `pk` and remove `pk`.
 >
 > Thoughts??
 >
 > I am suggesting changes this way becoz I think that the query generated
 is correct.

 I tried to do this way, but clubbing those dics/tuples is not easy as they
 are not exactly dics/tuple rather QuerySets.
 Will keep trying and post back soon

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Re: [Django] #22268: values_list() on a ManyToManyField returns extra None's when iterated over.

[Django]

#22268: values_list() on a ManyToManyField returns extra None's when iterated 
over.
-+-
 Reporter:  k_sze|Owner:
 Type:  Bug  |  anubhav9042
Component:  Database layer   |   Status:  assigned
  (models, ORM)  |  Version:  master
 Severity:  Normal   |   Resolution:
 Keywords:  orm, values_list,| Triage Stage:  Accepted
  ManyToManyField|  Needs documentation:  0
Has patch:  0|  Patch needs improvement:  0
  Needs tests:  0|UI/UX:  0
Easy pickings:  0|
-+-

Comment (by k_sze):

 Another idea that I have, which is probably crazy:

 Instead of retrieving the M2M or reverse foreign key values in the same
 SQL query, use a clever combination of:
 * `prefetch_related()`
 * subclassing `dict` and `tuple`

 So `values()` and `values_list` return these subclassed dicts and tuples,
 which lazily construct and return the relevant M2M or reverse foreign key
 elements when they are accessed.

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Re: [Django] #22268: values_list() on a ManyToManyField returns extra None's when iterated over.

[Django]

#22268: values_list() on a ManyToManyField returns extra None's when iterated 
over.
-+-
 Reporter:  k_sze|Owner:
 Type:  Bug  |  anubhav9042
Component:  Database layer   |   Status:  assigned
  (models, ORM)  |  Version:  master
 Severity:  Normal   |   Resolution:
 Keywords:  orm, values_list,| Triage Stage:  Accepted
  ManyToManyField|  Needs documentation:  0
Has patch:  0|  Patch needs improvement:  0
  Needs tests:  0|UI/UX:  0
Easy pickings:  0|
-+-

Comment (by k_sze):

 Replying to [comment:22 anubhav9042]:
 > Although I have another idea in mind:
 > We just add `pk` to the query and then when final result is obtained we
 can club the dicts/tuples having same `pk` and remove `pk`.
 >
 > Thoughts??
 >
 > I am suggesting changes this way becoz I think that the query generated
 is correct.
 And also remove the ones where the `pk` is `None` (due to the LEFT OUTER
 JOIN)?

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Re: [Django] #22268: values_list() on a ManyToManyField returns extra None's when iterated over.

[Django]

#22268: values_list() on a ManyToManyField returns extra None's when iterated 
over.
-+-
 Reporter:  k_sze|Owner:
 Type:  Bug  |  anubhav9042
Component:  Database layer   |   Status:  assigned
  (models, ORM)  |  Version:  master
 Severity:  Normal   |   Resolution:
 Keywords:  orm, values_list,| Triage Stage:  Accepted
  ManyToManyField|  Needs documentation:  0
Has patch:  0|  Patch needs improvement:  0
  Needs tests:  0|UI/UX:  0
Easy pickings:  0|
-+-

Comment (by anubhav9042):

 Although I have another idea in mind:
 We just add `pk` to the query and then when final result is obtained we
 can club the dicts/tuples having same `pk` and remove `pk`.

 Thoughts??

 I am suggesting changes this way becoz I think that the query generated is
 correct.

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Ticket URL: 
Django 
The Web framework for perfectionists with deadlines.

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Re: [Django] #22268: values_list() on a ManyToManyField returns extra None's when iterated over.

