Extend Cloud Run with event triggers using Cloud Run functions

With Cloud Run functions, you can deploy code to handle events triggered by changes in your Cloud Run database. This lets you add server-side functionality without running your own servers.

This guide describes how to create triggers for Cloud Run functions from Firestore events.

You can trigger your Cloud Run functions from events in a Firestore database. When triggered, your function reads and updates a Firestore database in response to these events through the Firestore APIs and client libraries .

The process of Firestore events triggering a Cloud Run function consists of the following steps:

The service waits for changes to a particular document.
When a change occurs, the service is triggered and performs its tasks.
The service 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.

Before you begin

Make sure you have set up a new project for Cloud Run as described in the setup page.
Enable the Artifact Registry, Cloud Build, Cloud Run Admin API, Eventarc, Firestore Cloud Logging, and Pub/Sub APIs:

Enable the APIs

Required roles

You or your administrator must grant the deployer account and the trigger identity. Optionally, grant the Pub/Sub service agent the following IAM roles.

Required roles for the deployer account

To get the permissions that you need to trigger from Firestore events, ask your administrator to grant you the following IAM roles on your project:

Cloud Build Editor ( roles/cloudbuild.builds.editor )
Cloud Run Admin ( roles/run.admin )
Datastore Owner ( roles/datastore.owner )
Eventarc Admin ( roles/eventarc.admin )
Logs View Accessor ( roles/logging.viewAccessor )
Project IAM Admin ( roles/resourcemanager.projectIamAdmin )
Service Account Admin ( roles/iam.serviceAccountAdmin )
Service Account User ( roles/iam.serviceAccountUser )
Service Usage Admin ( roles/serviceusage.serviceUsageAdmin )

For more information about granting roles, see Manage access to projects, folders, and organizations .

You might also be able to get the required permissions through custom roles or other predefined roles .

Note that by default, Cloud Build permissions include permissions to upload and download Artifact Registry artifacts .

Required roles for the trigger identity

Make note of the Compute Engine default service account as you will you attach it to an Eventarc trigger to represent the identity of the trigger for testing purposes. This service account is automatically created after enabling or using a Google Cloud service that uses Compute Engine, and with the following email format:
```
 PROJECT_NUMBER 
-compute@developer.gserviceaccount.com
```
Replace PROJECT_NUMBER with your Google Cloud project number. You can find your project number on the Welcome page of the Google Cloud console or by running the following command:
```
gcloud  
projects  
describe  
 PROJECT_ID 
  
--format = 
 'value(projectNumber)' 
```
For production environments, we strongly recommend creating a new service account and granting it one or more IAM roles that contain the minimum permissions required and follow the principle of least privilege .

Note:
The iam.automaticIamGrantsForDefaultServiceAccounts organization policy constraint prevents the Editor role from being automatically granted to default service accounts. If you created your organization after May 3, 2024, this constraint is enforced by default.

We strongly recommend that you enforce this constraint to disable the automatic role grant. If you disable the automatic role grant, you must decide which roles to grant to the default service accounts, and then grant these roles yourself.

If the default service account already has the Editor role, we recommend that you replace the Editor role with less permissive roles.To safely modify the service account's roles, use Policy Simulator to see the impact of the change, and then grant and revoke the appropriate roles .
By default, Cloud Run services are only callable by Project Owners, Project Editors, and Cloud Run Admins and Invokers. You can control access on a per-service basis ; however, for testing purposes, grant the Cloud Run Invoker role ( run.invoker ) on the Google Cloud project to the Compute Engine service account. This grants the role on all Cloud Run services and jobs in a project.
```
gcloud  
projects  
add-iam-policy-binding  
 PROJECT_ID 
  
 \ 
  
--member = 
serviceAccount: PROJECT_NUMBER 
-compute@developer.gserviceaccount.com  
 \ 
  
--role = 
roles/run.invoker
```
Note that if you create a trigger for an authenticated Cloud Run service without granting the Cloud Run Invoker role, the trigger is created successfully and is active. However, the trigger will not work as expected and a message similar to the following appears in the logs:
The request was not authenticated. Either allow unauthenticated invocations or set the proper Authorization header.

