#36855: Field.pre_save() called twice during save() in Django 6.0 when inserting
new records
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Reporter: nino-robotfutures- | Type: Bug
co | Component: Database
Status: new | layer (models, ORM)
Version: 6.0 | Severity: Normal
Keywords: | Triage Stage:
| Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
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Commit 94680437 introduced a change where Field.pre_save() can be called
twice during Model.save() for new records:
Diff:
https://github.com/django/django/commit/94680437a45a71c70ca8bd2e68b72aa1e2eff337
Full method:
https://github.com/django/django/blob/94680437a45a71c70ca8bd2e68b72aa1e2eff337/django/db/models/base.py#L1085-L1164
Previously, pre_save() was only called once in the values comprehension.
Impact:
This is a breaking change for custom model fields that:
- Have side effects in pre_save() (e.g., registering
transaction.on_commit callbacks)
- Transform the value in a way that's not idempotent
- Maintain internal state based on pre_save() being called once per save
Example:
A custom field that registers an on_commit callback in pre_save() will
now register it twice, causing the callback to execute twice.
Expected behavior:
Field.pre_save() should be called exactly once per Model.save()
operation, regardless of whether the save results in an INSERT or UPDATE.
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Ticket URL: <https://code.djangoproject.com/ticket/36855>
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