[Django]

#22268: values_list() on a ManyToManyField returns extra None's when iterated 
over.
-+-
 Reporter:  k_sze|Owner:
 Type:  Bug  |  anubhav9042
Component:  Database layer   |   Status:  assigned
  (models, ORM)  |  Version:  master
 Severity:  Normal   |   Resolution:
 Keywords:  orm, values_list,| Triage Stage:  Accepted
  ManyToManyField|  Needs documentation:  0
Has patch:  0|  Patch needs improvement:  0
  Needs tests:  0|UI/UX:  0
Easy pickings:  0|
-+-

Comment (by anubhav9042):

 Replying to [comment:19 k_sze]:
 > I would argue against solving the problem this way.
 >
 > 1. Letting the number of results grow combinatorially seems
 questionable. According to the current documentation for `values()` and
 `values_list()`, each result is supposed to correspond to ''one'' model
 object. Granted, the documentation doesn't say that the query cannot
 return multiple results for each model object, it still feels wrong
 because, in the current behaviour, none of the results represents a
 coherent ''big picture'' of ''one'' model object; for each model object,
 the values are either getting duplicated or fragmented across multiple
 dictionaries or tuples.
 > 2. I suspect that including the `id` (or `pk`) still doesn't solve the
 ambiguity that arises when you query for a nullable field of an M2M field
 (e.g. `students__year_of_birth`). You still get `None` for both a) null
 `year_of_birth` or b) no student at all. I can't confirm this yet because
 the diff doesn't seem to work against Django 1.6.2 (what version does the
 diff target?).
 >
 > By the way, the problem is not limited to M2M fields, but also to
 ForeignKeys; e.g. if you have a `Province` model and a `City` model, and
 the `City` has a `ForeignKey` on `Province`, and you do
 `Province.objects.values('cities')`, you get the same problem.
 >
 > This is looking like a rabbit hole. :(


 Diff targets master.
 Even if two `None`s are returned from `pk` value we know that which
 corresponds to what. What should we give instead of `None`

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Re: [Django] #22268: values_list() on a ManyToManyField returns extra None's when iterated over.

[Django]

#22268: values_list() on a ManyToManyField returns extra None's when iterated 
over.
-+-
 Reporter:  k_sze|Owner:
 Type:  Bug  |  anubhav9042
Component:  Database layer   |   Status:  assigned
  (models, ORM)  |  Version:  master
 Severity:  Normal   |   Resolution:
 Keywords:  orm, values_list,| Triage Stage:  Accepted
  ManyToManyField|  Needs documentation:  0
Has patch:  0|  Patch needs improvement:  0
  Needs tests:  0|UI/UX:  0
Easy pickings:  0|
-+-

Comment (by erikr):

 The examples in comment:15 and comment:16 do seem odd. However, have a
 close look at #5768, where this behaviour seems to have been added. I
 haven't read it in detail, but there may be some explanation in there of
 the choices made.

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Re: [Django] #22268: values_list() on a ManyToManyField returns extra None's when iterated over.

[Django]

#22268: values_list() on a ManyToManyField returns extra None's when iterated 
over.
-+-
 Reporter:  k_sze|Owner:
 Type:  Bug  |  anubhav9042
Component:  Database layer   |   Status:  assigned
  (models, ORM)  |  Version:  master
 Severity:  Normal   |   Resolution:
 Keywords:  orm, values_list,| Triage Stage:  Accepted
  ManyToManyField|  Needs documentation:  0
Has patch:  0|  Patch needs improvement:  0
  Needs tests:  0|UI/UX:  0
Easy pickings:  0|
-+-

Comment (by k_sze):

 I would argue against solving the problem this way.

 1. Letting the number of results grow combinatorially seems questionable.
 According to the current documentation for `values()` and `values_list()`,
 each result is supposed to correspond to ''one'' model object. Granted,
 the documentation doesn't say that the query cannot return multiple
 results for each model object, it still feels wrong because, in the
 current behaviour, none of the results represents a coherent ''big
 picture'' of ''one'' model object; for each model object, the values are
 either getting duplicated or fragmented across multiple dictionaries or
 tuples.
 2. I suspect that including the `id` (or `pk`) still doesn't solve the
 ambiguity that arises when you query for a nullable field of an M2M field
 (e.g. `students__year_of_birth`). You still get `None` for both a) null
 `year_of_birth` or b) no student at all. I can't confirm this yet because
 the diff doesn't seem to work against Django 1.6.2 (what version does the
 diff target?).

 By the way, the problem is not limited to M2M fields, but also to
 ForeignKeys; e.g. if you have a `Province` model and a `City` model, and
 the `City` has a `ForeignKey` on `Province`, and you do
 `Province.objects.values('cities')`, you get the same problem.

