Showing posts with label paste. Show all posts
Showing posts with label paste. Show all posts

Monday, September 7, 2009

Running SQLAlchemy scripts off of pylon's paste configurations

I've come across a situation where I want to be able to use cron to launch scripts that automate some tasks (fetch info from 3rd party, scramble their data into my database format, write to my database). I want to be able to use the models I've already created in SQLAlchemy, along with the configuration of SQLAlchemy in my paste configuration files (development.ini, production.ini) in these scripts.

I don't need all of the bells and whistles of pylons, just the SQLAlchemy stuff. Luckily, there are some convenience functions that seem to have been made to deal with a situation just like this one. Here's the code:


import sys
from paste.deploy import appconfig
from sqlalchemy import engine_from_config
from myapp.model import init_model

def setup_environment():
if len(sys.argv) != 2:
print 'Usage: Need to specify config file.'
sys.exit(1)

config_filename = sys.argv[1]
config = appconfig('config:%s' % config_filename, relative_to='.')
engine = engine_from_config(config)
init_model(engine)


Of course, replace "myapp" with the name of your application.

Getting the configuration filename from the command-line arguments could of course be put somewhere else, so I'll just skip talking about that. The two main functions are appconfig and engine_from_config.

appconfig is from paste.deploy, which reads the configuration file and returns a dictionary-like object. engine_from_config is from SQLAlchemy and takes a dictionary-like object, retrieves SQLAlchemy-specific configurations, and uses the configurations to create an engine object.