I've got a situation where one of my django apps needs to perform some
initialisation that includes processing the models from all the
installed apps -- and it needs its own models to have been initialised
also. Because of this, I can't do my initialization when the app's
__init__ module is loaded, because it may be too soon for other models
to have been loaded, and in any case, its own models have not been
loaded.
The solution I came up with was to hook the request_started signal, do
the initialisation then, and unhook the signal if initialisation
completed successfully. A corollary of this is that the
initialisation will only happen when running a server, and not (for
example) when running a shell, or tests, or otherwise using the django
framework. The code I'm using for this is below; I define an
initialise() function in my app's __init__ module and then call
prepare_app(initialise).
Is there a better way to perform application-specific initialisation,
after all apps and models have been loaded, but before other
processing begins?
Andrew.
from django.dispatch import dispatcher
from django.core.signals import request_started
class InitialisationHook(object):
"""Self-disconnecting signal hook."""
def __init__(self, init_func, dispatcher_args):
self.init_func = init_func
self.dispatcher_args = dispatcher_args
def __call__(self):
try:
self.init_func()
except:
raise
else:
# Since initialisation succeeded, don't listen for more
requests
dispatcher.disconnect(self, **self.dispatcher_args)
def prepare_app(init_func):
"""
Initialise the current app by calling ``init_func`` immediately
before
the first request. If an exception is raised by init_func, it will
be
propagated through to the handler (usually causing a 500 error),
and
initialisation will be attempted on the next request.
"""
# Connect the hook, ensuring that the dispatcher keeps a reference
to it
dispatcher_args = dict(signal=request_started, weak=False)
dispatcher.connect(InitialisationHook(init_func, dispatcher_args),
**dispatcher_args)
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