Cloud Functions — Firestore Triggers

Cloud Functions is a feature provided by Firebase for running server codes at Google infrastructures in response to events triggered by Firebase events and HTTPS requests.

Cloud Functions is a feature provided by Firebase for running server codes at Google infrastructures in response to events triggered by Firebase events and HTTPS requests. Developer does not have to handle the maintenance and scalability issues. Firebase automatically scales up computing resources to match the usage patterns of your users. Each function runs in isolation in its own environment with its own configuration.Developer just has to write the business logic and let Google handle the server for us.

There are a lots of available Firebase events and one of them is Firestore event. Firestore notifies Cloud Functions once any document is created, updated and deleted within the specific collection. It is useful for adding extra information at document initialisation, validating information when document is updated and notifying admins / users once their information is deleted.

The implementation is not difficult but with some tricks. Lets see here!

1. onCreate

const functions = require("firebase-functions")
    /*
    Example of new data: {
     'fooKey': 'fooValue'
    }
    */
    exports.onCreateTrigger = functions.firestore
        .document('fooCollection/{docId}')
        .onCreate((queryDocumentSnapshot, eventContext) => {
            // ID of newly created document
            const newlyCreatedDocumentID = eventContext.params.docId

            // Retrieve value from data
            const createdData = queryDocumentSnapshot.data();
            const fooValueSyntax1 = createdDate.fooKey;
            const fooValueSyntax2 = createdDate["fooKey"];
            const fooValueSyntax3 = queryDocumentSnapshot.get("fooKey");

            return 0
        });
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OnCreateTrigger.js hosted with ❤ by GitHub

onCreate is triggered once a new document in a specific collection ( fooCollection at line 8) is created. The callback contains a QueryDocumentSnapshot and an EventContext. Document id and document data can be retrieved from them for further checking (See line 11 to line 17).

google firebase-cloud-functions firestore firebase gcp function

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