#15817: ImageField having [width|height]_field set sytematically compute the
image
dimensions in ModelForm validation process
-------------------------------------------------+-------------------------
Reporter: stan <stanislas.guerra@…> | Owner: nobody
Type: Cleanup/optimization | Status: new
Milestone: | Component: Forms
Version: 1.3 | Severity: Normal
Keywords: ImageField, dimension, | Triage Stage:
height_field, width_field, slow | Unreviewed
Has patch: 0 |
-------------------------------------------------+-------------------------
This bug is directly related to the ticket #11084 and
[http://groups.google.com/group/django-
developers/browse_thread/thread/4375ac8425002e3a this discussion on Google
Groups].
The fact is when you submit a ModelForm of an existing instance having an
ImageField with the image_height / image_width attributes set, the
validation process cause the image to be systematically opened to compute
the dimension whathever It has changed or not.
This does not happens when these attributes are not set in the field so I
guess we do not need the dimensions at this point.
This is a huge overhead in some cases as you can imagine especially with
inline_formset when you have several images related to a model ; the
simple fact of updating one single field of the parent take ages to open
every single image with the PIL.
This take place during the form validation process (.is_valid()), in the
_post_clean() method where model validation is performed.
{{{
self.instance.clean_fields(exclude=exclude) # forms.models.py (line 325 in
post_clean())
setattr(self, f.attname, f.clean(raw_value, self)) # db.models.base.py
(line 848 in clean_fields())
}}}
Which lead us to the ''ImageFileDescriptor.__set__()'' and a call to
''update_dimension_fields'' line 314 :
{{{
class ImageFileDescriptor(FileDescriptor):
"""
Just like the FileDescriptor, but for ImageFields. The only difference
is
assigning the width/height to the width_field/height_field, if
appropriate.
"""
def __set__(self, instance, value):
previous_file = instance.__dict__.get(self.field.name)
super(ImageFileDescriptor, self).__set__(instance, value)
# To prevent recalculating image dimensions when we are
instantiating
# an object from the database (bug #11084), only update dimensions
if
# the field had a value before this assignment. Since the default
# value for FileField subclasses is an instance of
field.attr_class,
# previous_file will only be None when we are called from
# Model.__init__(). The ImageField.update_dimension_fields method
# hooked up to the post_init signal handles the Model.__init__()
cases.
# Assignment happening outside of Model.__init__() will trigger
the
# update right here.
if previous_file is not None:
self.field.update_dimension_fields(instance, force=True)
}}}
At this point, I can not see a trivial and elegant patch that does not
break anything. A simple workaround (not tested) is to disable those
attributes and override the model.save() to update {height|width}_field by
myself, not so funny :-)
--
Ticket URL: <http://code.djangoproject.com/ticket/15817>
Django <http://code.djangoproject.com/>
The Web framework for perfectionists with deadlines.
--
You received this message because you are subscribed to the Google Groups
"Django updates" group.
To post to this group, send email to django-updates@googlegroups.com.
To unsubscribe from this group, send email to
django-updates+unsubscr...@googlegroups.com.
For more options, visit this group at
http://groups.google.com/group/django-updates?hl=en.
