Running Custom Code on Actions in your TOM

Sometimes it would be desirable for your TOM to run custom code when certain actions happen. For example: when an observation is completed you’d like to submit your data to an outside service. Or when you add a new target you’d like to automatically search a remote catalog for matches. You could even make your TOM automatically tweet new observations! We can achieve these tasks using code hooks.

An example code hook: send an email when observation completes.

In this example, we’ll write a little bit of code to send an email when an observation record changes it’s state to ‘COMPLETED’. We’ll assume you have gone through the getting started guide, and that you have working TOM up and running called mytom.

First, let’s create a python module where the entry point to our custom code will live:

touch mytom/

Inside this module, let’s stub out a method to call when our observation changes status:

import logging

logger = logging.getLogger(__name__)

def observation_change_state(observation, previous_status):
        'Sending email, observation %s changed state from %s to %s',
        observation, previous_status, observation.status

This method, for now, will simply log the fact that we will send out an email. Note that the method takes the observation and it’s previous status as parameters.

Next, we’ll tell our TOM to execute this method when an observation changes state. This is done via the HOOKS configuration parameter in your project’s

    'target_post_save': 'tom_common.hooks.target_post_save',
    'observation_change_state': 'mytom.hooks.observation_change_state',
    'data_product_post_upload': 'tom_dataproducts.hooks.data_product_post_upload',

We changed the path for the observation_change_state method from it’s default to the module path for our custom method, mytom.hooks.observation_change_state.

Now, when an observation changes state, you should see the following in your logs:

Sending email, observation M42 @ LCO changed state from PENDING to COMPLETED

You can test this by manually changing an observation via the django admin page.

If you only wanted to know how to run code via a hook, you can stop here and implement your own code hooks. If you’d like to learn how to send an email, read on.

Sending email

Django has good support for sending emails, and you’ll need to read the documentation to get the basic setup right. Once you have the proper settings configured, sending an email in your hook becomes as simple as this:

import logging
from django.core.mail import send_mail

logger = logging.getLogger(__name__)

def observation_change_state(observation, previous_status):
    if observation.status == 'COMPLETED':
            'Sending email, observation %s changed state from %s to %s',
            observation, previous_status, observation.status
            'Observation complete',
            'The observation {} has completed'.format(observation),

That is all that is necessary for sending an email, though you might want to look into using asynchronous task runners such as dramatiq or celery.

Available code hooks

At present, there are three available code hooks.

  • target_post_save: Runs after a target is created or updated.

  • observation_change_state: Runs whenever an observation’s state is updated.

  • data_product_post_upload: Runs after a data product is successfully uploaded to the TOM.

NOTE: target_post_save does not run automatically following a programmatic create statement, such as: