copy_db_connection.py

#!/usr/bin/env python
# encoding=utf-8

import sys
import os
from pprint import pprint
os.environ.setdefault("DJANGO_SETTINGS_MODULE", "qa.settings")
from django.contrib.contenttypes.models import ContentType
# Output utf-8 on the command line, why is this buggy on my box?
reload(sys)
sys.setdefaultencoding("utf-8")

"""
Script to copy all data in a django project from one database connection to
another. m2m relations are not supported, unless they are explicitly defined
with through. Not very battletested.

Change settings with all caps to reflect your setup.

Inspired by http://macrotoma.blogspot.dk/2012/10/solved-move-django-from-sqlite-to-mysql.html
Replace step 6. with:

    1. Edit FROM and TO in this script
    2. run: python copy_db_connection.py collection_info
    3. Change TABLES in this script based on the output of the previous command
    4. run: python copy_db_connection.py copy_data
    5. If errors occur goto 3.
    6. Verify everything went ok
"""

# The name of the DB connection to copy from.
FROM = 'default'
# The name of the DB connection to copy to.
TO = 'slave'

# An ordered list of the tables outputted with the "collect_info" command.
# The ordering is necessary to avoid foreign key constraint errors.
TABLES = [
 (u'user', u'auth', u'user'),
 (u'group', u'auth', u'group'),
 (u'site', u'sites', u'site'),
 (u'session', u'sessions', u'session'),
 (u'content type', u'contenttypes', u'contenttype'),
 (u'log entry', u'admin', u'logentry'),
 (u'permission', u'auth', u'permission'),
 
 (u'api access', u'tastypie', u'apiaccess'),
 (u'api key', u'tastypie', u'apikey'),
 (u'migration history', u'south', u'migrationhistory'),
 
 (u'Samling af spørgsmålsamlinger', u'questions', u'questioncollectionscollection'),
 (u'Spørgsmålsamling', u'questions', u'questionscollection'),
 (u'Spørgsmål', u'questions', u'question'),
 (u'Spørgsmål til denne spørgsmålssamling', u'questions', u'questionscollectionquestion'),
 (u'Valgmulighed', u'questions', u'option'),
 
 (u'Samling af svar', u'answers', u'answerscollection'),
 (u'Svar', u'answers', u'answer'),
]


def get_model_classes():
    """
    Returns a list of model classes defined in TABLES.
    """
    models = []
    for table in TABLES:
        content_type = ContentType.objects.get(app_label=table[1], 
                                               model=table[2])
        model_class = content_type.model_class()
        assert model_class is not None, "Model class not found. Is it's app enabled in settings.py?"
        models.append(model_class)
        
    return models


def collect_info():
    """
    Outputs a list of all tables.
    """
    tables = []
    for obj in ContentType.objects.all():
        tables.append((obj.name, obj.app_label, obj.model))
        
    pprint(tables)


def copy_data():
    """
    First truncates all data, then copies data from the FROM db connection to
    the TO db connection with the tables defined in TABLES.
    """
    for model_class in get_model_classes():
        print model_class
        model_class.objects.all().using(TO).delete()
    
    # Copy data.
    for model_class in get_model_classes():
        for obj in model_class.objects.all().distinct():
            print "Saving: ", obj
            obj.save(using=TO)
            

if __name__ == "__main__":
    ERR_MSG = "Allowed commands are 'collect_info' and 'copy_data'"
    try:
        if sys.argv[1] == 'collect_info':
            collect_info()
        elif sys.argv[1] == 'copy_data':
            copy_data()
        else:
            raise Exception(ERR_MSG)
    except IndexError:
        raise Exception(ERR_MSG)
    

With a few teaks works great.
Also small typo
2. run: python copy_db_connection.py collection_info
should be
2. run: python copy_db_connection.py collect_info