Google Cloud Firestore Triggers (2nd gen)

Cloud Functions can handle events in Cloud Firestore that occur in the same Google Cloud project as the function. You can read and/or update Cloud Firestore in response to these events using the Firestore APIs and client libraries.

In a typical lifecycle, a Cloud Firestore function does the following:

  1. Waits for changes to a particular document.

  2. Triggers when an event occurs and performs its tasks.

  3. Receives a data object with a snapshot of the affected document. For write or update events, the data object contains snapshots representing document state before and after the triggering event.

Event types

Cloud Firestore supports create, update, delete, and write events. The write event encompasses all modifications to a document.

Event type Trigger
google.cloud.firestore.document.v1.created (default) Triggered when a document is written to for the first time.
google.cloud.firestore.document.v1.updated Triggered when a document already exists and has any value changed.
google.cloud.firestore.document.v1.deleted Triggered when a document with data is deleted.
google.cloud.firestore.document.v1.written Triggered when a document is created, updated or deleted.

Wildcards are written in triggers using curly braces, as follows: "projects/YOUR_PROJECT_ID/databases/(default)/documents/collection/{document_wildcard}"

Specifying the document path

To trigger your function, specify a document path to listen to. Functions only respond to document changes, and cannot monitor specific fields or collections. Below are a few examples of valid document paths:

  • users/marie: valid trigger. Monitors a single document, /users/marie.

  • users/{username}: valid trigger. Monitors all user documents. Wildcards are used to monitor all documents in the collection.

  • users/{username}/addresses: invalid trigger. Refers to the subcollection addresses, not a document.

  • users/{username}/addresses/home: valid trigger. Monitors the home address document for all users.

  • users/{username}/addresses/{addressId}: valid trigger. Monitors all address documents.

  • users/{user=**}: valid trigger. Monitors all user documents and any documents in subcollections under each user document such as /users/userID/address/home or /users/userID/phone/work.

Using wildcards and parameters

If you do not know the specific document you want to monitor, use a {wildcard} instead of the document ID:

  • users/{username} listens for changes to all user documents.

In this example, when any field on any document in users is changed, it matches a wildcard called {username}.

If a document in users has subcollections, and a field in one of those subcollections' documents is changed, the {username} wildcard is not triggered. If your goal is to respond to events in subcollections also, use the multi-segment wildcard {username=**}.

Wildcard matches are extracted from document paths. You can define as many wildcards as you like to substitute explicit collection or document IDs. You can use up to one multi-segment wildcard like {username=**}.

Event structure

This trigger invokes your function with an event similar to the one shown below: 

{
    "oldValue": { // Update and Delete operations only
        A Document object containing a pre-operation document snapshot
    },
    "updateMask": { // Update operations only
        A DocumentMask object that lists changed fields.
    },
    "value": {
        // A Document object containing a post-operation document snapshot
    }
}

Each Document object contains one or more Value objects. See the Value documentation for type references. This is especially useful if you're using a typed language (like Go) to write your functions.

Set up your Cloud Firestore database

You need a Cloud Firestore database to test the samples in this document. It must be in place before you deploy your functions. If you do not already have a Firestore database, create one as follows:

  1. Go to the Firestore Data page.

  2. Click Select Native Mode.

  3. Choose the region (location) where your database will reside. This choice is permanent.

  4. Click Create database.

The Firestore data model consists of collections that contain documents. A document contains a set of key-value pairs.

The functions you create in this tutorial are triggered when you make changes to a document inside of a specified collection.

Example 1: Hello Firestore

The sample Cloud Function below prints the fields of a triggering Cloud Firestore event:

Node.js

Use protobufjs to decode the event data. Include the google.events.cloud.firestore.v1 data.proto in your source.

