#22838: ModelChoiceField.cache_choices
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Reporter: mjtamlyn | Owner: nobody
Type: New feature | Status: new
Component: Forms | Version: master
Severity: Normal | Keywords:
Triage Stage: Unreviewed | Has patch: 0
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
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`ModelChoiceField` (and `MultipleModelChoiceField`) take an option
`cache_choices`. This was introduced as a backwards compatibility effort
in February 2007 (ee96c7eb2dea86e5bdaf93f7afa91b6f0128dd72) when the
fields were made to not always cache their choices (#3534).
The option is undocumented, untested and unused within Django.
There are two possible courses of action here.
Firstly, we could simply remove the option. It should have a deprecation
cycle - in particular for people with custom subclasses of
`ModelChoiceField` who pass in the option to the super.
The alternative course of action which I prefer is to harden this into an
actual feature. It already works as follows:
- Create the `ModelChoiceField` with `cache_choices=True`.
- The `ModelChoiceIterator` will cache its results on the
`ModelChoiceField` and use that cache.
What would be needed to make this a fully fledged feature in my opinion:
- An API to clear the cache (`ModelChoiceField.clear_cache()`)
- [Very possibly] Plug it in to the cache framework properly
- Tests
- Documentation
I think this would be a very useful feature, and one which I have had use
cases for often. The most obvious use cases is when working with the same
form multiple times on a page (either as part of a formset or not) the
same query is run for every form. I can call
`MyForm.fields['modelchoicefield'].clear_cache()` after all the forms are
rendered.
The biggest possible issue here is that the iterator is not used until the
form is rendered. We may need to change when the iterator is evaluated for
this case.
I may be able to provide a patch if the feature is accepted.
--
Ticket URL: <https://code.djangoproject.com/ticket/22838>
Django <https://code.djangoproject.com/>
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