 This is looking like a rabbit hole. :(

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Re: [Django] #22268: values_list() on a ManyToManyField returns extra None's when iterated over.

[Django]

#22268: values_list() on a ManyToManyField returns extra None's when iterated 
over.
-+-
 Reporter:  k_sze|Owner:
 Type:  Bug  |  anubhav9042
Component:  Database layer   |   Status:  assigned
  (models, ORM)  |  Version:  master
 Severity:  Normal   |   Resolution:
 Keywords:  orm, values_list,| Triage Stage:  Accepted
  ManyToManyField|  Needs documentation:  0
Has patch:  0|  Patch needs improvement:  0
  Needs tests:  0|UI/UX:  0
Easy pickings:  0|
-+-

Comment (by anubhav9042):

 In the diff, the added lines are in red color..

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Re: [Django] #22268: values_list() on a ManyToManyField returns extra None's when iterated over.

[Django]

#22268: values_list() on a ManyToManyField returns extra None's when iterated 
over.
-+-
 Reporter:  k_sze|Owner:
 Type:  Bug  |  anubhav9042
Component:  Database layer   |   Status:  assigned
  (models, ORM)  |  Version:  master
 Severity:  Normal   |   Resolution:
 Keywords:  orm, values_list,| Triage Stage:  Accepted
  ManyToManyField|  Needs documentation:  0
Has patch:  0|  Patch needs improvement:  0
  Needs tests:  0|UI/UX:  0
Easy pickings:  0|
-+-

Comment (by anubhav9042):

 According to me the query generated for
 {{{Class.objects.values('available_in_languages', 'students')}}}:
 {{{
 SELECT `tic_22268_class_available_in_languages`.`language_id`,
 `tic_22268_class_students`.`student_id` FROM `tic_22268_class` LEFT OUTER
 JOIN `tic_22268_class_available_in_languages` ON (`tic_22268_class`.`id` =
 `tic_22268_class_available_in_languages`.`class_id`) LEFT OUTER JOIN
 `tic_22268_class_students` ON (`tic_22268_class`.`id` =
 `tic_22268_class_students`.`class_id`)
 }}}

 is correct as it yield the following result
 {{{
 language_id student_id
 NULL   1
 NULL   NULL
 1  1
 1  2
 2  1
 2  2
 }}}

 Although the result is correct as we want combination of
 `available_in_languages` and `students` for `Class` objects. However it is
 confusing.
 I propose the following:
 Whenever there is a case of M2M in values() or values_list(), we could
 introduce additional `id` into the query, which will help in making the
 result meaningful and understandable.

 We make the query into:
 {{{
 SELECT `tic_22268_class_available_in_languages`.`language_id`,
 `tic_22268_class_students`.`student_id`, `tic_22268_class_students`.`id`
 FROM `tic_22268_class` LEFT OUTER JOIN
 `tic_22268_class_available_in_languages` ON (`tic_22268_class`.`id` =
 `tic_22268_class_available_in_languages`.`class_id`) LEFT OUTER JOIN
 `tic_22268_class_students` ON (`tic_22268_class`.`id` =
 `tic_22268_class_students`.`class_id`)
 }}}

 resulting in
 {{{
 language_id student_id  id
 NULL  1  1
 NULL   NULL NULL
 1 1 2
 1 2 3
 2 1 2
 2 2 3
 }}}

 The output also becomes:
 {{{
 [{'students': 1L, 'available_in_languages': None, 'id': 1L},
 {'students': None, 'available_in_languages': None, 'id': 2L},
 {'students': 1L, 'available_in_languages': 1L, 'id': 3L}, {'students': 2L,
 'available_in_languages': 1L, 'id': 3L}, {
 'students': 1L, 'available_in_languages': 2L, 'id': 3L}, {'students': 2L,
 'available_in_languages': 2L, 'id': 3L}]
 }}}
 }}}

 Now the result is as required, since we wanted the combination of values:
 'available_in_languages' and 'students' along with 'id' of the `Class`
 object to which it belongs.

 I am adding a diff.

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Re: [Django] #22268: values_list() on a ManyToManyField returns extra None's when iterated over.

