#16055: Filtering over generic relations with TextField/CharField object_id
breaks
in postgres
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Reporter: anonymous | Owner: nobody
Type: Bug | Status: new
Component: contrib.contenttypes | Version: 1.3
Severity: Normal | Resolution:
Keywords: | Triage Stage: Accepted
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
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Comment (by Marc DEBUREAUX):
Manage to create something based on Simon Charette's suggestion.
Creating a custom `GenericRelation` with the following:
- `get_joining_columns` returning an empty tuple
- `get_extra_restriction` building the whole where clause with content
type **AND** primary key join with Cast
Here's the result:
{{{#!python
class CustomGenericRelation(GenericRelation):
def get_joining_columns(self, reverse_join=False):
joining_columns = super().get_joining_columns(reverse_join)
self.joining_columns = joining_columns
return tuple()
def get_extra_restriction(self, where_class, alias, remote_alias):
cond = super().get_extra_restriction(where_class, alias,
remote_alias)
from_field = self.model._meta.pk
to_field =
self.remote_field.model._meta.get_field(self.object_id_field_name)
lookup = from_field.get_lookup('exact')(
Cast(from_field.get_col(alias),
output_field=models.TextField()),
to_field.get_col(remote_alias))
cond.add(lookup, 'AND')
return cond
}}}
Giving the following:
- a model `common.History` having a `GenericForeignKey` with `object_id`
as text
- a model `generic.Twitter` having a `CustomGenericRelation` and a numeric
primary key
- and the queryset:
{{{#!python
q =
Twitter.objects.values('id').filter(id=1).annotate(count=Count('histories'))
print(q.query)
}}}
It gives the following SQL query:
{{{#!sql
SELECT
"generic_twitter"."id",
COUNT("common_history"."id") AS "count"
FROM "generic_twitter"
LEFT OUTER JOIN "common_history" ON
(((
"common_history"."content_type_id" = 29 AND
CAST("generic_twitter"."id" AS text) = "common_history"."object_id"
)))
WHERE "generic_twitter"."id" = 1
GROUP BY "generic_twitter"."id"
}}}
Instead of this one (normal behaviour):
{{{#!sql
SELECT
"generic_twitter"."id",
COUNT("common_history"."id") AS "count"
FROM "generic_twitter"
LEFT OUTER JOIN "common_history" ON
(
"generic_twitter"."id" = "common_history"."object_id" AND
("common_history"."content_type_id" = 29)
)
WHERE "generic_twitter"."id" = 1
GROUP BY "generic_twitter"."id"
}}}
--
Ticket URL: <https://code.djangoproject.com/ticket/16055#comment:14>
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