Grant the Eventarc Event Receiver role ( roles/eventarc.eventReceiver ) on the project to the Compute Engine default service account so that the Eventarc trigger can receive events from event providers.

gcloud  
projects  
add-iam-policy-binding  
 PROJECT_ID 
  
 \ 
  
--member = 
serviceAccount: PROJECT_NUMBER 
-compute@developer.gserviceaccount.com  
 \ 
  
--role = 
roles/eventarc.eventReceiver

Optional role for the Pub/Sub service agent

If you enabled the Cloud Pub/Sub service agent on or before April 8, 2021, to support authenticated Pub/Sub push requests, grant the Service Account Token Creator role ( roles/iam.serviceAccountTokenCreator ) to the service agent. Otherwise, this role is granted by default:
```
gcloud  
projects  
add-iam-policy-binding  
 PROJECT_ID 
  
 \ 
  
--member = 
serviceAccount:service- PROJECT_NUMBER 
@gcp-sa-pubsub.iam.gserviceaccount.com  
 \ 
  
--role = 
roles/iam.serviceAccountTokenCreator
```

Set up your Firestore database

Before you deploy your service, you must create a Firestore database:

Go to the Firestore page .
Select Create a Firestore database.
In the Name your databasefield, enter a Database ID , such as firestore-db .
In the Configuration optionssection, Firestore nativeis selected by default along with the applicable security rules.
In Location type, select Regionand choose the region for where your database is to reside. This choice is permanent.
Click Create database.

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

Write a Firestore-triggered function

To write a function that responds to Firestore events, prepare to specify the following during deployment:

a trigger event type
a trigger event filter to select the documents associated with the function
the function code to run

Event types

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.
`google.cloud.firestore.document.v1.created.withAuthContext`	Same as `created` but adds authentication information.
`google.cloud.firestore.document.v1.updated.withAuthContext`	Same as `updated` but adds authentication information.
`google.cloud.firestore.document.v1.deleted.withAuthContext`	Same as `deleted` but adds authentication information.
`google.cloud.firestore.document.v1.written.withAuthContext`	Same as `written` but adds authentication information.

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

Trigger event filters

To trigger your service, specify a document path to listen to. The document path must be in the same Google Cloud project as the service.

Here are a few examples of valid document paths:

users/marie : Monitors a single document, /users/marie .
users/{username} : Monitors all user documents. Wildcards are used to monitor all documents in the collection.
users/{username}/addresses/home : Monitors the home address document for all users.
users/{username}/addresses/{addressId} : Monitors all address documents.
users/{user=**} : Monitors all user documents and any documents in subcollections under each user document such as /users/userID/address/home or /users/userID/phone/work .
users/{username}/addresses : invalid address path. Refers to the subcollection addresses , not a document.

Wildcards and parameters

If you don't 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=**} .

Function code

See examples for how to use Firestore in Native Mode events to trigger a Cloud Run function.

Include the proto dependencies in your source

You must include the Cloud Run data.proto file in the source directory for your function. This file imports the following protos which you must also include in your source directory:

Use the same directory structure for the dependencies. For example, place struct.proto within google/protobuf .

These files are required to decode event data. If your function source does not include these files, it returns an error when it runs.

Event attributes

Each event includes data attributes that include information about the event such as the time the event triggered. Cloud Run adds additional data about the database and document involved in the event. You can access these attributes as follows:

Java

 logger 
 . 
 info 
 ( 
 "Function triggered by event on: " 
  
 + 
  
 event 
 . 
 getSource 
 ()); 
 logger 
 . 
 info 
 ( 
 "Event type: " 
  
 + 
  
 event 
 . 
 getType 
 ()); 
 logger 
 . 
 info 
 ( 
 "Event time " 
  
 + 
  
 event 
 . 
 getTime 
 ()); 
 logger 
 . 
 info 
 ( 
 "Event project: " 
  
 + 
  
 event 
 . 
 getExtension 
 ( 
 "project" 
 )); 
 logger 
 . 
 info 
 ( 
 "Event location: " 
  
 + 
  
 event 
 . 
 getExtension 
 ( 
 "location" 
 )); 
 logger 
 . 
 info 
 ( 
 "Database name: " 
  
 + 
  
 event 
 . 
 getExtension 
 ( 
 "database" 
 )); 
 logger 
 . 
 info 
 ( 
 "Database document: " 
  
