#29072: only()/defer() vs select_related()
-------------------------------------+-------------------------------------
Reporter: Дилян | Owner: nobody
Палаузов |
Type: New | Status: new
feature |
Component: Database | Version: master
layer (models, ORM) |
Severity: Normal | Keywords:
Triage Stage: | Has patch: 0
Unreviewed |
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
-------------------------------------+-------------------------------------
Provided
{{{
class M(models.Model):
n = models.IntegerField()
r = models.IntegerField()
t = models.IntegerField()
s = models.IntegerField()
u = models.IntegerField()
class F(models.Model):
g = models.ForeignKey(M, on_delete=models.CASCADE)
a = models.IntegerField()
b = models.IntegerField()
c = models.IntegerField()
d = models.IntegerField()
e = models.IntegerField()
}}}
I want to obtain with a queryset all fields from F and M.n, but not the
other fields of M like M.r. This works
{{{F.objects.select_related('g').defer('g__r', 'g__t', 'g__s', 'g__u')}}}
but I don't like it, as I want to say only M.n has to be obtained, and not
the others. prefetch_related is also suboptimal, as it creates two SQL
queries instead of one. {{{only()}}} does not let me specify 'All fields
of F'.
{{{F.objects.select_related('g__n')}}} would fit from logic, but does not
work ({{{django.core.exceptions.FieldError: Non-relational field given in
select_related: 'n'. Choices are: (none)}}})
Please make {{{select_related()}}} accept the above expression.
This applies to both master and 1.11.
--
Ticket URL: <https://code.djangoproject.com/ticket/29072>
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