How to use call_command with dumpdata command to save json to file

Question

I am trying to use the call_command method to call the dumpdata command. Manually, I use it as follows to save the data to a file.

python manage.py dumpdata appname_one appname_two > /path/to/save/file.json

and it saves the json file. Now, I am in a situation where I need to call this command using the call_command method.

I am able to print out the json from the command using the following:

from django.core.management import call_command

call_command('dumpdata', 'appname_one', 'appname_two')

Is there a way I can save the given data to a file like we do it from the command line?

Answer 1

had to redirect sys.stdout to the file in order to achieve the above. Something like.

import sys

from django.core.management import call_command


sysout = sys.stdout
sys.stdout = open('filename.json', 'w')
call_command('dumpdata', 'appname_one', 'appname_two')
sys.stdout = sysout

Answer 2

An even better way is to use Django's built-in stdout redirection for their command modules. See docs here.

If you want to manipulate the stream before sending it to a file, you can also pass it a StringIO buffer:

import os
from cStringIO import StringIO

from django.core import management

def create_fixture(app_name, filename):
    buf = StringIO()
    management.call_command('dumpdata', app_name, stdout=buf)
    buf.seek(0)
    with open(filename, 'w') as f:
        f.write(buf.read())

Answer 3

I am using Django fixture magic https://github.com/davedash/django-fixture-magic and need to dump a custom fixture. I tried several ways but ended up using Amyth's answer becuase it was the only way that worked.

Here is my admin action that works with fixture magic

def export_survey(modeladmin, request, queryset):

    sysout = sys.stdout

    survey = queryset[0]
    fname = "%s.json" %(survey.slug)
    response = HttpResponse(mimetype='application/json')
    response['Content-Disposition'] = 'attachment; filename=%s' %(fname)

    sys.stdout = response
    call_command('custom_dump', 'complete_survey', survey.id)
    sys.stdout = sysout
    return response

export_survey.short_description = "Exports a single survey as a .json file"

Answer 4

DB fixtures typically compress well, and loaddata can read compressed fixtures. To write a .bz2 compressed fixture directly:

import bz2

with bz2.BZ2File('db.json.bz2', 'w', buffering=1024) as f:
  django.core.management.call_command('dumpdata', stdout=f)