Django adhoc database

gistfile1.py

import string
from random import SystemRandom
from django.db import connections

key_chars = string.ascii_letters
random = SystemRandom()

class adhoc_db(object):
    """Context manager that temporarily adds a database connection.

    Exceptions are passed through, but ensures the connection and
    settings have been cleaned up from `connections.databases`.
    
    Usage:
    
        with adhoc_db(settings) as conn:
            # do something with...

    """
    def __init__(self, settings, alias=None):
        if alias is None:
            key = ''.join(random.choice(key_chars) for i in xrange(10))

        # TODO should this lock?
        assert alias not in connections.databases or \
            connections.databases[alias] == settings

        self.alias = alias
        connections.databases[alias] = settings
        self.connection = connections[alias]

    def __enter__(self):
        return self.connection

    def __exit__(self, *excinfo):
        self.connection.close()
        del connections.databases[self.alias]
        
def adhoc_db_decorator(settings, alias=None):
    def decorator(func):
        def inner(*args, **kwargs):
            with adhoc_db(settings, alias):
                return func(*args, **kwargs)
        return inner
    return decorator

Trying this out in the context of Django 1.8, and seems like the connection may not actually be dropped at the context manager exit:

In [9]: with adhoc_db(settings=connection_dictionary, alias=alias) as conn:
             # as expected, no key error here -- we have a live connection to our 'adhoc' db
   ...:     connections[alias]
   ...:     
        # exiting the context does, in fact, remove the alias from connections.databases
        # we, expectedly, KeyError here
In [12]: connections.databases[alias]
---------------------------------------------------------------------------
KeyError                                  Traceback (most recent call last)
<ipython-input-12-c2fadbc9000f> in <module>()
----> 1 connections.databases[alias]

KeyError: '/srv/gears/delete_me/temp.db'

         # I would, however, expect that accessing connections[alias] would key error as well 
         # I think right now we still have a live connections to our 'adhoc' db
In [13]: connections[alias]
Out[13]: <django.db.backends.sqlite3.base.DatabaseWrapper at 0x7fda69d21410>

I'm wondering if del connections.databases[self.alias] in line 37 should instead be

del connections[alias]

Thanks for this snippet @bruth!

I want to use this in a view and have a per view DB. How would that work?