Suffering "Stale" Choices for FilePathField - django

Question

I have a FilePathField in a form that displays directory contents as
expected. However if I add or remove a file to/from the directory the
change is not updated in the form.
Here is the from:
from django import forms
class MyForm(forms.Form):
the_file = forms.FilePathField(path='c:/temp')
and the corresponding view:
from django.shortcuts import render_to_response, get_object_or_404
from forms import MyForm
def test(request):
form = MyForm()
return render_to_response('test.html', {'form' : form})

Answer 1

I ran into this today, after noticing that new folders weren't being reflected in the select menu.
The FilePathField is initialized once, when django starts up (when the Form class is parsed by python). The contents of the directory are then stored in the field itself, and then persist for the lifetime of the program.
This behavior is unexpected (at least by me) and not explicitly documented.
The discussion below implies that this only happens when a FilePathField is used in an explicit Form class, rather than in a dynamically generated ModelForm.
See: https://groups.google.com/forum/#!searchin/django-developers/FilePathField$20refresh/django-developers/mHK-9N75swM/3k13dC5HVQoJ
And the relevant bug: https://code.djangoproject.com/ticket/16429
Neither has received much attention on the forums, so I suspect this falls into edge-case territory, probably because the fixes for it are likely to be messy.
Update I've implemented a silly workaround. Whenever you need a new form, the __init__ method is called. In that method, initialize a new FilePathField with the same arguments are the original one. The new one will have a fresh copy of the directory entries in it, and replace the stale choices with the fresh copy.
To keep from abusing the file system, keep a copy of these choices around in the cache for 5 seconds.
from django import forms
from django.core.cache import cache
class MyAwesomeForm(forms.Form):
_filepath_kw = dict(path='/some/dir',
label="Path to source images.",
recursive=True, allow_files=False,
allow_folders=True)
my_field = forms.FilePathField(**_filepath_kw)
def __init__(self, **kwargs):
key = 'filepath-cache-key'
choices = cache.get(key)
if not choices:
field = forms.FilePathField(**self._filepath_kw)
choices = field.choices
cache.set(key, choices, 5)
super().__init__(**kwargs)
self.base_fields['source'].choices = choices
If your directory is huge, storing zillions of file records in the cache is likely quite slow and probably a bad idea.
This will cause validation issues if the file system changes right after the POST, but, that's probably a good thing.
I'm pushing this change to an application this afternoon, so if I find terrible unforeseen consequences I'll update this answer.

Answer 2

If you dont want to use a cache but you were happy with that each time you call this form it reads the actual files or folders, then you could use this solution:
class ApproveUpdateForm(forms.Form):
#to ensure that the file list is updated each time ApproveUpdateForm is called
def __init__(self, **kwargs):
super().__init__(**kwargs)
self.fields['app'] = forms.FilePathField(path=settings.EXAMPLE_EXCH_DIR, match='.*\.tar.gz',
label=_("Application"))
self.fields['app'].widget.attrs['class'] = 'form-control'