Source code for simpleimages.utils
import os
from simpleimages.django_compat import import_by_path
def get_caller():
from django.conf import settings
caller_text = getattr(
settings,
'SIMPLEIMAGES_TRANSFORM_CALLER',
'simpleimages.callers.default'
)
return import_by_path(caller_text)
[docs]def perform_transformation(instance, field_names_to_transform=None):
'''
Transforms a model based on the fields specified in the
``transformed_fields`` attribute. This should map source image
field names to dictionaries mapping destination field name to
their transformations. For instance::
{
'image': {
'thumbnail': scale(width=10),
}
}
If ``field_names_to_transform`` is None, then it will transform
all fields. Otherwise it will only transform
from those fields specified in ``field_names_to_transform``.
:param instance: model instance to perform transformations on
:type instance: instance of :py:class:`django.db.models.Model`
:param field_names_to_transform: field names on model to perform transformations on
:type field_names_to_transform: iterable of strings or None
'''
for source_field_name, destination_dict in instance.transformed_fields.items():
if field_names_to_transform is None or source_field_name in field_names_to_transform:
for destination_field_name, transformation in destination_dict.items():
arguments = [instance, source_field_name, destination_field_name, transformation]
get_caller()(transform_field, *arguments)
[docs]def transform_field(instance, source_field_name, destination_field_name, transformation):
'''
Does an image transformation on a instance. It will get the image
from the source field attribute of the instnace, then call
the transformation function with that instance, and finally
save that transformed image into the destination field attribute
of the instance.
.. note::
If the source field is blank or the transformation returns
a false value then the destination field image will be deleted, if it
exists.
.. warning::
When the model instance is saved with the new transformed image, it uses
the ``update_fields`` argument for
:py:meth:`~django.db.models.Model.save`, to tell the model to only update
the destination field and, if set in the destination field, the
:py:attr:`~django.db.models.ImageField.height_field` and
:py:attr:`~django.db.models.ImageField.width_field`. This means that
if the saving code for the model sets any other fields, in the saving
field process, it will not save those fields to the database. This would
only happen if you introduce custom logic to the saving process of
destination field, like the dimension fields do, that updates another field
on that module. In that case, when the model is saved for the
transformation, that other field will not be saved to the database.
:param instance: model instance to perform transformations on
:type instance: instance of :py:class:`django.db.models.Model`
:param source_field_name: field name on model to find source image
:type source_field_name: string
:param destination_field_name: field name on model save transformed image to
:type destination_field_name: string
:param transformation: function, such as :py:func:`~.transforms.scale`, that takes an image files and returns a transformed image
:type transformation: function
'''
source_field = getattr(instance, source_field_name)
destination_field = getattr(instance, destination_field_name)
update_fields = [destination_field_name]
transformed_image = get_transformed_image(source_field, transformation)
if transformed_image:
destination_name = os.path.basename(source_field.name)
dimension_field_names = [
destination_field.field.height_field,
destination_field.field.width_field]
update_fields += filter(None, dimension_field_names)
destination_field.save(
destination_name,
transformed_image,
save=False
)
elif destination_field:
destination_field.delete()
else:
return
instance.save(update_fields=update_fields)
def get_transformed_image(source, transformation):
if source:
source.open()
return transformation(source)