This document describes Django’s file access APIs.
However, Django provides ways to write custom file storage systems that allow you to completely customize where and how Django stores files. The second half of this document describes how these storage systems work.
Consider the following model, using an ImageField to store a photo:
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 u'cars/chevy.jpg' >>> car.photo.path u'/media/cars/chevy.jpg' >>> car.photo.url u'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.
The file is saved as part of saving the model in the database, so the actual file name used on disk cannot be relied on until after the model has been saved.
Internally, Django uses a django.core.files.File instance any time it needs to represent a file. This object is a thin wrapper around Python’s built-in file object with some Django-specific additions.
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('/tmp/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('/tmp/hello.world', 'w') as f: >>> myfile = File(f) >>> for line in myfile: >>> print line >>> 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
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 编写自定义存储系统 for information on writing your own file storage system.
Though most of the time you’ll want to use a File object (which delegates to the proper storage for that file), you can use file storage systems directly. You can create an instance of some custom file storage class, or – often more useful – you can use the global default storage system:
>>> from django.core.files.storage import default_storage >>> from django.core.files.base import ContentFile >>> path = default_storage.save('/path/to/file', ContentFile('new content')) >>> path u'/path/to/file' >>> default_storage.size(path) 11 >>> default_storage.open(path).read() 'new content' >>> default_storage.delete(path) >>> default_storage.exists(path) False
See 文件存储API for the file storage API.
Django ships with a built-in FileSystemStorage class (defined in django.core.files.storage) which implements basic local filesystem file storage. Its initializer takes two arguments:
|location||Optional. Absolute path to the directory that will hold the files. If omitted, it will be set to the value of your MEDIA_ROOT setting.|
|base_url||Optional. URL that serves the files stored at this location. If omitted, it will default to the value of your MEDIA_URL setting.|
For example, the following code will store uploaded files under /media/photos regardless of what your MEDIA_ROOT setting is:
from django.db import models from django.core.files.storage import FileSystemStorage fs = FileSystemStorage(location='/media/photos') class Car(models.Model): ... photo = models.ImageField(storage=fs)