[Django]

#22268: values_list() on a ManyToManyField returns extra None's when iterated 
over.
-+-
 Reporter:  k_sze|Owner:
 Type:  Bug  |  anubhav9042
Component:  Database layer   |   Status:  assigned
  (models, ORM)  |  Version:  master
 Severity:  Normal   |   Resolution:
 Keywords:  orm, values_list,| Triage Stage:  Accepted
  ManyToManyField|  Needs documentation:  0
Has patch:  0|  Patch needs improvement:  0
  Needs tests:  0|UI/UX:  0
Easy pickings:  0|
-+-

Comment (by k_sze):

 To demonstrate how bad things become once you have multiple M2M fields, I
 created a new `Language` model and add it as a M2M field in the Class
 model:
 {{{
 from django.db import models

 # other Model definitions skipped ...

 class Class(models.Model):
 school = models.ForeignKey(School)
 name = models.CharField(unique=True, max_length=255)
 students = models.ManyToManyField('Student')
 available_in_languages = models.ManyToManyField('Language')


 class Language(models.Model):
 name = models.CharField(max_length=255)
 }}}

 Now I create new languages and add them to the Discrete Mathematics class
 (which now has 2 students, if you recall):
 {{{
 # French
 >>> french = Language(name='French')
 >>> french.save()

 # English
 >>> english = Language(name='English')
 >>> english.save()

 # Add them to Discrete Mathematics class
 discrete_math = Class.objects.get(name='Discrete Mathematics')
 discrete_math.available_in_languages.add(french)
 discrete_math.available_in_languages.add(english)
 }}}

 Now I make a `values()` query:
 {{{
 >>> Class.objects.values('available_in_languages', 'students')
 [{'students': 1, 'available_in_languages': None}, {'students': None,
 'available_in_languages': None}, {'students': 1, 'available_in_languages':
 2}, {'students': 2, 'available_in_languages': 2}, {'students': 1,
 'available_in_languages': 1}, {'students': 2, 'available_in_languages':
 1}]
 }}}
 That's 6 dictionaries now!

 Similarly, with `values_list()`:
 {{{
 >>> Class.objects.values_list('available_in_languages', 'students')
 [(None, 1), (None, None), (2, 1), (2, 2), (1, 1), (1, 2)]
 }}}
 6 tuples even though we only have 3 Class objects.

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Re: [Django] #22268: values_list() on a ManyToManyField returns extra None's when iterated over.

[Django]

#22268: values_list() on a ManyToManyField returns extra None's when iterated 
over.
-+-
 Reporter:  k_sze|Owner:
 Type:  Bug  |  anubhav9042
Component:  Database layer   |   Status:  assigned
  (models, ORM)  |  Version:  master
 Severity:  Normal   |   Resolution:
 Keywords:  orm, values_list,| Triage Stage:  Accepted
  ManyToManyField|  Needs documentation:  0
Has patch:  0|  Patch needs improvement:  0
  Needs tests:  0|UI/UX:  0
Easy pickings:  0|
-+-

Comment (by k_sze):

 Actually the whole behaviour of `values()` and `values_list()` seems to be
 wrong once you mix M2M fields into the picture. I just tried creating more
 Class and Student objects:

 {{{
 # New student, Joe Blo
 >>> joe_blo = Student(surname='Blo', given_name='Joe')
 >>> joe_blo.save()

 # New class, Discrete Mathematics
 >>> discrete_math = Class(name='Discrete Mathematics', school=concordia)
 >>> discrete_math.save()

 # Enroll both john_smith and joe_blo in discrete_math
 discrete_math.students.add(joe_blo)
 discrete_math.students.add(john_smith)
 }}}

 First, let's look at `values()` queries:
 {{{
 >>> Class.objects.values()
 [{u'id': 1, 'name': u'Software Engineering', 'school_id': 1}, {u'id': 2,
 'name': u'Computer Engineering', 'school_id': 1}, {u'id': 4, 'name':
 u'Discrete Mathematics', 'school_id': 1}]
 }}}
 That's 3 dictionaries because we now have 3 Class objects. That seems
 fine. On the other hand, why don't students appear here?