functions/v2/firebase/firestore/helloFirestore/index.js 
/**
 * Cloud Event Function triggered by a change to a Firestore document.
 */
const functions = require('@google-cloud/functions-framework');
const protobuf = require('protobufjs');

functions.cloudEvent('helloFirestore', async cloudEvent => {
  console.log(`Function triggered by event on: ${cloudEvent.source}`);
  console.log(`Event type: ${cloudEvent.type}`);

  console.log('Loading protos...');
  const root = await protobuf.load('data.proto');
  const DocumentEventData = root.lookupType(
    'google.events.cloud.firestore.v1.DocumentEventData'
  );

  console.log('Decoding data...');
  const firestoreReceived = DocumentEventData.decode(cloudEvent.data);

  console.log('\nOld value:');
  console.log(JSON.stringify(firestoreReceived.oldValue, null, 2));

  console.log('\nNew value:');
  console.log(JSON.stringify(firestoreReceived.value, null, 2));
});

Python

functions/v2/firebase/hello-firestore/main.py 
from cloudevents.http import CloudEvent
import functions_framework
from google.events.cloud import firestore


@functions_framework.cloud_event
def hello_firestore(cloud_event: CloudEvent) -> None:
    """Triggers by a change to a Firestore document.

    Args:
        cloud_event: cloud event with information on the firestore event trigger
    """
    firestore_payload = firestore.DocumentEventData()
    firestore_payload._pb.ParseFromString(cloud_event.data)

    print(f"Function triggered by change to: {cloud_event['source']}")

    print("\nOld value:")
    print(firestore_payload.old_value)

    print("\nNew value:")
    print(firestore_payload.value)

Go

functions/functionsv2/firebase/hellofirestore/hellofirestore.go 

// Package hellofirestore contains a Cloud Event Function triggered by a Cloud Firestore event.
package hellofirestore

import (
	"context"
	"fmt"

	"github.com/GoogleCloudPlatform/functions-framework-go/functions"
	"github.com/cloudevents/sdk-go/v2/event"
	"github.com/googleapis/google-cloudevents-go/cloud/firestoredata"
	"google.golang.org/protobuf/proto"
)

func init() {
	functions.CloudEvent("helloFirestore", HelloFirestore)
}

// HelloFirestore is triggered by a change to a Firestore document.
func HelloFirestore(ctx context.Context, event event.Event) error {
	var data firestoredata.DocumentEventData
	if err := proto.Unmarshal(event.Data(), &data); err != nil {
		return fmt.Errorf("proto.Unmarshal: %w", err)
	}

	fmt.Printf("Function triggered by change to: %v\n", event.Source())
	fmt.Printf("Old value: %+v\n", data.GetOldValue())
	fmt.Printf("New value: %+v\n", data.GetValue())
	return nil
}

Java

functions/v2/firebase/firestore/src/main/java/functions/FirebaseFirestore.java 
import com.google.cloud.functions.CloudEventsFunction;
import com.google.events.cloud.firestore.v1.DocumentEventData;
import com.google.protobuf.InvalidProtocolBufferException;
import io.cloudevents.CloudEvent;
import java.util.logging.Logger;

public class FirebaseFirestore implements CloudEventsFunction {
  private static final Logger logger = Logger.getLogger(FirebaseFirestore.class.getName());

  @Override
  public void accept(CloudEvent event) throws InvalidProtocolBufferException {
    DocumentEventData firestorEventData = DocumentEventData.parseFrom(event.getData().toBytes());

    logger.info("Function triggered by event on: " + event.getSource());
    logger.info("Event type: " + event.getType());

    logger.info("Old value:");
    logger.info(firestorEventData.getOldValue().toString());

    logger.info("New value:");
    logger.info(firestorEventData.getValue().toString());
  }
}

C#

functions/firebase/FirebaseFirestore/Function.cs 
using CloudNative.CloudEvents;
using Google.Cloud.Functions.Framework;
using Google.Events.Protobuf.Cloud.Firestore.V1;
using Microsoft.Extensions.Logging;
using System.Collections.Generic;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;

namespace FirebaseFirestore;

public class Function : ICloudEventFunction<DocumentEventData>
{
    private readonly ILogger _logger;

    public Function(ILogger<Function> logger) =>
        _logger = logger;

    public Task HandleAsync(CloudEvent cloudEvent, DocumentEventData data, CancellationToken cancellationToken)
    {
        _logger.LogInformation("Function triggered by event on {subject}", cloudEvent.Subject);
        _logger.LogInformation("Event type: {type}", cloudEvent.Type);
        MaybeLogDocument("Old value", data.OldValue);
        MaybeLogDocument("New value", data.Value);

