Django: Access request object from admin's form.clean()

Indeed, there is a way to solve your issue!

You will need to subclass form provided by ModelAdmin.get_form() and override it:

class BusinessDocumentCommentForm(forms.ModelForm):

    def __init__(self, *args, **kwargs):
        self.request = kwargs.pop('request', None)
        # Voila, now you can access request anywhere in your form methods by using self.request!
        super(BusinessDocumentCommentForm, self).__init__(*args, **kwargs)
        if self.request.GET.get('document_pk', False):
            #Do something
    def clean(self):
        # Do something with self.request
        # etc.    
    class Meta:
        model = BusinessDocumentComment

class BusinessDocumentCommentAdmin(admin.ModelAdmin):

    form = BusinessDocumentCommentForm     

    def get_form(self, request, obj=None, **kwargs):

        AdminForm = super(BusinessDocumentCommentAdmin, self).get_form(request, obj, **kwargs)

        class AdminFormWithRequest(AdminForm):
            def __new__(cls, *args, **kwargs):
                kwargs['request'] = request
                return AdminForm(*args, **kwargs)

        return AdminFormWithRequest