 {{{
 >>> Class.objects.values('name', 'students')
 [{'students': 1, 'name': u'Software Engineering'}, {'students': None,
 'name': u'Computer Engineering'}, {'students': 1, 'name': u'Discrete
 Mathematics'}, {'students': 2, 'name': u'Discrete Mathematics'}]
 }}}
 That's 4 dictionaries even though we only have 3 Class objects (soen,
 coen, and discrete_math). Can you imagine what would happen if the Class
 object had more M2M fields? The number of dictionaries returned would
 probably explode exponentially! Why aren't the students combined into a
 tuple or a list? Shouldn't it be 3 dictionaries like this:
 {{{
 [
 {'students': (1,), 'name': u'Software Engineering'},
 {'students': (,), 'name': u'Computer Engineering'}, # Note the empty
 tuple for students, instead of None
 {'students': (1, 2), 'name': u'Discrete Mathematics'},
 ]
 }}}

 Now, let's look at `values_list()` queries:
 {{{
 >>> Class.objects.values_list()
 [(1, 1, u'Software Engineering'), (2, 1, u'Computer Engineering'), (4, 1,
 u'Discrete Mathematics')]
 }}}
 3 tuples. Again, this seems fine except for the fact that students aren't
 included.

 {{{
 >>> Class.objects.values_list('name', 'students')
 [(u'Software Engineering', 1), (u'Computer Engineering', None),
 (u'Discrete Mathematics', 1), (u'Discrete Mathematics', 2)]
 }}}
 4 tuples even though we have 3 Class objects only! Shouldn't this be 3
 tuples like this:
 {{{
 [
 (u'Software Engineering', (1,)),
 (u'Computer Engineering', (,)), # Note the empty tuple instead of None
 (u'Discrete Mathematics', (1, 2)),
 ]
 }}}

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Re: [Django] #22268: values_list() on a ManyToManyField returns extra None's when iterated over.

[Django]

#22268: values_list() on a ManyToManyField returns extra None's when iterated 
over.
-+-
 Reporter:  k_sze|Owner:
 Type:  Bug  |  anubhav9042
Component:  Database layer   |   Status:  assigned
  (models, ORM)  |  Version:  master
 Severity:  Normal   |   Resolution:
 Keywords:  orm, values_list,| Triage Stage:  Accepted
  ManyToManyField|  Needs documentation:  0
Has patch:  0|  Patch needs improvement:  0
  Needs tests:  0|UI/UX:  0
Easy pickings:  0|
-+-

Comment (by anubhav9042):

 Replying to [comment:13 k_sze]:
 > On the one hand, I do understand that a change in behaviour would break
 backward compatibility. On the other hand, I tend to agree with
 [comment:10 comment:10] here, in that the behaviour should be modified in
 the future. To me, the correct behaviour would be to not include the
 ''extra'' `None`s.

 This is what I want to ask, if we do not want those extra `None`s, then
 what do we return in its place.
 If we just don't return anything at all, it is going to be more
 problematic.
 Consider three `Class` objects, out of which the second object doesn't
 have `student`, then if we return something like `['some_id','some_id']`
 for this, would it not be confusing for similar case when third object
 doesn't have `student`.

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Re: [Django] #22268: values_list() on a ManyToManyField returns extra None's when iterated over.

[Django]

#22268: values_list() on a ManyToManyField returns extra None's when iterated 
over.
-+-
 Reporter:  k_sze|Owner:
 Type:  Bug  |  anubhav9042
Component:  Database layer   |   Status:  assigned
  (models, ORM)  |  Version:  master
 Severity:  Normal   |   Resolution:
 Keywords:  orm, values_list,| Triage Stage:  Accepted
  ManyToManyField|  Needs documentation:  0
Has patch:  0|  Patch needs improvement:  0
  Needs tests:  0|UI/UX:  0
Easy pickings:  0|
-+-

Comment (by k_sze):

 On the one hand, I do understand that a change in behaviour would break
 backward compatibility. On the other hand, I tend to agree with
 [comment:10 comment:10] here, in that the behaviour should be modified in
 the future. To me, the correct behaviour would be to not include the
 ''extra'' `None`s. In my example, the ones from the null `year_of_birth`
 are fine and should be included. Another point of consideration that I
 would raise is whether there is any reason to believe that people are
 ''relying'' on the current behaviour (I think it would be quite strange
 for people to be ''relying on ambiguity'').

 Would it be OK to document it as a ''quirk'' that is subject to change in
 the future, and not as the ''correct bahaviour''?

