#28822: Add DBCalculatedField to model to annotate models automatically
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Reporter: Ilya | Owner: nobody
Type: New feature | Status: new
Component: Database layer | Version: master
(models, ORM) |
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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Changes (by Shai Berger):
* cc: Shai Berger (added)
* stage: Unreviewed => Accepted
Comment:
I don't really agree with the description's opening statement, that as
much logic as possible should live within models. But the feature, as
described above, has gained support and the design as described above is
mostly in consensus.
The issue with safety of local calculation is about edge cases. Examples
include different precisions and rounding rules for numeric calculations;
different timezones between web-server and database-server for date
calculations; empty string treated as null on Oracle, while `'' != None`
in Python; locale (which, on MySql for example, can be defined per column)
affecting the result of string order comparisons on the database but not
in Python, and probably more. I believe that it is very easy to be naive
about this, and this naivety may cause hard-to-debug data corruptions, so
I'd really like the naming in the API to push this point (e.g. by using a
name like `estimate` instead of `local` above).
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Ticket URL: <https://code.djangoproject.com/ticket/28822#comment:3>
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