#36074: Updating a model instance with a composite primary key through .save()
results in unnecessary re-assignment of primary key fields
-------------------------------------+-------------------------------------
Reporter: Simon | Owner: Simon Charette
Charette |
Type: Bug | Status: assigned
Component: Database | Version: dev
layer (models, ORM) |
Severity: Release | Keywords:
blocker |
Triage Stage: | Has patch: 0
Unreviewed |
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
-------------------------------------+-------------------------------------
Looking at the code that gets involved and the generated SQL It appears
that every `save` that results in an `UPDATE` for a model with a composite
primary key also includes all the primary key field in the updated fields.
For example, for a model of the form
{{{#!python
class User(models.Model):
tenant = models.ForeignKey(Tenant)
id = models.UUIDField(default=uuid.uuid4)
username = models.EmailField()
}}}
Then doing
{{{#!python
user = User.objects.create(tenant=tenant, id=1, email="[email protected]")
user.email = "[email protected]"
user.save()
# Will result in UPDATE user SET tenant_id = %s, id = %s, email = %s WHERE
tenant_id = %s AND id = %s
# ^^^^^^^^^^^^^^^^^^^^^^^ <- tenant_id and
id should not be marked for UPDATE
}}}
Will result in the following SQL
{{{#!sql
INSERT INTO user(tenant_id, id, email) VALUES (%s, %s, %s)
UPDATE user SET tenant_id = %s, id = %s, email = %s WHERE tenant_id = %s
AND id = %s
}}}
But the `UPDATE` statement should '''not''' set `tenant_id` and `id` as
they are part of the primary key lookup. The `UPDATE` should be
{{{#!sql
UPDATE user SET email = %s WHERE tenant_id = %s AND id = %s
}}}
which is due to a non-audited usage of `.primary_key` in `save_tables
{{{#!diff
diff --git a/django/db/models/base.py b/django/db/models/base.py
index a7a26b405c..6d66080c20 100644
--- a/django/db/models/base.py
+++ b/django/db/models/base.py
@@ -1091,10 +1091,11 @@ def _save_table(
for a single table.
"""
meta = cls._meta
+ pk_fields = meta.pk_fields
non_pks_non_generated = [
f
for f in meta.local_concrete_fields
- if not f.primary_key and not f.generated
+ if f not in pk_fields and not f.generated
]
if update_fields:
}}}
and makes me fear there might be others lying around that went unnoticed.
--
Ticket URL: <https://code.djangoproject.com/ticket/36074>
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