#29569: AutoField.cast_db_type returns the wrong 'type' for PostgrestSQL
-------------------------------------+-------------------------------------
Reporter: Andrew | Owner: nobody
Standley |
Type: Bug | Status: new
Component: Database | Version: 2.0
layer (models, ORM) |
Severity: Normal | Keywords: cast
Triage Stage: | Has patch: 0
Unreviewed |
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
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Using PostgreSQL 10.1 I encountered a problem trying to use `Cast` with an
`AutoField`. Trying to perform a manual join on generic foreign keys:
`Item.objects.filter(pk__in=Activity.objects.filter(content_type=item_ct).annotate(casted_pk=Cast('object_pk',
AutoField())).values('casted_pk'))`
The db connection responds with a "psycopg2.ProgrammingError: type
"serial" does not exist" error.
Upon investigation, it seems that `AutoField.cast_db_type` uses the
inherited definition from `Field` and returns `AutoField.db_type`.
However `AutoField.db_type` returns 'serial', which is a "syntactical
sugar" (not a true type) in Postgresql and only valid for creation.
The issue arises when `AutoField.cast_db_type` also returns 'serial',
which is invalid.
More confusingly `AutoField.rel_db_type` has already been overridden and
correctly returns 'integer'.
I believe fixing this is as easy as copying the override of
`AutoField.rel_db_type` to `AutoField.cast_db_type`.
I'll try to at least get this implemented as a test on my fork, so that it
is easy to confirm, but in the mean time the models to reproduce are:
{{{
class Item(models.Model):
label = models.CharField(max_length=100)
cost = models.IntegerField()
class Activity(models.Model):
content_type = models.ForeignKey(ContentType,
on_delete=models.CASCADE)
object_pk = models.CharField(max_length=100)
generic_object = GenericForeignKey(fk_field='object_pk')
}}}
Reference:
PostgreSQL docs on 'serial' type
(https://www.postgresql.org/docs/10/static/datatype-numeric.html#DATATYPE-
SERIAL)
--
Ticket URL: <https://code.djangoproject.com/ticket/29569>
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