#24748: GROUP BY clause incorrect with foreign key to self in MySQL
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Reporter: sparkyb | Owner: nobody
Type: Bug | Status: new
Component: Database layer (models, ORM) | Version: 1.8
Severity: Normal | Keywords: annotate mysql
Triage Stage: Unreviewed | Has patch: 0
Easy pickings: 0 | UI/UX: 0
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A query I had that previously worked in Django 1.7 is quite broken in 1.8.
When annotating a query of a model that has a a foreign key to itself, the
wrong field is grouped by. This only occurs in MySQL due a bug to the
group by primary key optimization.
Using this example model:
{{{
class Item(Model):
name = CharField(max_length=50)
parent =
ForeignKey('self',null=True,blank=True,related_name='children')
}}}
I used to be able to get a list of items with their number of children
like this:
{{{Item.objects.all().annotate(num_children=Count('children'))}}}
But in Django 1.8, this groups by parent_id instead of by id. This is
because both are selected, and the output field for both are the same, the
primary key of Item.
--
Ticket URL: <https://code.djangoproject.com/ticket/24748>
Django <https://code.djangoproject.com/>
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