Re: [Django] #30000: Passing QuerySet constructed with .union() causes ModelMultipleChoiceField to return wrong values

[Django]

#3: Passing QuerySet constructed with .union() causes 
ModelMultipleChoiceField
to return wrong values
-+-
 Reporter:  thoha|Owner:  nobody
 Type:  Bug  |   Status:  new
Component:  Forms|  Version:  1.11
 Severity:  Normal   |   Resolution:
 Keywords:  queryset, union, | Triage Stage:
  forms  |  Unreviewed
Has patch:  0|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-
Changes (by thoha):

 * type:  Uncategorized => Bug


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Ticket URL: 
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Re: [Django] #30000: Passing QuerySet constructed with .union() causes ModelMultipleChoiceField to return wrong values

[Django]

#3: Passing QuerySet constructed with .union() causes 
ModelMultipleChoiceField
to return wrong values
-+-
 Reporter:  thoha|Owner:  nobody
 Type:  Uncategorized|   Status:  new
Component:  Forms|  Version:  1.11
 Severity:  Normal   |   Resolution:
 Keywords:  queryset, union, | Triage Stage:
  forms  |  Unreviewed
Has patch:  0|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-

Comment (by thoha):

 After some further testing it appears the unexpected behaviour comes from
 the fact that UNION querysets cannot be filtered, which the
 ModelMultipleChoiceField apparently does out of sight. Still, I believe
 that the observed behaviour is undesired, and the field should either
 accept the union queryset and work properly, or raise an exception if a
 union queryset is passed.

 I also found that using

 {{{
 union_queryset =
 
SelectableRecords.objects.filter(other_related_thing_name__in=other_related_things)
 }}}

 instead of the for-loop results in a queryset that actually works properly
 with the ModelMultipleChoiceField. Based on
 [https://stackoverflow.com/questions/50638442/django-queryset-union-
 return-broken-queryset-filter-and-get-return-every this StackOverflow
 question].

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Re: [Django] #30000: Passing QuerySet constructed with .union() causes ModelMultipleChoiceField to return wrong values

[Django]

#3: Passing QuerySet constructed with .union() causes 
ModelMultipleChoiceField
to return wrong values
-+-
 Reporter:  thoha|Owner:  nobody
 Type:  Uncategorized|   Status:  new
Component:  Forms|  Version:  1.11
 Severity:  Normal   |   Resolution:
 Keywords:  queryset, union, | Triage Stage:
  forms  |  Unreviewed
Has patch:  0|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-
Changes (by thoha):

 * keywords:   => queryset, union, forms


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

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Re: [Django] #30000: Passing QuerySet constructed with .union() causes ModelMultipleChoiceField to return wrong values

[Django]

#3: Passing QuerySet constructed with .union() causes 
ModelMultipleChoiceField
to return wrong values
---+--
 Reporter:  thoha  |Owner:  nobody
 Type:  Uncategorized  |   Status:  new
Component:  Forms  |  Version:  1.11
 Severity:  Normal |   Resolution:
 Keywords: | Triage Stage:  Unreviewed
Has patch:  0  |  Needs documentation:  0
  Needs tests:  0  |  Patch needs improvement:  0
Easy pickings:  0  |UI/UX:  0
---+--
Description changed by thoha:

Old description:

> I have a form that displays large lists of selectable records using
> ModelMultipleChoiceFields. These fields need to show a predetermined list
> of records, obtained through some database queries performed within the
> Form's class __init__ block.
> The QuerySet required is constructed by reaching through a few ForeignKey
> relationships to retrieve the required records and then using the
> .union() method to assemble the QuerySet.
> e.g.:
>
> {{{
> # Retrieve original record:
>  base = BaseModel.objects.filter(source_name=source_name).first()
> # Get related record via ForeignKey relationship:
> related_record = base.related_record
> # related_record.other_related_things has ManyToMany relationship to
> another Model (one or more records).
> # So get them:
> other_related_things = related_record.other_related_things.all()
> # Loop through these:
> union_queryset = None
> for other_related_thing in other_related_things:
> # Each other_related_thing has a set of SelectableRecords associated
> with it, via a ForeignKey relationship from the latter model to the
> former one. This gets that QuerySet:
> other_related_thing_queryset =
> other_related_thing.selectablerecords_set.all()
> # Build union_queryset:
> if union_queryset is None:
> union_queryset = other_related_thing_queryset
> else:
> union_queryset =
> union_queryset_object.union(other_related_thing_queryset)
> # The resulting union_queryset is a unified queryset containing
> all of the required fields.
> # If only one other_related_thing exists, the result of
> evaluating the union_queryset QuerySet ought to be the
> # same as the result of evaluating
> SelectableRecords.objects.all()
> }}}
>
> However, when I pass the union_queryset to my ModelMultipleChoiceFields,
> **validating the form returns all of the records contained in
> union_queryset instead of the records selected on the form**. The form
> displays correctly.
>
> The code used for this is:
>
> {{{
> self.fields['selectable_records'] =
> forms.ModelMultipleChoiceField(queryset=union_queryset, required=False,
> label='Selectable
> records',
> widget=forms.CheckboxSelectMultiple)
> }}}
>
> Do take note that the documentation for the .union() method
> ([https://docs.djangoproject.com/en/2.1/ref/models/querysets/#union
> here]) indicates there are some limits to the QuerySet returned, and I
> assume my problem has to do with this.

New description:

 I have a form that displays large lists of selectable records using
 ModelMultipleChoiceFields. These fields need to show a predetermined list
 of records, obtained through some database queries performed within the
 Form's class __init__ block.
 The QuerySet required is constructed by reaching through a few ForeignKey
 relationships to retrieve the required records and then using the .union()
 method to assemble the QuerySet.
 e.g.:

 {{{
 # Retrieve original record:
  base = BaseModel.objects.filter(source_name=source_name).first()
 # Get related record via ForeignKey relationship:
 related_record = base.related_record
 # related_record.other_related_things has ManyToMany relationship to
 another Model (one or more records).
 # So get them:
 other_related_things = related_record.other_related_things.all()
 # Loop through these:
 union_queryset = None
 for other_related_thing in other_related_things:
 # Each other_related_thing has a set of SelectableRecords associated
 with it, via a ForeignKey relationship from the latter model to the former
 one. This gets that QuerySet:
 other_related_thing_queryset =
 other_related_thing.selectablerecords_set.all()
 # Build union_queryset:
 if union_queryset is None:
 union_queryset = other_related_thing_queryset
 else:
 union_queryset =
 union_queryset_object.union(other_related_thing_queryset)
 # The resulting union_queryset is a unified queryset containing
 all of the required fields.
 # If only one other_related_thing exists, the result of evaluating
 the union_queryset QuerySet ought to be the
 # same as the result of evaluating Selecta