django set image delete old reference and prevent delete default

despite of many mordern website employ an OSS for serving image, I still want to build a backend to manage small thumbnails locally.

however, django image field is a bit tricky.

there are three views I may change image reference:

• models.py
• views.py
• forms.py

I used to do it simply by:

forms.py

request.user.profile.image = self.files['image']

and I always have a default

models.py

class Profile(models.Model):
    user = models.OneToOneField(User, on_delete=models.CASCADE)
    image = ProcessedImageField(
        default='profile/default.jpg', 
        upload_to='profile', 
        processors=[ResizeToFill(*THUMBNAIL_SIZE)],
        format='JPEG',
        options={'quality': THUMBNAIL_QUALITY}, 
    )

After a lot of testing, I found that it always result in an issue, can be among:

• default image file get deleted.

• if the image has been set before, it holds an value that is not the default, when I reset it, the old referenced file is not deleted and will occupy disk storage.

to do it perfectly, I decided to write a global function for import, whenever I want to set an image, call it

from django.conf import settings

def setImage(instance, attr, file):
    """ instance will be saved """
    if file:
        ifield = getattr(instance, attr)
        # old reference, can be default
        iurl = ifield.url
        # default
        durl = settings.MEDIA_URL + instance._meta.get_field(attr).get_default()
        if iurl != durl:
            # old reference is not default
            # delete old reference and free up space
            ifield.delete(save=True)
        # set new file 
        setattr(ifield, attr, file)
    instance.save()

pretty straight-forward. however, in testing, I found the image will never be set. Following are the possibale reasons I have eliminated:

• form multipart enctype attribute
• ajax processData, contentType is correctly set
• save in model class is not overriden

if it’s all ok, where went wrong? I logged out all the values.

setImage(self.user.profile, 'image', self.files['image'])
# self.files['image'] has valid value and is passed 
# to setImage, which I think, is not garbage collected

def setImage(instance, attr, file):
    """ instance will be saved """
    print('======')
    print(file)
    if file:
        ifield = getattr(instance, attr)
        iurl = ifield.url
        durl = settings.MEDIA_URL + instance._meta.get_field(attr).get_default()
        print(iurl)
        print(durl)
        if iurl != durl:
            ifield.delete(save=True)
            print(f'--- del {iurl}')
        setattr(ifield, attr, file)
        print('----res')
        print(getattr(ifield, attr))
        print(ifield.image)
    print('--- ins')
    print(instance)
    instance.save()
    print('--- after save')
    print(instance.image.url)
    print(getattr(instance, attr))

the field has a default value, and I upload the screen shot in testing.

======
Screen Shot 2022-11-03 at 10.59.41 pm.png
/media/profile/default.jpg
/media/profile/default.jpg
----res
Screen Shot 2022-11-03 at 10.59.41 pm.png
Screen Shot 2022-11-03 at 10.59.41 pm.png
--- ins
tracey
--- after save
/media/profile/default.jpg
profile/default.jpg

---

why the image is not setting, anybody have any ideas?

---

after tons of testing, only a line went wrong and just simple a wrong variable.

def setImage(instance, attr, file):
    """ instance will be saved """
    if file:
        ifield = getattr(instance, attr)
        iurl = ifield.url
        durl = settings.MEDIA_URL + instance._meta.get_field(attr).get_default()
        if iurl != durl:
            ifield.delete(save=True)
        setattr(instance, attr, file)
        instance.save()