id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
21413	"select_related ""row, fields misalignment"" in SQLCompiler.fill_related_selections()"	anonymous	nobody	"Given this models for example:


{{{
class Place(models.Model):
    name = models.CharField(max_length=50)
    address = models.CharField(max_length=80)

class Restaurant(Place):
    serves_hot_dogs = models.BooleanField()
    serves_pizza = models.BooleanField()
}}}

When using select related to prefetch the child, the child fields are not initialized properly:


{{{
>>> Restaurant.objects.create(name='Bobs Cafe', address=""Somewhere"", serves_pizza=True, serves_hot_dogs=True)
<Restaurant: Restaurant object>

>>> p = Place.objects.all().select_related('restaurant')[0]

>>> vars(p.restaurant)
{'_place_ptr_cache': <Place: Place object>,
 '_state': <django.db.models.base.ModelState at 0x2e791d0>,
 'address': u'Somewhere',
 'id': 1L,
 'name': u'Bobs Cafe',
 'place_ptr_id': 1L,
 'serves_hot_dogs': 1,
 'serves_pizza': 1}
}}}

''serves_pizza'' and ''serves_hot_dogs'' are set to ''1'' instead of ''True''!
The cause of this bug is kind of tricky. It is actually a general defect because of a ""row, fields misalignment"" in SQLCompiler.fill_related_selections(). 
[https://github.com/django/django/blob/master/django/db/models/sql/compiler.py#L650]:
''self.query.related_select_cols'' returns:
{{{
[SelectInfo(col=(u't13781_restaurant', u'place_ptr_id'), field=<django.db.models.fields.AutoField: id>), 
SelectInfo(col=(u't13781_restaurant', 'serves_hot_dogs'), field=<django.db.models.fields.CharField: name>), 
SelectInfo(col=(u't13781_restaurant', 'serves_pizza'), field=<django.db.models.fields.CharField: address>)]
}}}

But it only turns up when using SQL backends that use the misaligned fields for converting the row values depending on the field type (mainly when ''resolve_columns()'' is implemented). So for example in MySQL this only happens when boolean fields on the child model are involved, because in this special case the field information is interpreted.
[https://github.com/django/django/blob/master/django/db/backends/mysql/compiler.py#L10]:
{{{
if (field and field.get_internal_type() in (""BooleanField"", ""NullBooleanField"") and
  value in (0, 1)):
  value = bool(value)
}}}

It won't appear using SQLite but i guess it will appear using Oracle (only tested SQLite and MySQL).

It might be somehow related to  [https://code.djangoproject.com/ticket/21203 #21203] and [https://code.djangoproject.com/ticket/21126 #21126]. 


"	Bug	new	Database layer (models, ORM)	dev	Normal		select_related parent inheritance subclass		Unreviewed	0	0	0	0	0	0