InMemoryUploadedFile object has no attribute _committed

[Max Arnold]

Uploading any image to the following custom field leads to exception:

class ImageField(models.ImageField):
    __metaclass__ = models.SubfieldBase

This example is simplified as much as possible. In real project I want to store thumbnail directory path instead of full file path and use to_python/get_prep_value to do necessary transforms (according to the docs, SubfieldBase is required for to_python to work).

Traceback is below:

File "/Library/Python/2.7/site-packages/django/core/handlers/base.py" in get_response
  111.                         response = callback(request, *callback_args, **callback_kwargs)
File "/Library/Python/2.7/site-packages/django/contrib/admin/options.py" in wrapper
  307.                 return self.admin_site.admin_view(view)(*args, **kwargs)
File "/Library/Python/2.7/site-packages/django/utils/decorators.py" in _wrapped_view
  93.                     response = view_func(request, *args, **kwargs)
File "/Library/Python/2.7/site-packages/django/views/decorators/cache.py" in _wrapped_view_func
  79.         response = view_func(request, *args, **kwargs)
File "/Library/Python/2.7/site-packages/django/contrib/admin/sites.py" in inner
  197.             return view(request, *args, **kwargs)
File "/Library/Python/2.7/site-packages/django/utils/decorators.py" in _wrapper
  28.             return bound_func(*args, **kwargs)
File "/Library/Python/2.7/site-packages/django/utils/decorators.py" in _wrapped_view
  93.                     response = view_func(request, *args, **kwargs)
File "/Library/Python/2.7/site-packages/django/utils/decorators.py" in bound_func
  24.                 return func(self, *args2, **kwargs2)
File "/Library/Python/2.7/site-packages/django/db/transaction.py" in inner
  217.                 res = func(*args, **kwargs)
File "/Library/Python/2.7/site-packages/django/contrib/admin/options.py" in add_view
  882.                 self.save_model(request, new_object, form, change=False)
File "/Library/Python/2.7/site-packages/django/contrib/admin/options.py" in save_model
  665.         obj.save()
File "/Library/Python/2.7/site-packages/django/db/models/base.py" in save
  460.         self.save_base(using=using, force_insert=force_insert, force_update=force_update)
File "/Library/Python/2.7/site-packages/django/db/models/base.py" in save_base
  543.                         for f in meta.local_fields if not isinstance(f, AutoField)]
File "/Library/Python/2.7/site-packages/django/db/models/fields/files.py" in pre_save
  253.         if file and not file._committed:

Exception Type: AttributeError at /admin/db/testapp/imagetest/add/
Exception Value: 'InMemoryUploadedFile' object has no attribute '_committed'

I spent a lot of time trying to understand complex file class hierarchy (FileField, FieldFile, FileDescriptor, UploadedFile, File, storage), but now I'm stuck and not really sure if this a Django bug or error on my side. Please sorry for noise if the latter.

[Łukasz Rekucki]

AFAIK, you should only use SubfieldBase if you're subclassing Field itself. See the notes on subclassing FileField (​https://docs.djangoproject.com/en/dev/howto/custom-model-fields/#writing-a-filefield-subclass) for a better way to do what you want.