 + 
  
 event 
 . 
 getExtension 
 ( 
 "document" 
 )); 
 // For withAuthContext events 
 logger 
 . 
 info 
 ( 
 "Auth information: " 
  
 + 
  
 event 
 . 
 getExtension 
 ( 
 "authid" 
 )); 
 logger 
 . 
 info 
 ( 
 "Auth information: " 
  
 + 
  
 event 
 . 
 getExtension 
 ( 
 "authtype" 
 ));

Node.js

 console 
 . 
 log 
 ( 
 `Function triggered by event on: 
 ${ 
 cloudEvent 
 . 
 source 
 } 
 ` 
 ); 
 console 
 . 
 log 
 ( 
 `Event type: 
 ${ 
 cloudEvent 
 . 
 type 
 } 
 ` 
 ); 
 console 
 . 
 log 
 ( 
 `Event time: 
 ${ 
 cloudEvent 
 . 
 time 
 } 
 ` 
 ); 
 console 
 . 
 log 
 ( 
 `Event project: 
 ${ 
 cloudEvent 
 . 
 project 
 } 
 ` 
 ); 
 console 
 . 
 log 
 ( 
 `Event location: 
 ${ 
 cloudEvent 
 . 
 location 
 } 
 ` 
 ); 
 console 
 . 
 log 
 ( 
 `Database name: 
 ${ 
 cloudEvent 
 . 
 database 
 } 
 ` 
 ); 
 console 
 . 
 log 
 ( 
 `Document name: 
 ${ 
 cloudEvent 
 . 
 document 
 } 
 ` 
 ); 
 // For withAuthContext events 
 console 
 . 
 log 
 ( 
 `Auth information: 
 ${ 
 cloudEvent 
 . 
 authid 
 } 
 ` 
 ); 
 console 
 . 
 log 
 ( 
 `Auth information: 
 ${ 
 cloudEvent 
 . 
 authtype 
 } 
 ` 
 );

Python

 print 
 ( 
 f 
 "Function triggered by change to: 
 { 
 cloud_event 
 [ 
 'source' 
 ] 
 } 
 " 
 ) 
 print 
 ( 
 f 
 "Event type: 
 { 
 cloud_event 
 [ 
 'type' 
 ] 
 } 
 " 
 ) 
 print 
 ( 
 f 
 "Event time: 
 { 
 cloud_event 
 [ 
 'time' 
 ] 
 } 
 " 
 ) 
 print 
 ( 
 f 
 "Event project: 
 { 
 cloud_event 
 [ 
 'project' 
 ] 
 } 
 " 
 ) 
 print 
 ( 
 f 
 "Location: 
 { 
 cloud_event 
 [ 
 'location' 
 ] 
 } 
 " 
 ) 
 print 
 ( 
 f 
 "Database name: 
 { 
 cloud_event 
 [ 
 'database' 
 ] 
 } 
 " 
 ) 
 print 
 ( 
 f 
 "Document: 
 { 
 cloud_event 
 [ 
 'document' 
 ] 
 } 
 " 
 ) 
 // 
 For 
 withAuthContext 
 events 
 print 
 ( 
 f 
 "Auth information: 
 { 
 cloud_event 
 [ 
 'authid' 
 ] 
 } 
 " 
 ) 
 print 
 ( 
 f 
 "Auth information: 
 { 
 cloud_event 
 [ 
 'authtype' 
 ] 
 } 
 " 
 )

Event structures

This trigger invokes your service with an event similar to:

 { 
  
 "oldValue" 
 : 
  
 { 
  
 // Update and Delete operations only 
  
 A 
  
  Docume 
 nt 
 
  
 objec 
 t 
  
 co 
 nta 
 i 
 n 
 i 
 n 
 g 
  
 a 
  
 pre 
 - 
 opera 
 t 
 io 
 n 
  
 docume 
 nt 
  
 s 
 na 
 psho 
 t 
  
 }, 
  
 "updateMask" 
 : 
  
 { 
  
 // Update operations only 
  
 A 
  
  Docume 
 nt 
 Mask 
 
  
 objec 
 t 
  
 t 
 ha 
 t 
  
 lis 
 ts 
  
 cha 
 n 
 ged 
  
 f 
 ields. 
  
