#23386: Unexpected result when incrimenting field with F expression
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Reporter: codefisher | Owner: nobody
Type: Uncategorized | Status: new
Component: Uncategorized | Version: 1.6
Severity: Normal | Keywords:
Triage Stage: Unreviewed | Has patch: 0
Easy pickings: 0 | UI/UX: 0
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I would have thought these two expresses would be exactly the same, except
the second would be more efficient.
A: some_model.some_field += 1
B: some_model.some_field = F('some_field') + 1
I hit some unexpected behaviour when, I did this
some_model.save()
# and somewhere far far away
some_model.save()
With A, the field is incremented once, as I expected. But with B, it gets
incremented twice. I would have expected the F query to effect the next
database call, and nothing more. It might be intended, but then it is not
documented.
I could write some come to demonstrate this. I only noticed it because I
was using an import script that was creating lots of objects, and I had A
and B in the model's overridden save method. They were causing vastly
different results.
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Ticket URL: <https://code.djangoproject.com/ticket/23386>
Django <https://code.djangoproject.com/>
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