#28806: Mechanism of fetching related objects violates READ COMMITTED
assumption of
Django ORM
-------------------------------------+-------------------------------------
Reporter: Aaron Tan | Owner: nobody
Type: Bug | Status: new
Component: Database layer | Version: dev
(models, ORM) |
Severity: Normal | Resolution:
Keywords: database, read- | Triage Stage: Accepted
committed, concurrency control |
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
Comment (by Simon Charette):
I would agree that there is little Django can do here and that we should
likely close this issue as ''wontfix'' and move on. Silencing errors would
do more harm than good as previous at accessing `fk_id` could have
returned a value but then `fk` would be `None`?
We could adjust the comment but ultimately the only way to ensure the
retrieval of a graph of object that is coherent at query time is to use
`select_related` to ensure all the data is retrieved a single query. From
that time objects are not locked anyhow and the only way to ensure they
are not altered is to use `select_for_update` and friends.
I would argue that lazy fetching of related objects honours `READ
COMMITED` assumption of the ORM; if you defer relationship then fetching
at a later point in time will attempt to reconciliate your in-memory
representation of model instances with the latest committed database state
possibly resulting in exceptions.
--
Ticket URL: <https://code.djangoproject.com/ticket/28806#comment:5>
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