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Fixes #16855 #124

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Fixes #16855 #124

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5 changes: 4 additions & 1 deletion django/db/models/sql/query.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1745,7 +1745,10 @@ def add_select_related(self, fields):
certain related models (as opposed to all models, when
self.select_related=True).
"""
field_dict = {}
if self.select_related is False:
field_dict = {}
else:
field_dict = self.select_related
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The query.select_related has numerous states: it can be False (for no select_related), it can be True (which seems to indicate that depth based select_related should be used) or it can be a dict (for user-selected restriction). I think here field_dict could end up being True here.

In the long run it would be better to split the query.select_related to two variables: one would be query.select_related = True/False, another would ne query.select_related_restriction = None or dict_of_asked_selections.

For the time being maybe
field_dict = isinstance(self.select_related, dict) and self.select_related or {}
would do? (naturally, not tested).

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So the question now is: what to do when select_related is True? Two use cases:

# will work ok
Species.objects.select_related(depth=4).select_related('genus') 

# should get all immediate relations AND the Order
Species.objects.select_related(depth=1).select_related('genus__family__order')

I seems to me we need this split on select_related and we need to handle it intelligently, ie. 'count' depth of select related field and conditionally add it or not.

for field in fields:
d = field_dict
for part in field.split(LOOKUP_SEP):
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8 changes: 7 additions & 1 deletion tests/modeltests/select_related/models.py
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Expand Up @@ -52,8 +52,14 @@ class Genus(models.Model):
def __unicode__(self):
return self.name

class AlternativeName(models.Model):
name = models.CharField(max_length=50)
def __unicode__(self):
return self.name

class Species(models.Model):
name = models.CharField(max_length=50)
genus = models.ForeignKey(Genus)
alternative_name = models.ForeignKey(AlternativeName, null=True)
def __unicode__(self):
return self.name
return self.name
21 changes: 20 additions & 1 deletion tests/modeltests/select_related/tests.py
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Original file line number Diff line number Diff line change
Expand Up @@ -2,7 +2,7 @@

from django.test import TestCase

from .models import Domain, Kingdom, Phylum, Klass, Order, Family, Genus, Species
from .models import Domain, Kingdom, Phylum, Klass, Order, Family, Genus, Species, AlternativeName


class SelectRelatedTests(TestCase):
Expand Down Expand Up @@ -160,3 +160,22 @@ def test_depth_fields_fails(self):
Species.objects.select_related,
'genus__family__order', depth=4
)

def test_select_related_chaining(self):
'''
Regression for #16855
'''
name = AlternativeName.objects.create(name='Human')
human = Species.objects.get(name='sapiens')
human.alternative_name = name
human.save()

qs = Species.objects.select_related('genus')
qs = qs.select_related('alternative_name')
with self.assertNumQueries(1):
names = []
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Aren't these names and genus lists unused - you add to them but never read from them?

BTW above in the tests.py add an empty line before the unicode method.

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I don't think additional reading is required -- test without fix is failing. I guess the lists are not needed.

genus = []
for s in qs:
genus.append(s.genus.name)
if s.alternative_name:
names.append(s.alternative_name.name)