pythondjangoformsimagemodeling
Django - Save multiple versions of an Image
My application needs to save multiple versions of an uploaded Image. One high quality image and another one just for thumbnails use (low quality). Currently this is working most of the time but sometimes the save method simply fails and all of my Thumbnail images are getting deleted, especially then if I use the remove_cover checkbox at my form
raise ValueError("The '%s' attribute has no file associated with it." % self.field.name) app | ValueError: The 'postcover_tn' attribute has no file associated with it.
-> See full trace here: https://pastebin.com/hgieMGet
models.py
class Post(models.Model):
id = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
author = models.ForeignKey(User, on_delete=models.CASCADE)
title = models.CharField()
content = models.TextField(blank=False)
postcover = models.ImageField(
verbose_name="Post Cover",
blank=True,
null=True,
upload_to=image_uploads,
)
postcover_tn = models.ImageField(
verbose_name="Post Cover Thumbnail",
blank=True,
null=True,
upload_to=image_uploads,
)
published_date = models.DateTimeField(auto_now_add=True, null=True)
def save(self, *args, **kwargs):
super(Post, self).save(*args, **kwargs)
if self.postcover:
if not (self.postcover_tn and os.path.exists(self.postcover_tn.path)):
image = Image.open(self.postcover)
outputIoStream = BytesIO()
baseheight = 500
hpercent = baseheight / image.size[1]
wsize = int(image.size[0] * hpercent)
imageTemproaryResized = image.resize((wsize, baseheight))
imageTemproaryResized.save(outputIoStream, format='PNG')
outputIoStream.seek(0)
self.postcover = InMemoryUploadedFile(outputIoStream, 'ImageField',
"%s.png" % self.postcover.name.split('.')[0], 'image/png',
sys.getsizeof(outputIoStream), None)
image = Image.open(self.postcover)
outputIoStream = BytesIO()
baseheight = 175
hpercent = baseheight / image.size[1]
wsize = int(image.size[0] * hpercent)
imageTemproaryResized = image.resize((wsize, baseheight))
imageTemproaryResized.save(outputIoStream, format='PNG')
outputIoStream.seek(0)
self.postcover_tn = InMemoryUploadedFile(outputIoStream, 'ImageField',
"%s.png" % self.postcover.name.split('.')[0], 'image/png',
sys.getsizeof(outputIoStream), None)
elif self.postcover_tn:
self.postcover_tn.delete()
super(Post, self).save(*args, **kwargs)
It also seems that I'm not able to properly resolve:
- self.postcover_tn.delete() -> Unresolved attribute reference 'delete' for class 'InMemoryUploadedFile'
- self.postcover_tn.path -> Unresolved attribute reference 'path' for class 'InMemoryUploadedFile'
forms.py:
def save(self, commit=True):
instance = super(PostForm, self).save(commit=False)
if self.cleaned_data.get('remove_cover'):
try:
os.unlink(instance.postcover.path)
except OSError:
pass
instance.postcover = None
if commit:
instance.save()
return instance
Solution
maybe if we look at the problem from another angle, we could solve it otherwise, out of the box. signals are very handy when it comes to handle images (add, update and delete) and below how i managed to solve your issue:
in models.py:
# from django.template.defaultfilters import slugify
class Post(models.Model):
id = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
author = models.ForeignKey(User, on_delete=models.CASCADE)
title = models.CharField()
# slug = models.SlugField('slug', max_length=255,
# unique=True, null=True, blank=True,
# help_text='If blank, the slug will be generated automatically from the given title.'
# )
content = models.TextField(blank=False)
# ------------------------------------------------------------------------------------
# rename images with the current post id/pk (which is UUID) and keep the extension
# for cover thumbnail we append "_thumbnail" to the name
# e.g:
# img/posts/77b122a3d241461b80c51adc41d719fb.jpg
# img/posts/77b122a3d241461b80c51adc41d719fb_thumbnail.jpg
def upload_cover(instance, filename):
ext = filename.split('.')[-1]
filename = '{}.{}'.format(instance.id, ext)
path = 'img/posts/'
return '{}{}'.format(path, filename)
postcover = models.ImageField('Post Cover',
upload_to=upload_cover, # callback function
null=True, blank=True,
help_text=_('Upload Post Cover.')
)
def upload_thumbnail(instance, filename):
ext = filename.split('.')[-1]
filename = '{}_thumbnail.{}'.format(instance.id, ext)
path = 'img/posts/'
return '{}{}'.format(path, filename)
postcover_tn = models.ImageField('Post Cover Thumbnail',
upload_to=upload_thumbnail, # callback function
null=True, blank=True,
help_text=_('Upload Post Cover Thumbnail.')