 Regarding [comment:11 comment:11], I think there are possible legitimate
 uses for this kind of query. For instance, if you want a Cartesian product
 count of some M2M relation, and then run it through the Python
 collections.Counter or something.

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Re: [Django] #22268: values_list() on a ManyToManyField returns extra None's when iterated over.

[Django]

#22268: values_list() on a ManyToManyField returns extra None's when iterated 
over.
-+-
 Reporter:  k_sze|Owner:
 Type:  Bug  |  anubhav9042
Component:  Database layer   |   Status:  assigned
  (models, ORM)  |  Version:  master
 Severity:  Normal   |   Resolution:
 Keywords:  orm, values_list,| Triage Stage:  Accepted
  ManyToManyField|  Needs documentation:  0
Has patch:  0|  Patch needs improvement:  0
  Needs tests:  0|UI/UX:  0
Easy pickings:  0|
-+-
Changes (by anubhav9042):

 * status:  new => assigned
 * owner:  nobody => anubhav9042


Comment:

 I am also in favour of doc patch...as current behaviour is correct
 I will create a patch.

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Re: [Django] #22268: values_list() on a ManyToManyField returns extra None's when iterated over.

[Django]

#22268: values_list() on a ManyToManyField returns extra None's when iterated 
over.
-+-
 Reporter:  k_sze|Owner:  nobody
 Type:  Bug  |   Status:  new
Component:  Database layer   |  Version:  master
  (models, ORM)  |   Resolution:
 Severity:  Normal   | Triage Stage:  Accepted
 Keywords:  orm, values_list,|  Needs documentation:  0
  ManyToManyField|  Patch needs improvement:  0
Has patch:  0|UI/UX:  0
  Needs tests:  0|
Easy pickings:  0|
-+-

Comment (by erikr):

 Changing this to not include the None value is definitely backwards
 compatibility breaking. So far, in this ticket, we have not been able to
 reach a clear consensus on what the correct behaviour is. To me, the
 current behaviour does not seem unreasonable. The issue raised in
 comment:7 is valid, but I don't see how removing extra None's would help -
 this is simply not the right query for that question.

 Given that there is no strong case for removing the None's, I think we
 should not break backwards compatibility, and therefore keep the existing
 behaviour. If you disagree, please make sure to clarify exactly how you
 would like the behaviour to change. Otherwise, I do think a documentation
 patch would be good.

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Re: [Django] #22268: values_list() on a ManyToManyField returns extra None's when iterated over.

[Django]

#22268: values_list() on a ManyToManyField returns extra None's when iterated 
over.
-+-
 Reporter:  k_sze|Owner:  nobody
 Type:  Bug  |   Status:  new
Component:  Database layer   |  Version:  master
  (models, ORM)  |   Resolution:
 Severity:  Normal   | Triage Stage:  Accepted
 Keywords:  orm, values_list,|  Needs documentation:  0
  ManyToManyField|  Patch needs improvement:  0
Has patch:  0|UI/UX:  0
  Needs tests:  0|
Easy pickings:  0|
-+-
Changes (by pirosb3):

 * cc: pirosb3 (added)


Comment:

 I understand that it is unclear if this is an error or expected behavour,
 and that changing this will lead to backwards compatibility issues.
 I still believe this should be modified in the future. With None being a
 possible value in values_list, it makes developer's lives more difficult,
 as they need to check when iterating over the list.
 Another possible solution would be to make a documentation patch, the
 developer needs to be aware of this.

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Re: [Django] #22268: values_list() on a ManyToManyField returns extra None's when iterated over.

[Django]

#22268: values_list() on a ManyToManyField returns extra None's when iterated 
over.
-+-
 Reporter:  k_sze|Owner:  nobody
 Type:  Bug  |   Status:  new
Component:  Database layer   |  Version:  master
  (models, ORM)  |   Resolution:
 Severity:  Normal   | Triage Stage:  Accepted
 Keywords:  orm, values_list,|  Needs documentation:  0
  ManyToManyField|  Patch needs improvement:  0
Has patch:  0|UI/UX:  0
  Needs tests:  0|
Easy pickings:  0|
-+-

Comment (by anubhav9042):

 Since {{{values}}} and {{{values_list}}} return a value for all objects
 present(here {{{Class}}}).
 Therefore if a class doesn't have that field present, it will have to
 return some value, if {{{None}}} is not demanded for that field then what
 should we be wanting in place.

