Admin does not allow removal of an image from an ImageField after it has been set, even if null=True and blank=True

As far as I know, image removal is just not yet implemented in built-in admin. There was a solution around on how to fix it in wiki on this website (checkbox "delete" appears near each image).

Duplicate of #2983.

This is not a duplicate of 2983. The issue here is setting a previously filled in ImageField? (or FileField?) to blank, not the automated deletion of files when new ones are uploaded.

Patch for admin filefield deletion

I've added an initial patch - needs a bit of cleaning up as I've made a bit of a mess wrt PEP8 so I will reupload in a moment.

In this patch I've taken the approach of False indicating a file explicitly unset, None indicating no new value. I don't particularly like that approach, but FileField is special-cased at the model, form and form field level so it defaults to preserving the current value. A cleaner approach might be to remove the special case that makes it default to preserving a value, and have FileField explicitly return the same file. But that would mean more upheaval, less compatibility.

Admin filefield deletion (updated for style)

This aproach is fine with me, but overloading False to mean "delete the file" smells bad to me. A relatively easy change that'd remove (some of) the smell would be to use a sentinel object (i.e. DeleteFile = object()) instead of False.

To offer as much compatibility as possible for anyone using ModelAdmin hooks I thought it best to preserve the ability to do

if form.cleaned_data['file']:

So I suppose that could be achieved like this

class DeleteFileType(object):
    def __nonzero__(self):
        return False

DeleteFile = DeleteFileType()

You know, maybe we're over-thinking this a bit. Why not leave cleaned_data['file'] alone, and just deal with the checkbox as a separate bit of data (cleaned_data['__delete_file'] or somesuch)? Anyone using ModelAdmin hooks will need to update 'em anyway to deal with the new features, so there's not a big change here.

Jacob: unless I'm missing something I think there's a second ticket(in the 7000s I think) that uses a MultiValueField? to pretty much do that.

#7048 for reference.