If you are creating a new function, see the Console Quickstart on Cloud Run. The content on this page only applies to existing legacy functions created with the Cloud Functions v1 API.

Google Cloud Firestore triggers (1st gen)

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

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

Waits for changes to a particular document.
Triggers when an event occurs and performs its tasks.
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

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

Event type	Trigger
`providers/cloud.firestore/eventTypes/document.create` (default)	Triggered when a document is written to for the first time.
`providers/cloud.firestore/eventTypes/document.update`	Triggered when a document already exists and has any value changed.
`providers/cloud.firestore/eventTypes/document.delete`	Triggered when a document with data is deleted.
`providers/cloud.firestore/eventTypes/document.write`	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.

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.

Wildcard matches are extracted from document paths. You can define as many wildcards as you like to substitute explicit collection or document IDs.

Event structure

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

 { 
  
 "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. This is especially useful if you're using a typed language (like Go) to write your functions.

Code sample

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

Node.js

  /** 
 * Background Function triggered by a change to a Firestore document. 
 * 
 * @param {!Object} event The Cloud Functions event. 
 * @param {!Object} context Cloud Functions event metadata. 
 */ 
 exports 
 . 
 helloFirestore 
  
 = 
  
 ( 
 event 
 , 
  
 context 
 ) 
  
 = 
>  
 { 
  
 const 
  
 triggerResource 
  
 = 
  
 context 
 . 
 resource 
 ; 
  
 console 
 . 
 log 
 ( 
 `Function triggered by event on: 
 ${ 
 triggerResource 
 } 
 ` 
 ); 
  
 console 
 . 
 log 
 ( 
 `Event type: 
 ${ 
 context 
 . 
 eventType 
 } 
 ` 
 ); 
  
 if 
  
 ( 
 event 
 . 
 oldValue 
 && 
 Object 
 . 
 keys 
 ( 
 event 
 . 
 oldValue 
 ). 
 length 
 ) 
  
 { 
  
 console 
 . 
 log 
 ( 
 '\nOld value:' 
 ); 
  
 console 
 . 
 log 
 ( 
 JSON 
 . 
 stringify 
 ( 
 event 
 . 
 oldValue 
 , 
  
 null 
 , 
  
 2 
 )); 
  
 } 
  
 if 
  
 ( 
 event 
 . 
 value 
 && 
 Object 
 . 
 keys 
 ( 
 event 
 . 
 value 
 ). 
 length 
 ) 
  
 { 
  
 console 
 . 
 log 
 ( 
 '\nNew value:' 
 ); 
  
 console 
 . 
 log 
 ( 
 JSON 
 . 
 stringify 
 ( 
 event 
 . 
 value 
 , 
  
 null 
 , 
  
 2 
 )); 
  
 } 
 };

Python

  import 
  
 json 
 def 
  
 hello_firestore 
 ( 
 data 
 , 
 context 
 ): 
  
 """Triggered by a change to a Firestore document. 
 Args: 
 data (dict): The event payload. 
 context (google.cloud.functions.Context): Metadata for the event. 
 """ 
 trigger_resource 
 = 
 context 
 . 
 resource 
 print 
 ( 
 "Function triggered by change to: 
 %s 
 " 
 % 
 trigger_resource 
 ) 
 print 
 ( 
 " 
 \n 
 Old value:" 
 ) 
 print 
 ( 
 json 
 . 
 dumps 
 ( 
 data 
 [ 
 "oldValue" 
 ])) 
 print 
 ( 
 " 
 \n 
 New value:" 
 ) 
 print 
 ( 
 json 
 . 
 dumps 
 ( 
 data 
 [ 
 "value" 
 ]))

Go

  // Package hello contains a Cloud Function triggered by a Firestore event. 
 package 
  
 hello 
 import 
  
 ( 
  
 "context" 
  
 "fmt" 
  
 "log" 
  
 "time" 
  
 "cloud.google.com/go/functions/metadata" 
 ) 
 // FirestoreEvent is the payload of a Firestore event. 
 type 
  
 FirestoreEvent 
  
 struct 
  
 { 
  
 OldValue 
  
 FirestoreValue 
  
 `json:"oldValue"` 
  
 Value 
  
 FirestoreValue 
  
 `json:"value"` 
  
 UpdateMask 
  
 struct 
  
 { 
  
 FieldPaths 
  
 [] 
 string 
  
 `json:"fieldPaths"` 
  
 } 
  
 `json:"updateMask"` 
 } 
 // FirestoreValue holds Firestore fields. 
 type 
  
 FirestoreValue 
  
 struct 
  
 { 
  
 CreateTime 
  
 time 
 . 
 Time 
  
 `json:"createTime"` 
  
 // Fields is the data for this value. The type depends on the format of your 
  
 // database. Log the interface{} value and inspect the result to see a JSON 
  
 // representation of your database fields. 
  