 }, 
  
 "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.

Create triggers for functions

Click the tab for instructions using the tool of your choice.

Console

When you use the Google Cloud console to create a function, you can also add a trigger to your function. Follow these steps to create a trigger for your function:

In the Google Cloud console, go to Cloud Run:

Go to Cloud Run
Click Write a function, and enter the function details. For more information about configuring functions during deployment, see Deploy functions .
In the Triggersection, click Add trigger.
Select Firestore trigger .
In the Eventarc triggerpane, modify the trigger details as follows:
1. Enter a name for the trigger in the Trigger namefield, or use the default name.
2. Select a Trigger typefrom the list:
  - Google Sourcesto specify triggers for Pub/Sub, Cloud Storage, Firestore, and other Google event providers.
  - Third-partyto integrate with non-Google providers that offer an Eventarc source. For more information, see Third-party events in Eventarc .
3. Select Firestore from the Event providerlist, to select a product that provides the type of event for triggering your function. For the list of event providers, see Event providers and destinations .
4. Select type=google.cloud.firestore.document.v1.created from the Event typelist. Your trigger configuration varies depending on the supported event type. For more information, see Event types .
5. In the Filters section, select a database, operation and attribute values, or use the default selections.
6. If the Regionfield is enabled, select a location for the Eventarc trigger. In general, the location of an Eventarc trigger should match the location of the Google Cloud resource that you want to monitor for events. In most scenarios, you should also deploy your function in the same region. See Understand Eventarc locations for more details about Eventarc trigger locations.
7. In the Service accountfield, select a service account. Eventarc triggers are linked to service accounts to use as an identity when invoking your function. Your Eventarc trigger's service account must have the permission to invoke your function. By default, Cloud Run uses the Compute Engine default service account .
8. Optionally, specify the Service URL pathto send the incoming request to. This is the relative path on the destination service to which the events for the trigger should be sent. For example: / , /route , route , and route/subroute .
Once you've completed the required fields, click Save trigger.

gcloud

When you create a function using the gcloud CLI, you must first deploy your function, and then create a trigger. Follow these steps to create a trigger for your function:

Run the following command in the directory that contains the sample code to deploy your function:
```
 gcloud run deploy FUNCTION 
\
        --source . \
        --function FUNCTION_ENTRYPOINT 
\
        --base-image BASE_IMAGE_ID 
\
        --region REGION 
 
```
Replace:
- FUNCTION with the name of the function you are deploying. You can omit this parameter entirely, but you will be prompted for the name if you omit it.
- FUNCTION_ENTRYPOINT with the entry point to your function in your source code. This is the code Cloud Run executes when your function runs. The value of this flag must be a function name or fully-qualified class name that exists in your source code.
- BASE_IMAGE_ID with the base image environment for your function. For more details about base images and the packages included in each image, see Runtimes base images .
- REGION with the Google Cloud region where you want to deploy your function. For example, europe-west1 .
Run the following command to create a trigger that filters events:
```
 gcloud eventarc triggers create TRIGGER_NAME 
\
    --location= EVENTARC_TRIGGER_LOCATION 
\
    --destination-run-service= FUNCTION 
\
    --destination-run-region= REGION 
\
    --event-filters="type=google.cloud.firestore.document.v1.created" \
    --service-account= PROJECT_NUMBER 
-compute@developer.gserviceaccount.com 
```
Replace:
- TRIGGER_NAME with the name for your trigger.
- EVENTARC_TRIGGER_LOCATION with the location for the Eventarc trigger. In general, the location of an Eventarc trigger should match the location of the Google Cloud resource that you want to monitor for events. In most scenarios, you should also deploy your function in the same region. For more information, see Eventarc locations .
- FUNCTION with the name of the function you are deploying.
- REGION with the Cloud Run region of the function.
- PROJECT_NUMBER with your Google Cloud project number. Eventarc triggers are linked to service accounts to use as an identity when invoking your function. Your Eventarc trigger's service account must have the permission to invoke your function. By default, Cloud Run uses the Default compute service account.
Each event-filters flag specifies a type of event, with the function triggering only when an event meets all of the criteria specified in its event-filters flags. Each trigger must have an event-filters flag specifying a supported event type , such as a new document written to Firestore or a file uploaded to Cloud Storage. You can't change the event filter type after creation. To change the event filter type, you must create a new trigger and delete the old one. Optionally, you can repeat the --event-filters flag with a supported filter in the form ATTRIBUTE=VALUE to add more filters.

