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PostGreSQL LISTEN/NOTIFY functionality, via psycopg2.

Project description

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This package makes it simple to use PostGreSQL’s NOTIFY/LISTEN eventing system from Python in a consistent, pleasing manner.

Note that this project officially supports Python 3.6+. This is primarily due to static typing.

Example

The following shows an example of the package in action.

Assumptions

  • PostGreSQL server is running locally.
  • default database (postgres) is available.
  • table exists in database in the public schema with the name orders.
from psycopg2 import connect
from psycopg2_pgevents.trigger import install_trigger, \
    install_trigger_function, uninstall_trigger, uninstall_trigger_function
from psycopg2_pgevents.event import poll, register_event_channel, \
    unregister_event_channel

connection = connect(dsn='postgres:///postgres')
connection.autocommit = True

install_trigger_function(connection)
install_trigger(connection, 'orders')
register_event_channel(connection)

try:
    print('Listening for events...')
    while True:
        for evt in poll(connection):
            print('New Event: {}'.format(evt))
except KeyboardInterrupt:
    print('User exit via Ctrl-C; Shutting down...')
    unregister_event_channel(connection)
    uninstall_trigger(connection, 'orders')
    uninstall_trigger_function(connection)
    print('Shutdown complete.')

Troubleshooting

  • The connection’s autocommit property must be enabled for this package to operate correctly. This requirement is provided by PostGreSQL’s NOTIFY/LISTEN mechanism.
  • The same connection that is used with register_event_channel() must be used with poll() in order to receive events. This is due to the nature of how PostGreSQL manages “listening” connections.
  • If the table that you’d like to listen to is not in the public schema, the schema name must be given as a keyword argument in the install_trigger() method.

Authorship and License

Written by Shawn Wallis and distributed under the MIT license.

Project details


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