Error with prewarming VersatileImageField - django

Question

I've implemented django-versatileimagefield and have gotten it to a state where I can successfully resize images in templates with the use of the following tag, for example:
As a result, I'm confident that my form.py, view.py, and template works. I have, however, recently tried to 'prewarm' the images so that when a user saves an image, a set of resized images are saved to my 'media' folder. This prevents the server from having to resize dynamically on every page load and can just grab the correctly sized image.
My problem is that when the user goes to save an image within the image upload form, they get an error.
Settings.py
VERSATILEIMAGEFIELD_SETTINGS = {
'cache_length': 2592000,
'cache_name': 'versatileimagefield_cache',
'jpeg_resize_quality': 70,
'sized_directory_name': '__sized__',
'filtered_directory_name': '__filtered__',
'placeholder_directory_name': '__placeholder__',
'create_images_on_demand': False,
'image_key_post_processor': None,
'progressive_jpeg': False
}
VERSATILEIMAGEFIELD_RENDITION_KEY_SETS = {
'image_gallery': [
('image_large', 'thumbnail__400x400'),
('image_small', 'thumbnail__900x900')
]
}
models.py
from django.db import models
from django.db.models.signals import post_save
from versatileimagefield.fields import VersatileImageField
from django.dispatch import receiver
from versatileimagefield.image_warmer import VersatileImageFieldWarmer
class ImageGallery(models.Model):
author = models.ForeignKey(User, on_delete=models.CASCADE, default=None)
image = VersatileImageField('image_gallery', upload_to=upload_location)
def __str__(self):
return self.author.username
#receiver(models.signals.post_save, sender=ImageGallery)
def warm_gallery_images(sender, instance, **kwargs):
gallery_img_warmer = VersatileImageFieldWarmer(
instance_or_queryset=instance,
rendition_key_set='image_gallery',
image_attr='image_small'
)
num_created, failed_to_create = gallery_img_warmer.warm()
Traceback
Environment:
Traceback:
File "C:\Users\jason\AppData\Local\Programs\Python\Python36\lib\site-packages\django\core\handlers\exception.py" in inner
35. response = get_response(request)
File "C:\Users\jason\AppData\Local\Programs\Python\Python36\lib\site-packages\django\core\handlers\base.py" in _get_response
128. response = self.process_exception_by_middleware(e, request)
File "C:\Users\jason\AppData\Local\Programs\Python\Python36\lib\site-packages\django\core\handlers\base.py" in _get_response
126. response = wrapped_callback(request, *callback_args, **callback_kwargs)
File "C:\Users\jason\AppData\Local\Programs\Python\Python36\lib\site-packages\django\contrib\auth\decorators.py" in _wrapped_view
21. return view_func(request, *args, **kwargs)
File "C:\Users\jason\Desktop\jason\accounts\views.py" in imagegallery
513. instance.save()
File "C:\Users\jason\AppData\Local\Programs\Python\Python36\lib\site-packages\django\db\models\base.py" in save
729. force_update=force_update, update_fields=update_fields)
File "C:\Users\jason\AppData\Local\Programs\Python\Python36\lib\site-packages\django\db\models\base.py" in save_base
769. update_fields=update_fields, raw=raw, using=using,
File "C:\Users\jason\AppData\Local\Programs\Python\Python36\lib\site-packages\django\dispatch\dispatcher.py" in send
178. for receiver in self._live_receivers(sender)
File "C:\Users\jason\AppData\Local\Programs\Python\Python36\lib\site-packages\django\dispatch\dispatcher.py" in <listcomp>
178. for receiver in self._live_receivers(sender)
File "C:\Users\jason\Desktop\jason\accounts\models.py" in warm_gallery_images
177. num_created, failed_to_create = gallery_img_warmer.warm()
File "C:\Users\jason\AppData\Local\Programs\Python\Python36\lib\site-packages\versatileimagefield\image_warmer.py" in warm
143. reduce(getattr, self.image_attr.split("."), instance)
Exception Type: AttributeError at /accounts/profile/websitesetup5/upload/
Exception Value: 'ImageGallery' object has no attribute 'image_small'
I feel like I've followed the instructions on this page, but I'm still getting this error.
http://django-versatileimagefield.readthedocs.io/en/latest/improving_performance.html#turning-off-on-demand-image-creation
I should note that I do NOT have django REST framework installed. My understanding is that it's not required for this post-save method of prewarming images.
Thanks so much!

Answer 1

It looks like the image_attr field should point to the model field image:
#receiver(models.signals.post_save, sender=ImageGallery)
def warm_gallery_images(sender, instance, **kwargs):
gallery_img_warmer = VersatileImageFieldWarmer(
instance_or_queryset=instance,
rendition_key_set='image_gallery',
image_attr='image'
)
num_created, failed_to_create = gallery_img_warmer.warm()