Terraform

To create an Eventarc trigger for a Cloud Run function, see Create a trigger using Terraform .

Examples

The following examples describe how to use Firestore in Native Mode events to trigger a Cloud Run function.

Example 1: Hello Firestore function

The following sample prints the fields of a triggering Firestore event:

Node.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

  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 
 ( 
 " 
 \n 
 Old value:" 
 ) 
 print 
 ( 
 firestore_payload 
 . 
 old_value 
 ) 
 print 
 ( 
 " 
 \n 
 New value:" 
 ) 
 print 
 ( 
 firestore_payload 
 . 
 value 
 )

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 you omit `DiscardUnknown`, protojson.Unmarshal returns an error 
  
 // when encountering a new or unknown field. 
  
 options 
  
 := 
  
 proto 
 . 
 UnmarshalOptions 
 { 
  
 DiscardUnknown 
 : 
  
 true 
 , 
  
 } 
  
 err 
  
 := 
  
 options 
 . 
 Unmarshal 
 ( 
 event 
 . 
 Data 
 (), 
  
& data 
 ) 
  
 if 
  
 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

  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 
 
  
 firestoreEventData 
  
 = 
  
  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 
 ( 
 firestoreEventData 
 . 
  getOldValue 
 
 (). 
 toString 
 ()); 
  
 logger 
 . 
 info 
 ( 
 "New value:" 
 ); 
  
 logger 
 . 
 info 
 ( 
 firestoreEventData 
 . 
  getValue 
 
 (). 
 toString 
 ()); 
  
 } 
 }

C#

  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 function

To deploy the Hello Firestore function, run the following command:

If you haven't already done so, set up your Firestore database .

To deploy the function, see Create triggers for functions .

Test the function

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

In the Google Cloud console, go to the Firestore databases page:

Go to Firestore
Click Start a collection.
Specify users as the collection ID.
To start adding the collection's first document, under Add its first documentaccept the auto-generated Document ID.
Add at least one field for the document, specifying a name and value. For example, in Field name, enter username , and in Field value, enter rowan .
When you're done, click Save.

This action creates a new document, thereby triggering your function.
To confirm that your function was triggered, click the linked name of the function in the Google Cloud console Cloud Run Overview page to open the Service detailspage.
Select the Logstab and look for this string:

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

Example 2: Convert to Uppercase function

The following example 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.

  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

  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

  // 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 you omit `DiscardUnknown`, protojson.Unmarshal returns an error 
  
 // when encountering a new or unknown field. 
  
 options 
  
 := 
  
 proto 
 . 
 UnmarshalOptions 
 { 
  
 DiscardUnknown 
 : 
  
 true 
 , 
  
 } 
  
 err 
  
 := 
  
 options 
 . 
 Unmarshal 
 ( 
 e 
 . 
  Data 
 
 (), 
  
& data 
 ) 
  
 if 
  
 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

  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#

  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 
 , 
  
 cancellationToken 
 : 
  
 cancellationToken 
 ); 
  
 } 
 }

Deploy the function

To deploy the Convert to Uppercase function, run the following command:

If you haven't already done so, set up your Firestore database .

To deploy the function, see Create triggers for functions .

Test the function

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

In the Google Cloud console, go to the Firestore databases page:

Go to Firestore
Click Start a collection.
Specify messages as the collection ID.
To start adding the collection's first document, under Add its first documentaccept the auto-generated Document ID.
To trigger your deployed function, add a document where the Field nameis original and the Field valueis minka .
When you save the document, you can see the lowercase word in the value field convert to uppercase.

If you subsequently edit the field value to contain lowercase letters, that triggers the function again, converting all lowercase letters to uppercase.

Limitations for 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 might result in multiple function invocations. Avoid depending on exactly-once mechanics, and write idempotent functions .
A trigger is associated with a single database. You can't create a trigger that matches multiple databases.
Deleting a database doesn't automatically delete any triggers for that database. The trigger stops delivering events but continues to exist until you delete the trigger .