)
# ------------------------------------------------------------------------------------
published_date = models.DateTimeField(auto_now_add=True, null=True)
def save(self, *args, **kwargs):
# i moved the logic to signals
# if not self.slug:
# self.slug = slugify(self.title)
super(Post, self).save(*args, **kwargs)
create new file and rename it signals.py (near to models.py):
import io
import sys
from PIL import Image
from django.core.files.uploadedfile import InMemoryUploadedFile
from django.dispatch import receiver
from django.db.models.signals import pre_save, pre_delete
from .models import Post
# DRY
def image_resized(image, h):
name = image.name
_image = Image.open(image)
content_type = Image.MIME[_image.format]
r = h / _image.size[1] # ratio
w = int(_image.size[0] * r)
imageTemproaryResized = _image.resize((w, h))
file = io.BytesIO()
imageTemproaryResized.save(file, _image.format)
file.seek(0)
size = sys.getsizeof(file)
return file, name, content_type, size
@receiver(pre_save, sender=Post, dispatch_uid='post.save_image')
def save_image(sender, instance, **kwargs):
# add image (cover | thumbnail)
if instance._state.adding:
# postcover
file, name, content_type, size = image_resized(instance.postcover, 500)
instance.postcover = InMemoryUploadedFile(file, 'ImageField', name, content_type, size, None)
# postcover_tn
file, name, content_type, size = image_resized(instance.postcover_tn, 175)
instance.postcover_tn = InMemoryUploadedFile(file, 'ImageField', name, content_type, size, None)
# update image (cover | thumbnail)
if not instance._state.adding:
# we have 2 cases:
# - replace old with new
# - delete old (when 'clear' checkbox is checked)
# postcover
old = sender.objects.get(pk=instance.pk).postcover
new = instance.postcover
if (old and not new) or (old and new and old.url != new.url):
old.delete(save=False)
# postcover_tn
old = sender.objects.get(pk=instance.pk).postcover_tn
new = instance.postcover_tn
if (old and not new) or (old and new and old.url != new.url):
old.delete(save=False)
@receiver(pre_delete, sender=Post, dispatch_uid='post.delete_image')
def delete_image(sender, instance, **kwargs):
s = sender.objects.get(pk=instance.pk)
if (not s.postcover or s.postcover is not None) and (not s.postcover_tn or s.postcover_tn is not None):
s.postcover.delete(False)
s.postcover_tn.delete(False)
in apps.py:
we need to register signals in apps.py since we use decorators @receiver:
from django.apps import AppConfig
from django.utils.translation import ugettext_lazy as _
class BlogConfig(AppConfig): # change to the name of your app
name = 'blog' # and here
verbose_name = _('Blog Entries')
def ready(self):
from . import signals
and this is the first screen shot of post admin area
since the thumbnail is generated from post cover, as UI/UX good practices there's no need to show a second input file for post cover thumbnail (i kept the second image field read only in admin.py).
below is the second screenshot after i uploaded the image
PS: the screenshot is taken from another app that i'm working on, so there's little changes, in your case you should see
- Post Cover instead Featured Image
Currently: img/posts/8b0be417db564c53ad06cb493029e2ca.jpg(seeupload_cover()inmodels.py) insteadCurrently: img/blog/posts/featured/8b0be417db564c53ad06cb493029e2ca.jpg
in admin.py
# "img/posts/default.jpg" and "img/posts/default_thumbnail.jpg" are placeholders
# grab to 2 image placeholders from internet and put them under "/static" folder
def get_post_cover(obj):
src = obj.postcover.url if obj.postcover and \
hasattr(obj.postcover, 'url') else os.path.join(
settings.STATIC_URL, 'img/posts/default.jpg')
return mark_safe('<img src="{}" height="500" style="border:1px solid #ccc">'.format(src))
get_post_cover.short_description = ''
get_post_cover.allow_tags = True
def get_post_cover_thumbnail(obj):
src = obj.postcover_tn.url if obj.postcover_tn and \
hasattr(obj.postcover_tn, 'url') else os.path.join(
settings.STATIC_URL, 'img/posts/default_thumbnail.jpg')
return mark_safe('<img src="{}" height="175" style="border:1px solid #ccc">'.format(src))
get_post_cover_thumbnail.short_description = ''
get_post_cover_thumbnail.allow_tags = True
class PostAdmin(admin.ModelAdmin):
list_display = ('title', .. )
fields = (
'author', 'title', 'content',
get_post_cover, get_post_cover_thumbnail, 'postcover',
)
readonly_fields = (get_post_cover, get_post_cover_thumbnail)
[..]
and finally you don't need any delete logic in save() function in forms.py