        // In this example, we don't need to perform any asynchronous operations, so the
        // method doesn't need to be declared async.
        return Task.CompletedTask;
    }

    /// <summary>
    /// Logs the names and values of the fields in a document in a very simplistic way.
    /// </summary>
    private void MaybeLogDocument(string message, Document document)
    {
        if (document is null)
        {
            return;
        }

        // ConvertFields converts the Firestore representation into a .NET-friendly
        // representation.
        IReadOnlyDictionary<string, object> fields = document.ConvertFields();
        var fieldNamesAndTypes = fields
            .OrderBy(pair => pair.Key)
            .Select(pair => $"{pair.Key}: {pair.Value}");
        _logger.LogInformation(message + ": {fields}", string.Join(", ", fieldNamesAndTypes));
    }
}

Deploy the Hello Firestore function

To deploy the Hello Firestore function with a Firestore trigger, run the following command in the directory that contains the sample code (or in the case of Java, the pom.xml file):

gcloud functions deploy FUNCTION_NAME \
  --gen2 \
  --runtime=RUNTIME \
  --region=REGION \
  --trigger-location=TRIGGER REGION \
  --source=. \
  --entry-point=ENTRY_POINT \
  --trigger-event-filters=type=google.cloud.firestore.document.v1.written \
  --trigger-event-filters=database='(default)' \
  --trigger-event-filters-path-pattern=document='users/{username}'

Replace the following:

  • FUNCTION_NAME: A name for your deployed function.
  • RUNTIME: The language runtime your function uses.
  • REGION: The region in which to deploy your function.
  • TRIGGER_REGION: The location of the trigger, which must be the same as the region of the Firestore database.
  • ENTRY_POINT: The entry point to your function in your source code. This is the code that will be executed when your function runs.

Use the other fields as is:

  • --trigger-event-filters=type=google.cloud.firestore.document.v1.written specifies that the function will be triggered when a document is created, updated or deleted, per the google.cloud.firestore.document.v1.written event type.
  • --trigger-event-filters=database='(default)' specifies the Firebase database. For the default database name, use (default).
  • --trigger-event-filters-path-pattern=document='users/{username}' provides the path pattern of the documents that should be monitored for relevant changes. This path pattern states that all documents in the users collection should be monitored. For more information, see Understand path patterns.

Test the Hello Firestore function

To test the "Hello Firestore" function, set up a collection called users in your Cloud Firestore database:

  1. On the Firestore Data page, click Start a collection.

  2. Specify users as the collection ID.

  3. To start adding the collection's first document, under Add its first document accept the auto-generated Document ID.

  4. Add at least one field for the document, specifying a name and value. In this example the name is "username" and the value is "rowan:"

    Screenshot that shows creating a Firestore collection

  5. When you're done, click Save.

    This action creates a new document, thereby triggering your function.

  6. To confirm that your function was triggered, click the linked name of the function in the Google Cloud console Cloud Functions Overview page to open the Function details page.

  7. Open the Logs tab and look for this string:

Function triggered by change to: //firestore.googleapis.com/projects/your-project-id/databases/(default)'

Example 2: Convert to Uppercase

The example below retrieves the value added by the user, converts the string at that location to uppercase, and replaces the value with the uppercase string:

Node.js

Use protobufjs to decode the event data. Include the google.events.cloud.firestore.v1 data.proto in your source.

functions/v2/firebase/firestore/makeUpperCase/index.js 
const functions = require('@google-cloud/functions-framework');
const Firestore = require('@google-cloud/firestore');
const protobuf = require('protobufjs');

const firestore = new Firestore({
  projectId: process.env.GOOGLE_CLOUD_PROJECT,
});