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Re: [Django] #22268: values_list() on a ManyToManyField returns extra None's when iterated over.

[Django]

#22268: values_list() on a ManyToManyField returns extra None's when iterated 
over.
-+-
 Reporter:  k_sze|Owner:  nobody
 Type:  Bug  |   Status:  new
Component:  Database layer   |  Version:  master
  (models, ORM)  |   Resolution:
 Severity:  Normal   | Triage Stage:  Accepted
 Keywords:  orm, values_list,|  Needs documentation:  0
  ManyToManyField|  Patch needs improvement:  0
Has patch:  0|UI/UX:  0
  Needs tests:  0|
Easy pickings:  0|
-+-

Comment (by anubhav9042):

 First thing we should make clear is that whether we want to change the
 current behaviour or not.
 Please see my previous comment: ``values`` and ``values_list`` give result
 for all objects present.

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Re: [Django] #22268: values_list() on a ManyToManyField returns extra None's when iterated over.

[Django]

#22268: values_list() on a ManyToManyField returns extra None's when iterated 
over.
-+-
 Reporter:  k_sze|Owner:  nobody
 Type:  Bug  |   Status:  new
Component:  Database layer   |  Version:  master
  (models, ORM)  |   Resolution:
 Severity:  Normal   | Triage Stage:  Accepted
 Keywords:  orm, values_list,|  Needs documentation:  0
  ManyToManyField|  Patch needs improvement:  0
Has patch:  0|UI/UX:  0
  Needs tests:  0|
Easy pickings:  0|
-+-

Comment (by k_sze):

 And I believe the problem is even more serious when the values_list is
 querying for a nullable field of a ManyToManyField. For example, if I
 modify the Student class and add a new field:

 {{{
 class Student(models.Model):
 surname = models.CharField(max_length=255)
 given_name = models.CharField(max_length=255)
 year_of_birth = models.SmallIntegerField(null=True)
 }}}

 And then I make this query:

 {{{
 >>> Class.objects.values_list('students__year_of_birth', flat=True)
 [None, None]
 }}}

 It becomes ambiguous where the `None`s come from: one of the `None`s is
 from john_smith, who has a null year_of_birth, the other `None` is because
 the other class has no student at all.

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Re: [Django] #22268: values_list() on a ManyToManyField returns extra None's when iterated over.

[Django]

#22268: values_list() on a ManyToManyField returns extra None's when iterated 
over.
-+-
 Reporter:  k_sze|Owner:  nobody
 Type:  Bug  |   Status:  new
Component:  Database layer   |  Version:  master
  (models, ORM)  |   Resolution:
 Severity:  Normal   | Triage Stage:  Accepted
 Keywords:  orm, values_list,|  Needs documentation:  0
  ManyToManyField|  Patch needs improvement:  0
Has patch:  0|UI/UX:  0
  Needs tests:  0|
Easy pickings:  0|
-+-

Comment (by pirosb3):

 I have start looking at this ticket, that is currently replicated on my
 machine.

 The query generated by the values_list statement above is:
 {{{
 (u'SELECT "m2m_and_m2o_class_students"."student_id" FROM
 "m2m_and_m2o_class" LEFT OUTER JOIN "m2m_and_m2o_class_students" ON (
 "m2m_and_m2o_class"."id" = "m2m_and_m2o_class_students"."class_id" )', ())
 }}}

 I think the issue here is related to the LEFT OUTER JOIN. We could modify
 ValuesListQuerySet.iterator and make changes to avoid this, but I am not
 sure it should be done here.
 Can anyone give me some advice? am I looking in the correct place?

 Thanks,
 Dan

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Re: [Django] #22268: values_list() on a ManyToManyField returns extra None's when iterated over.

