#33143: Block import-time queries
-------------------------------------+-------------------------------------
Reporter: Adam | Owner: nobody
Johnson |
Type: | Status: new
Cleanup/optimization |
Component: Database | Version: dev
layer (models, ORM) |
Severity: Normal | Keywords:
Triage Stage: | Has patch: 0
Unreviewed |
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
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It's possible to make ORM queries at import time. For example:
{{{
class Form(forms.Form):
country = forms.ChoiceField(choices=[c.name for c in
Country.objects.all()])
}}}
I see import time queries fairly frequently, and every time I have
encountered them they were a mistake. They end up querying the database
once when the web server starts and caching the data forever, which is
never desired.
Python allows imports to happen at any time, so there's no way to detect
when "import time" is over, and the app is really running. An inner import
may cause a module to be first loaded during a web request.
I therefore propose we block queries until *after* the `AppConfig.ready()`
phase. This would protect against most problems.
We could block until *before* `AppConfig.ready()`. Queries inside a
`ready()` method kind-of imply the user knows that the query is one-off at
startup. But we do encourage users to perform some imports within
`ready()` methods such as for signal registration.
--
Ticket URL: <https://code.djangoproject.com/ticket/33143>
Django <https://code.djangoproject.com/>
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