Django2.0手册:Managing files

Using files in models¶

When you use a FileField or
ImageField, Django provides a set of APIs you can use
to deal with that file.

Consider the following model, using an ImageField to
store a photo:

from django.db import models

class Car(models.Model):
    name = models.CharField(max_length=255)
    price = models.DecimalField(max_digits=5, decimal_places=2)
    photo = models.ImageField(upload_to='cars')

Any Car instance will have a photo attribute that you can use to get at
the details of the attached photo:

>>> car = Car.objects.get(name="57 Chevy")
>>> car.photo
<ImageFieldFile: chevy.jpg>
>>> car.photo.name
'cars/chevy.jpg'
>>> car.photo.path
'/media/cars/chevy.jpg'
>>> car.photo.url
'http://media.example.com/cars/chevy.jpg'

This object — car.photo in the example — is a File object, which means
it has all the methods and attributes described below.

For example, you can change the file name by setting the file’s
name to a path relative to the file storage’s
location (MEDIA_ROOT if you are using the default
FileSystemStorage):

>>> import os
>>> from django.conf import settings
>>> initial_path = car.photo.path
>>> car.photo.name = 'cars/chevy_ii.jpg'
>>> new_path = settings.MEDIA_ROOT + car.photo.name
>>> # Move the file on the filesystem
>>> os.rename(initial_path, new_path)
>>> car.save()
>>> car.photo.path
'/media/cars/chevy_ii.jpg'
>>> car.photo.path == new_path
True

The File object¶

Internally, Django uses a django.core.files.File instance any time it
needs to represent a file.

Most of the time you’ll simply use a File that Django’s given you (i.e. a
file attached to a model as above, or perhaps an uploaded file).

If you need to construct a File yourself, the easiest way is to create one
using a Python built-in file object:

>>> from django.core.files import File

# Create a Python file object using open()
>>> f = open('/path/to/hello.world', 'w')
>>> myfile = File(f)

Now you can use any of the documented attributes and methods
of the File class.

Be aware that files created in this way are not automatically closed.
The following approach may be used to close files automatically:

>>> from django.core.files import File

# Create a Python file object using open() and the with statement
>>> with open('/path/to/hello.world', 'w') as f:
...     myfile = File(f)
...     myfile.write('Hello World')
...
>>> myfile.closed
True
>>> f.closed
True

Closing files is especially important when accessing file fields in a loop
over a large number of objects. If files are not manually closed after
accessing them, the risk of running out of file descriptors may arise. This
may lead to the following error:

IOError: [Errno 24] Too many open files

File storage¶

Behind the scenes, Django delegates decisions about how and where to store files
to a file storage system. This is the object that actually understands things
like file systems, opening and reading files, etc.

Django’s default file storage is given by the DEFAULT_FILE_STORAGE
setting; if you don’t explicitly provide a storage system, this is the one that
will be used.

See below for details of the built-in default file storage system, and see
编写一个自定义存储系统 for information on writing your own file
storage system.

>>> from django.core.files.base import ContentFile
>>> from django.core.files.storage import default_storage

>>> path = default_storage.save('/path/to/file', ContentFile('new content'))
>>> path
'/path/to/file'

>>> default_storage.size(path)
11
>>> default_storage.open(path).read()
'new content'

>>> default_storage.delete(path)
>>> default_storage.exists(path)
False

from django.core.files.storage import FileSystemStorage
from django.db import models

fs = FileSystemStorage(location='/media/photos')

class Car(models.Model):
    ...
    photo = models.ImageField(storage=fs)