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 · 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

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

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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