// Converts strings added to /messages/{pushId}/original to uppercase
functions.cloudEvent('makeUpperCase', async cloudEvent => {
  console.log('Loading protos...');
  const root = await protobuf.load('data.proto');
  const DocumentEventData = root.lookupType(
    'google.events.cloud.firestore.v1.DocumentEventData'
  );

  console.log('Decoding data...');
  const firestoreReceived = DocumentEventData.decode(cloudEvent.data);

  const resource = firestoreReceived.value.name;
  const affectedDoc = firestore.doc(resource.split('/documents/')[1]);

  const curValue = firestoreReceived.value.fields.original.stringValue;
  const newValue = curValue.toUpperCase();

  if (curValue === newValue) {
    // Value is already upper-case
    // Don't perform a(nother) write to avoid infinite loops
    console.log('Value is already upper-case.');
    return;
  }

  console.log(`Replacing value: ${curValue} --> ${newValue}`);
  affectedDoc.set({
    original: newValue,
  });
});

Python

functions/v2/firebase/upper-firestore/main.py 
from cloudevents.http import CloudEvent
import functions_framework
from google.cloud import firestore
from google.events.cloud import firestore as firestoredata

client = firestore.Client()


# Converts strings added to /messages/{pushId}/original to uppercase
@functions_framework.cloud_event
def make_upper_case(cloud_event: CloudEvent) -> None:
    firestore_payload = firestoredata.DocumentEventData()
    firestore_payload._pb.ParseFromString(cloud_event.data)

    path_parts = firestore_payload.value.name.split("/")
    separator_idx = path_parts.index("documents")
    collection_path = path_parts[separator_idx + 1]
    document_path = "/".join(path_parts[(separator_idx + 2) :])

    print(f"Collection path: {collection_path}")
    print(f"Document path: {document_path}")

    affected_doc = client.collection(collection_path).document(document_path)

    cur_value = firestore_payload.value.fields["original"].string_value
    new_value = cur_value.upper()

    if cur_value != new_value:
        print(f"Replacing value: {cur_value} --> {new_value}")
        affected_doc.set({"original": new_value})
    else:
        # Value is already upper-case
        # Don't perform a second write (which can trigger an infinite loop)
        print("Value is already upper-case.")

Go

functions/functionsv2/firebase/upper/upper.go 

// Package upper contains a Firestore Cloud Function.
package upper

import (
	"context"
	"errors"
	"fmt"
	"log"
	"os"
	"strings"

	"cloud.google.com/go/firestore"
	firebase "firebase.google.com/go/v4"
	"github.com/GoogleCloudPlatform/functions-framework-go/functions"
	"github.com/cloudevents/sdk-go/v2/event"
	"github.com/googleapis/google-cloudevents-go/cloud/firestoredata"
	"google.golang.org/protobuf/proto"
)

// set the GOOGLE_CLOUD_PROJECT environment variable when deploying.
var projectID = os.Getenv("GOOGLE_CLOUD_PROJECT")

// client is a Firestore client, reused between function invocations.
var client *firestore.Client

func init() {
	// Use the application default credentials.
	conf := &firebase.Config{ProjectID: projectID}

	// Use context.Background() because the app/client should persist across
	// invocations.
	ctx := context.Background()

	app, err := firebase.NewApp(ctx, conf)
	if err != nil {
		log.Fatalf("firebase.NewApp: %v", err)
	}

	client, err = app.Firestore(ctx)
	if err != nil {
		log.Fatalf("app.Firestore: %v", err)
	}

	// Register cloud event function
	functions.CloudEvent("MakeUpperCase", MakeUpperCase)
}

// MakeUpperCase is triggered by a change to a Firestore document. It updates
// the `original` value of the document to upper case.
func MakeUpperCase(ctx context.Context, e event.Event) error {
	var data firestoredata.DocumentEventData
	if err := proto.Unmarshal(e.Data(), &data); err != nil {
		return fmt.Errorf("proto.Unmarshal: %w", err)
	}

	if data.GetValue() == nil {
		return errors.New("Invalid message: 'Value' not present")
	}

	fullPath := strings.Split(data.GetValue().GetName(), "/documents/")[1]
	pathParts := strings.Split(fullPath, "/")
	collection := pathParts[0]
	doc := strings.Join(pathParts[1:], "/")

	var originalStringValue string
	if v, ok := data.GetValue().GetFields()["original"]; ok {
		originalStringValue = v.GetStringValue()
	} else {
		return errors.New("Document did not contain field \"original\"")
	}

	newValue := strings.ToUpper(originalStringValue)
	if originalStringValue == newValue {
		log.Printf("%q is already upper case: skipping", originalStringValue)
		return nil
	}
	log.Printf("Replacing value: %q -> %q", originalStringValue, newValue)

	newDocumentEntry := map[string]string{"original": newValue}
	_, err := client.Collection(collection).Doc(doc).Set(ctx, newDocumentEntry)
	if err != nil {
		return fmt.Errorf("Set: %w", err)
	}
	return nil
}

