Opened 14 years ago
Closed 13 years ago
#14082 closed Bug (fixed)
modelform_factory should use the form's metaclass
Reported by: | Joseph Spiros | Owned by: | Honza Král |
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Component: | Forms | Version: | dev |
Severity: | Normal | Keywords: | ModelForm, ModelFormMetaclass, modelform_factory |
Cc: | mmitar@…, Stephen Burrows | Triage Stage: | Accepted |
Has patch: | yes | Needs documentation: | no |
Needs tests: | no | Patch needs improvement: | no |
Easy pickings: | no | UI/UX: | no |
Description
Currently, django.forms.models.modelform_factory always uses ModelFormMetaclass to create the returned form class, even in cases when the provided form class has specified its own metaclass. I've attached a patch which fixes this. Even though metaclass will always be set for ModelForm subclasses, I retained the default functionality should there have been a case where a form class without a metaclass was provided to modelform_factory.
Attachments (2)
Change History (11)
by , 14 years ago
Attachment: | modelform_factory_custom_metaclasses.diff added |
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follow-up: 2 comment:1 by , 14 years ago
Cc: | added |
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comment:2 by , 14 years ago
Replying to mitar:
I am not sure that this is the case. I play a lot with metaclasses here and it seems to work?
Metaclasses work, but only if you directly instantiate the ModelForm subclass yourself. modelform_factory dynamically creates a new form class with the passed-in class as the parent, and uses ModelFormMetaclass as the constructor. So, when using modelform_factory with ModelForm subclasses that have a custom metaclass set, that custom metaclass is ignored.
comment:3 by , 14 years ago
Owner: | changed from | to
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Status: | new → assigned |
Triage Stage: | Unreviewed → Accepted |
We still need some tests to verify the fix, but the issue is valid
comment:4 by , 14 years ago
I've made some tests for this, but it seems it really works.. Can you look at it?
https://github.com/kvbik/django/commit/c342c3089ac169fbcf285b34f65a73fd834886a7
comment:5 by , 14 years ago
Resolution: | → worksforme |
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Status: | assigned → closed |
I hope I made myself clear, that it does work for me even without the patch. But maybe you need something more specific and you can put some more tests for that.
comment:6 by , 14 years ago
Cc: | added |
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Resolution: | worksforme |
Status: | closed → reopened |
I've looked into this issue and there actually is a problem here. Essentially, the ModelFormMetaclass will be run twice.
Suppose I define the following modelform subclass:
class MyModelFormMetaclass(ModelFormMetaclass): run = 0 def __new__(*args, **kwargs): return ModelFormMetaclass.__new__(*args, **kwargs) class MyModelForm(ModelForm): __metaclass__ = MyModelFormMetaclass
If I use modelform_factory in its current state, the following calls occur:
- a call to ModelFormMetaclass.__new__
- a super() call by ModelFormMetaclass [1]
- a call to MyModelFormMetaclass.__new__ in the course of the super call. This is how type works, apparently.
- a call to ModelFormMetaclass.__new__ during MyModelFormMetaclass.__new__
This should be corrected not only because it's inelegant to be calling ModelFormMetaclass.__new__ twice and not only because it's odd that the code currently doesn't call the form's actual metaclass on principle, but also because this can cause real issues.
Just to pick an example, if I try to modify the base_fields of the form in my custom metaclass *after* calling ModelFormMetaclass myself, my changes will be overridden by ModelFormMetaclass once the stack gets back up to it.
[1] http://code.djangoproject.com/browser/django/trunk/django/forms/models.py#L194
comment:7 by , 13 years ago
Severity: | → Normal |
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Type: | → New feature |
comment:8 by , 13 years ago
Easy pickings: | unset |
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Needs tests: | unset |
Type: | New feature → Bug |
Updated the patch to r16322 - tests run with no unexpected failures. Added tests that fail iff the patch is not applied. Changed type to Bug since an erroneous behavior is being corrected.
by , 13 years ago
Attachment: | patch_r16322.diff added |
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I am not sure that this is the case. I play a lot with metaclasses here and it seems to work?