How to write a python application that support multiple databases [closed]

Answer 1

Django supports multiple databases so all you need is some code to handle switching between them.

If you have read the docs you will see that Django allows you to supply your own custom 'router' class which decides which database to use for any given query:
https://docs.djangoproject.com/en/1.6/topics/db/multi-db/#using-routers

Since you say you want to select which db "on the front end" then presumably each user of your site could choose a different database backend. This presents a problem because the db router knows nothing about the current http request and user.

I suggest you use this 'ThreadLocal' middleware to store the current request object so you can access it from your custom router:
https://github.com/jedie/django-tools/blob/master/django_tools/middlewares/ThreadLocal.py

Let's say you save the user's chosen backend in the session as request.session['db_name'] - your router would look something like this:

from django_tools.middlewares import ThreadLocal

class RequestRouter(object):
    def db_for_read(self, model, **hints):
        request = ThreadLocal.get_current_request()
        return request.session.get('db_name', 'default')

    def db_for_write(self, model, **hints):
        request = ThreadLocal.get_current_request()
        return request.session.get('db_name', 'default')

    def allow_relation(self, obj1, obj2, **hints):
        return True

    def allow_syncdb(self, db, model):
        return True