Java

functions/v2/firebase/firestore-reactive/src/main/java/functions/FirebaseFirestoreReactive.java 
import com.google.cloud.firestore.Firestore;
import com.google.cloud.firestore.FirestoreOptions;
import com.google.cloud.firestore.SetOptions;
import com.google.cloud.functions.CloudEventsFunction;
import com.google.events.cloud.firestore.v1.DocumentEventData;
import com.google.events.cloud.firestore.v1.Value;
import com.google.protobuf.InvalidProtocolBufferException;
import io.cloudevents.CloudEvent;
import java.util.Map;
import java.util.concurrent.ExecutionException;
import java.util.logging.Logger;

public class FirebaseFirestoreReactive implements CloudEventsFunction {
  private static final Logger logger = Logger.getLogger(FirebaseFirestoreReactive.class.getName());
  private final Firestore firestore;

  private static final String FIELD_KEY = "original";
  private static final String APPLICATION_PROTOBUF = "application/protobuf";

  public FirebaseFirestoreReactive() {
    this(FirestoreOptions.getDefaultInstance().getService());
  }

  public FirebaseFirestoreReactive(Firestore firestore) {
    this.firestore = firestore;
  }

  @Override
  public void accept(CloudEvent event)
      throws InvalidProtocolBufferException, InterruptedException, ExecutionException {
    if (event.getData() == null) {
      logger.warning("No data found in event!");
      return;
    }

    if (!event.getDataContentType().equals(APPLICATION_PROTOBUF)) {
      logger.warning(String.format("Found unexpected content type %s, expected %s",
          event.getDataContentType(),
          APPLICATION_PROTOBUF));
      return;
    }

    DocumentEventData firestoreEventData = DocumentEventData
        .parseFrom(event.getData().toBytes());

    // Get the fields from the post-operation document snapshot
    // https://firebase.google.com/docs/firestore/reference/rest/v1/projects.databases.documents#Document
    Map<String, Value> fields = firestoreEventData.getValue().getFieldsMap();
    if (!fields.containsKey(FIELD_KEY)) {
      logger.warning("Document does not contain original field");
      return;
    }
    String currValue = fields.get(FIELD_KEY).getStringValue();
    String newValue = currValue.toUpperCase();

    if (currValue.equals(newValue)) {
      logger.info("Value is already upper-case");
      return;
    }

    // Retrieve the document name from the resource path:
    // projects/{project_id}/databases/{database_id}/documents/{document_path}
    String affectedDoc = firestoreEventData.getValue()
        .getName()
        .split("/documents/")[1]
        .replace("\"", "");

    logger.info(String.format("Replacing values: %s --> %s", currValue, newValue));

    // Wait for the async call to complete
    this.firestore
        .document(affectedDoc)
        .set(Map.of(FIELD_KEY, newValue), SetOptions.merge())
        .get();
  }
}

C#

functions/firebase/FirestoreReactive/Function.cs 
using CloudNative.CloudEvents;
using Google.Cloud.Firestore;
using Google.Cloud.Functions.Framework;
using Google.Cloud.Functions.Hosting;
using Google.Events.Protobuf.Cloud.Firestore.V1;
using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Logging;
using System.Collections.Generic;
using System.Threading;
using System.Threading.Tasks;

namespace FirestoreReactive;

public class Startup : FunctionsStartup
{
    public override void ConfigureServices(WebHostBuilderContext context, IServiceCollection services) =>
        services.AddSingleton(FirestoreDb.Create());
}