[Django]

#22268: values_list() on a ManyToManyField returns extra None's when iterated 
over.
-+-
 Reporter:  k_sze|Owner:  nobody
 Type:  Bug  |   Status:  new
Component:  Database layer   |  Version:  master
  (models, ORM)  |   Resolution:
 Severity:  Normal   | Triage Stage:  Accepted
 Keywords:  orm, values_list,|  Needs documentation:  0
  ManyToManyField|  Patch needs improvement:  0
Has patch:  0|UI/UX:  0
  Needs tests:  0|
Easy pickings:  0|
-+-
Changes (by anubhav9042):

 * cc: anubhav9042@… (added)


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Re: [Django] #22268: values_list() on a ManyToManyField returns extra None's when iterated over.

[Django]

#22268: values_list() on a ManyToManyField returns extra None's when iterated 
over.
-+-
 Reporter:  k_sze|Owner:  nobody
 Type:  Bug  |   Status:  new
Component:  Database layer   |  Version:  master
  (models, ORM)  |   Resolution:
 Severity:  Normal   | Triage Stage:  Accepted
 Keywords:  orm, values_list,|  Needs documentation:  0
  ManyToManyField|  Patch needs improvement:  0
Has patch:  0|UI/UX:  0
  Needs tests:  0|
Easy pickings:  0|
-+-

Comment (by timo):

 I agree it's unclear what change in behavior is desired here.

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Re: [Django] #22268: values_list() on a ManyToManyField returns extra None's when iterated over.

[Django]

#22268: values_list() on a ManyToManyField returns extra None's when iterated 
over.
-+-
 Reporter:  k_sze|Owner:  nobody
 Type:  Bug  |   Status:  new
Component:  Database layer   |  Version:  master
  (models, ORM)  |   Resolution:
 Severity:  Normal   | Triage Stage:  Accepted
 Keywords:  orm, values_list,|  Needs documentation:  0
  ManyToManyField|  Patch needs improvement:  0
Has patch:  0|UI/UX:  0
  Needs tests:  0|
Easy pickings:  0|
-+-

Comment (by anubhav9042):

 One thing I want to clear out is that I think that {{{values}}} and
 {{{values_list}}} return dictionary/tuple type data for all objects
 present, hence this might not be a bug.
 eg.
 {{{
 Class.objects.values_list()
 }}}
 will give you something like
 {{{
 [(1L, 1L, u'Software Engineering'), (2L, 1L, u'Computer Engineering')]
 }}}
 thus for
 {{{
 Class.objects.values_list('students')
 }}}
 you are bound to get
 {{{
 [(1L,), (None,)]
 }}}

 Thoughts??

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Ticket URL: 
Django 
The Web framework for perfectionists with deadlines.

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Re: [Django] #22268: values_list() on a ManyToManyField returns extra None's when iterated over.

[Django]

#22268: values_list() on a ManyToManyField returns extra None's when iterated 
over.
-+-
 Reporter:  k_sze|Owner:  nobody
 Type:  Bug  |   Status:  new
Component:  Database layer   |  Version:  master
  (models, ORM)  |   Resolution:
 Severity:  Normal   | Triage Stage:  Accepted
 Keywords:  orm, values_list,|  Needs documentation:  0
  ManyToManyField|  Patch needs improvement:  0
Has patch:  0|UI/UX:  0
  Needs tests:  0|
Easy pickings:  0|
-+-
Changes (by bmispelon):

 * version:  1.6 => master
 * stage:  Unreviewed => Accepted


Comment:

 Hi,

 Indeed, there seem to be something going wrong here.
 I tried it out and the bug seems present on older versions too (I tried
 all the way to 1.4).

 Thanks.

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Re: [Django] #22268: values_list() on a ManyToManyField returns extra None's when iterated over.

[Django]

#22268: values_list() on a ManyToManyField returns extra None's when iterated 
over.
-+-
 Reporter:  k_sze|Owner:  nobody
 Type:  Bug  |   Status:  new
Component:  Database layer   |  Version:  1.6
  (models, ORM)  |   Resolution:
 Severity:  Normal   | Triage Stage:
 Keywords:  orm, values_list,|  Unreviewed
  ManyToManyField|  Needs documentation:  0
Has patch:  0|  Patch needs improvement:  0
  Needs tests:  0|UI/UX:  0
Easy pickings:  0|
-+-
Changes (by k_sze):

 * needs_better_patch:   => 0
 * type:  Uncategorized => Bug
 * needs_tests:   => 0
 * needs_docs:   => 0


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