Opened 12 years ago
Closed 11 years ago
#18361 closed Cleanup/optimization (wontfix)
Accessing a ModelChoiceField property in a template triggers QuerySet evaluation
| Reported by: | Kevin Michel | Owned by: | nobody |
|---|---|---|---|
| Component: | Forms | Version: | 1.4 |
| Severity: | Normal | Keywords: | |
| Cc: | Triage Stage: | Design decision needed | |
| Has patch: | yes | Needs documentation: | no |
| Needs tests: | no | Patch needs improvement: | no |
| Easy pickings: | no | UI/UX: | no |
Description
When reading a property of a ModelChoiceField in a template :
{{ form.something.label }}
The template languages first tries to evaluate form.something['label'].
Since ModelChoiceFields are iterable, the __getitem__ implementation
calls __iter__, which, if the field is bound to a QuerySet, force its evaluation.
A simple type check before building the list in __getitem__ can avoid this inefficiency.
Attachments (1)
Change History (3)
by , 12 years ago
| Attachment: | form_widget_iteration.diff added |
|---|
comment:1 by , 12 years ago
| Triage Stage: | Unreviewed → Design decision needed |
|---|
comment:2 by , 11 years ago
| Resolution: | → wontfix |
|---|---|
| Status: | new → closed |
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There's never going to be a way to prevent QS evaluation holistically from the template. Ultimately it's code, even if we try to limit it, so here again the answer to "it hurts when I do this" is "stop doing that."