// Register the startup class to provide the Firestore dependency.
[FunctionsStartup(typeof(Startup))]
public class Function : ICloudEventFunction<DocumentEventData>
{
    private readonly ILogger _logger;
    private readonly FirestoreDb _firestoreDb;

    public Function(ILogger<Function> logger, FirestoreDb firestoreDb) =>
        (_logger, _firestoreDb) = (logger, firestoreDb);

    public async Task HandleAsync(CloudEvent cloudEvent, DocumentEventData data, CancellationToken cancellationToken)
    {
        // Get the recently-written value. This expression will result in a null value
        // if any of the following is true:
        // - The event doesn't contain a "new" document
        // - The value doesn't contain a field called "original"
        // - The "original" field isn't a string
        string currentValue = data.Value?.ConvertFields().GetValueOrDefault("original") as string;
        if (currentValue is null)
        {
            _logger.LogWarning($"Event did not contain a suitable document");
            return;
        }

        string newValue = currentValue.ToUpperInvariant();
        if (newValue == currentValue)
        {
            _logger.LogInformation("Value is already upper-cased; no replacement necessary");
            return;
        }

        // The CloudEvent subject is "documents/x/y/...".
        // The Firestore SDK FirestoreDb.Document method expects a reference relative to
        // "documents" (so just the "x/y/..." part). This may be simplified over time.
        if (cloudEvent.Subject is null || !cloudEvent.Subject.StartsWith("documents/"))
        {
            _logger.LogWarning("CloudEvent subject is not a document reference.");
            return;
        }
        string documentPath = cloudEvent.Subject.Substring("documents/".Length);

        _logger.LogInformation("Replacing '{current}' with '{new}' in '{path}'", currentValue, newValue, documentPath);
        await _firestoreDb.Document(documentPath).UpdateAsync("original", newValue);
    }
}

Deploy the Convert to Uppercase function

The following gcloud command deploys a function that is triggered by write events on the document companies/{CompanyId}:

gcloud functions deploy FUNCTION_NAME \
  --gen2 \
  --runtime=RUNTIME \
  --trigger-location=TRIGGER REGION \
  --region=REGION \
  --source=. \
  --entry-point=ENTRY_POINT \
  --trigger-event-filters=type=google.cloud.firestore.document.v1.written \
  --trigger-event-filters=database='(default)' \
  --trigger-event-filters-path-pattern=document='messages/{pushId}'

Replace the following:

  • FUNCTION_NAME: A name for your deployed function.
  • RUNTIME: The language runtime your function uses.
  • REGION: The region in which to deploy your function.
  • TRIGGER_REGION: The location of the trigger, which must be the same as the region of the Firestore database.
  • ENTRY_POINT: The entry point to your function in your source code. This is the code that will be executed when your function runs.

Use the other fields as is:

  • --trigger-event-filters=type=google.cloud.firestore.document.v1.written specifies that the function will be triggered when a document is created, updated or deleted, per the google.cloud.firestore.document.v1.written event type.
  • --trigger-event-filters=database='(default)' specifies the Firebase database. For the default database name, use (default).
  • --trigger-event-filters-path-pattern=document='messages/{pushId}' provides the path pattern of the documents that should be monitored for relevant changes. This path pattern states that all documents in the messages collection should be monitored. For more information, see Understand path patterns.

Test the Convert to Uppercase function

To test the "Convert to Uppercase" function you just deployed, set up a collection called messages in your Cloud Firestore database:

  1. Go to the Firestore Data page.

  2. Click Start a collection.

  3. Specify messages as the collection ID.

  4. To start adding the collection's first document, under Add its first document accept the auto-generated Document ID.

  5. To trigger your deployed function, add a document where the field name is "original" and the field value is a lowercase word, for example:

    Screenshot that shows creating a Firestore collection

  6. When you save the document, you will see the lowercase word in the value field convert to uppercase.

    If you subsequently edit the field value to contain lowercase letters, that will again trigger the function, which will convert all lowercase letters to uppercase.

Limitations

Note the following limitations for Firestore triggers for Cloud Functions:

  • Ordering is not guaranteed. Rapid changes can trigger function invocations in an unexpected order.
  • Events are delivered at least once, but a single event may result in multiple function invocations. Avoid depending on exactly-once mechanics, and write idempotent functions.
  • Firestore triggers for Cloud Functions is available only for Firestore in Native mode. It is not available for Firestore in Datastore mode.