#470: Add Field.db_default for defining database defaults
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Reporter: jws | Owner: Lily
| Foote
Type: New feature | Status: assigned
Component: Database layer | Version:
(models, ORM) |
Severity: normal | Resolution:
Keywords: sql schema | Triage Stage: Accepted
Has patch: 1 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 1
Easy pickings: 0 | UI/UX: 0
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Comment (by Adrian Torres):
I would argue that there is no legitimate reason to want to set e.g. a
literal value as default through python instead of through SQL.
Query expressions seem to be supported by `Fields.default`, I haven't seen
the actual implementation but I imagine it generates SQL that calculates a
value and is set for every row in python, so it would make sense that
these are always treated as a database default as well.
Callables are not supported in the db_default implementation since it only
makes sense to process them in python, calculating and setting the value
for every row.
The only case I can think of where having both `default` and `db_default`
in a single field definition might be useful is having a default based on
a python callable and having the db_default as a fallback in case the
callable returned `None` or some "undesirable" value, but that seems
complicated and far from the common case, IMO.
For me having both `default` and `db_default` seems like an easy trap to
fall into for beginners unaware of Django's implementation details, and
for more seasoned developers a hassle and an easy mistake to make that can
be costly.
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Ticket URL: <https://code.djangoproject.com/ticket/470#comment:60>
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