Django - how to create a file and save it to a model s FileField

Question

Here s my model   What I want to do is generate a new file and overwrite the existing one whenever a model instance is saved   class Kitten models Model       claw size           license file   models FileField blank True  upload to  license        def save self   args    kwargs            Generate a new license file overwriting any previous version          and update file path         self license file               super Request self  save  args    kwargs    I see lots of documentation about how to upload a file   But how do I generate a file  assign it to a model field and have Django store it in the right place

User · Accepted Answer

You want to have a look at FileField and FieldFile in the Django docs, and especially FieldFile.save().

Basically, a field declared as a FileField, when accessed, gives you an instance of class FieldFile, which gives you several methods to interact with the underlying file. So, what you need to do is:

self.license_file.save(new_name, new_contents)

where new_name is the filename you wish assigned and new_contents is the content of the file. Note that new_contents must be an instance of either django.core.files.File or django.core.files.base.ContentFile (see given links to manual for the details).

The two choices boil down to:

from django.core.files.base import ContentFile, File

# Using File
with open('/path/to/file') as f:
    self.license_file.save(new_name, File(f))

# Using ContentFile
self.license_file.save(new_name, ContentFile('A string with the file content'))

User · Answer

Accepted answer is certainly a good solution  but here is the way I went about generating a CSV and serving it from a view   Thought it was worth while putting this here as it took me a little bit of fiddling to get all the desirable behaviour  overwrite existing file  storing to the right spot  not creating duplicate files etc    Django 1 4 1  Python 2 7 3   Model class MonthEnd models Model       report   models FileField db index True  upload to  not used    import csv from os path import join   build and store the file def write csv        path   join settings MEDIA ROOT   files    month end    report csv       f   open path   w b         wipe the existing content     f truncate        csv writer   csv writer f      csv writer writerow   col1         for num in range 3           csv writer writerow  num          month end file   MonthEnd       month end file report name   path     month end file save    from my app models import MonthEnd   serve it up as a download def get report request       month end   MonthEnd objects get file criteria criteria       response   HttpResponse month end report  content type  text plain       response  Content-Disposition      attachment  filename report csv       return response

User · Answer

It s good practice to use a context manager or call close   in case of exceptions during the file saving process  Could happen if your storage backend is down  etc   Any overwrite behavior should be configured in your storage backend  For example S3Boto3Storage has a setting AWS S3 FILE OVERWRITE  If you re using FileSystemStorage you can write a custom mixin   You might also want to call the model s save method instead of the FileField s save method if you want any custom side-effects to happen  like last-updated timestamps  If that s the case  you can also set the name attribute of the file to the name of the file - which is relative to MEDIA ROOT  It defaults to the full path of the file which can cause problems if you don t set it - see File   init     and File name   Here s an example where self is the model instance where my file is the FileField   ImageFile  calling save   on the whole model instance instead of just FileField   import os from django core files import File  with open filepath   rb   as fi      self my file   File fi  name os path basename fi name       self save

[python] Django - how to create a file and save it to a model's FileField?

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