Best effort to regenerate the thumbnail when the associated image is updated

In a django Model, I keep an ImageField "image" and an associated "thumbnail", based on from imagekit.models.ImageSpecField.

I might need to rebuild the image, keeping the same filename for the bitmap.

Obviously, the thumbnail needs to be updated as well; my first attempt was:

self.thumbnail.generate(force=True)

but that's not enough; despite the force=True parameter, the thumbnail remains unchanged.

After some trials and errors, I ended up with the following workaround:

class MyModel(model.Model):

    ...

    image = models.ImageField(_('Image'), null=True, blank=True, upload_to=get_acquisition_media_file_path)
    thumbnail = ImageSpecField(source='image', processors=[ResizeToFill(200, 100)], format='PNG')

    ...

    def save_image_from_data(self):

        # Create a new random image
        from random import randint
        rgb = (randint(0, 255), randint(0, 255), randint(0, 255))
        image_size = (200, 200)
        image = PILImage.new('RGB', image_size, rgb)
        with io.BytesIO() as output:
            image.save(output, format="PNG")
            contents = output.getvalue()

        # Best effort to remove the thumbnail, if any
        try:
            file = self.thumbnail.file
        #except FileNotFoundError:
        except:
            pass
        try:
            cache_backend = self.thumbnail.cachefile_backend
            cache_backend.cache.delete(cache_backend.get_key(file))
            #self.thumbnail.storage.delete(file)
            self.thumbnail.storage.delete(file.name)
        except:
            pass

        # Save image
        self.image = ContentFile(contents, "acquisition_%d.png" % self.position)
        self.save()

        # Regenerate thumbnail
        self.thumbnail.generate(force=True)

        return True

Thumbnails cleanup

ImageKit has a bug where files are cached and not deleted right away:

https://github.com/matthewwithanm/django-imagekit/issues/229#issuecomment-315690575

An interesting solution to the is the following.

UNTESTED: I didn't try this yet in a real situation

from django.db.models.signals import post_delete

    @staticmethod
    def post_delete(sender, instance, **kwargs):
        for field in ['thumbnail', ]:
            field = getattr(instance, field)
            try:
                file = field.file
            except FileNotFoundError:
                pass
            else:
                cache_backend = field.cachefile_backend
                cache_backend.cache.delete(cache_backend.get_key(file))
                field.storage.delete(file)
        instance.file.delete(save=False)

post_delete.connect(MyModel.post_delete, sender=MyModel)

References

• How to cleanup cache backend and remove generated thumbnails from storage #229

from imagekit.utils import get_cache
get_cache().clear()