Python vs. Node.js Event Payloads in Firebase Cloud Functions

Question

I am in the process of writing a Cloud Function for Firebase via the Python option. I am interested in Firebase Realtime Database Triggers; in other words I am willing to listen to events that happen in my Realtime Database.

The Python environment provides the following signature for handling Realtime Database triggers:

def handleEvent(data, context):
    # Triggered by a change to a Firebase RTDB reference.
    # Args:
         # data (dict): The event payload.
         # context (google.cloud.functions.Context): Metadata for the event.

This is looking good. The data parameter provides 2 dictionaries; 'data' for notifying the data before the change and 'delta' for the changed bits.

The confusion kicks in when comparing this signature with the Node.js environment. Here is a similar signature from theNode.js world:

exports.handleEvent = functions.database.ref('/path/{objectId}/').onWrite((change, context) => {}

In this signature, the change parameter is pretty powerful and it seems to be of type firebase.database.DataSnapshot. It has nice helper methods such as hasChild() or numChildren() that provide information about the changed object.

The question is: Does Python environment have a similar DataSnapshot object? With Python, do I have to query the database to get the number of children for example? It really isn't clear what Python environment can and can't do.

Related API/Reference/Documentation:

• Firebase Realtime DB Triggers: https://cloud.google.com/functions/docs/calling/realtime-database

• DataSnapshot Reference: https://firebase.google.com/docs/reference/js/firebase.database.DataSnapshot

Answer 1

The python runtime currently doesn't have a similar object structure. The firebase-functions SDK is actually doing a lot of work for you in creating objects that are easy to consume. Nothing similar is happening in the python environment. You are essentially getting a pretty raw view at the payload of data contained by the event that triggered your function.

If you write Realtime Database triggers for node, not using the Firebase SDK, it will be a similar situation. You'll get a really basic object with properties similar to the python dictionary.

This is the reason why use of firebase-functions along with the Firebase SDK is the preferred environment for writing triggers from Firebase products. The developer experience is superior: it does a bunch of convenient work for you. The downside is that you have to pay for the cost of the Firebase Admin SDK to load and initialize on cold start.

Note that might be possible for you to parse the event and create your own convenience objects using the Firebase Admin SDK for python.