 Fields 
  
 interface 
 {} 
  
 `json:"fields"` 
  
 Name 
  
 string 
  
 `json:"name"` 
  
 UpdateTime 
  
 time 
 . 
 Time 
  
 `json:"updateTime"` 
 } 
 // HelloFirestore is triggered by a change to a Firestore document. 
 func 
  
 HelloFirestore 
 ( 
 ctx 
  
 context 
 . 
 Context 
 , 
  
 e 
  
 FirestoreEvent 
 ) 
  
 error 
  
 { 
  
 meta 
 , 
  
 err 
  
 := 
  
 metadata 
 . 
  FromContext 
 
 ( 
 ctx 
 ) 
  
 if 
  
 err 
  
 != 
  
 nil 
  
 { 
  
 return 
  
 fmt 
 . 
 Errorf 
 ( 
 "metadata.FromContext: %w" 
 , 
  
 err 
 ) 
  
 } 
  
 log 
 . 
 Printf 
 ( 
 "Function triggered by change to: %v" 
 , 
  
 meta 
 . 
  Resource 
 
 ) 
  
 log 
 . 
 Printf 
 ( 
 "Old value: %+v" 
 , 
  
 e 
 . 
 OldValue 
 ) 
  
 log 
 . 
 Printf 
 ( 
 "New value: %+v" 
 , 
  
 e 
 . 
 Value 
 ) 
  
 return 
  
 nil 
 }

Java

  import 
  
 com.google.cloud.functions.Context 
 ; 
 import 
  
 com.google.cloud.functions.RawBackgroundFunction 
 ; 
 import 
  
 com.google.gson.Gson 
 ; 
 import 
  
 com.google.gson.JsonObject 
 ; 
 import 
  
 java.util.logging.Logger 
 ; 
 public 
  
 class 
 FirebaseFirestore 
  
 implements 
  
 RawBackgroundFunction 
  
 { 
  
 private 
  
 static 
  
 final 
  
 Logger 
  
 logger 
  
 = 
  
 Logger 
 . 
 getLogger 
 ( 
 FirebaseFirestore 
 . 
 class 
 . 
 getName 
 ()); 
  
 // Use GSON (https://github.com/google/gson) to parse JSON content. 
  
 private 
  
 static 
  
 final 
  
 Gson 
  
 gson 
  
 = 
  
 new 
  
 Gson 
 (); 
  
 @Override 
  
 public 
  
 void 
  
 accept 
 ( 
 String 
  
 json 
 , 
  
 Context 
  
 context 
 ) 
  
 { 
  
 JsonObject 
  
 body 
  
 = 
  
 gson 
 . 
 fromJson 
 ( 
 json 
 , 
  
 JsonObject 
 . 
 class 
 ); 
  
 logger 
 . 
 info 
 ( 
 "Function triggered by event on: " 
  
 + 
  
 context 
 . 
 resource 
 ()); 
  
 logger 
 . 
 info 
 ( 
 "Event type: " 
  
 + 
  
 context 
 . 
 eventType 
 ()); 
  
 if 
  
 ( 
 body 
  
 != 
  
 null 
 && 
 body 
 . 
 has 
 ( 
 "oldValue" 
 )) 
  
 { 
  
 logger 
 . 
 info 
 ( 
 "Old value:" 
 ); 
  
 logger 
 . 
 info 
 ( 
 body 
 . 
 get 
 ( 
 "oldValue" 
 ). 
 getAsString 
 ()); 
  
 } 
  
 if 
  
 ( 
 body 
  
 != 
  
 null 
 && 
 body 
 . 
 has 
 ( 
 "value" 
 )) 
  
 { 
  
 logger 
 . 
 info 
 ( 
 "New value:" 
 ); 
  
 logger 
 . 
 info 
 ( 
 body 
 . 
 get 
 ( 
 "value" 
 ). 
 getAsString 
 ()); 
  
 } 
  
 } 
 }

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 
 )); 
  
 } 
 }

Ruby

  require 
  
 "functions_framework" 
 # Triggered by a change to a Firestore document. 
 FunctionsFramework 
 . 
 cloud_event 
  
 "hello_firestore" 
  
 do 
  
 | 
 event 
 | 
  
 # The event parameter is a CloudEvents::Event::V1 object. 
  
 # See https://cloudevents.github.io/sdk-ruby/latest/CloudEvents/Event/V1.html 
  
 payload 
  
 = 
  
 event 
 . 
 data 
  
 logger 
 . 
 info 
  
 "Function triggered by change to: 
 #{ 
 event 
 . 
 source 
 } 
 " 
  
 logger 
 . 
 info 
  
 "Old value: 
 #{ 
 payload 
 [ 
 'oldValue' 
 ] 
 } 
 " 
  
 logger 
 . 
 info 
  
 "New value: 
 #{ 
 payload 
 [ 
 'value' 
 ] 
 } 
 " 
 end

PHP

 use Google\CloudFunctions\CloudEvent; 
 function firebaseFirestore(CloudEvent $cloudevent) 
 { 
 $log = fopen(getenv('LOGGER_OUTPUT') ?: 'php://stderr', 'wb'); 
 fwrite($log, 'Event: ' . $cloudevent->getId() . PHP_EOL); 
 fwrite($log, 'Event Type: ' . $cloudevent->getType() . PHP_EOL); 
 $data = $cloudevent->getData(); 
 $resource = $data['resource']; 
 fwrite($log, 'Function triggered by event on: ' . $resource . PHP_EOL); 
 if (isset($data['oldValue'])) { 
 fwrite($log, 'Old value: ' . json_encode($data['oldValue']) . PHP_EOL); 
 } 
 if (isset($data['value'])) { 
 fwrite($log, 'New value: ' . json_encode($data['value']) . PHP_EOL); 
 } 
 }

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

  const 
  
 Firestore 
  
 = 
  
 require 
 ( 
 ' @google-cloud/firestore 
' 
 ); 
 const 
  
 firestore 
  
 = 
  
 new 
  
  Firestore 
 
 ({ 
  
 projectId 
 : 
  
 process 
 . 
 env 
 . 
 GOOGLE_CLOUD_PROJECT 
 , 
 }); 
 // Converts strings added to /messages/{pushId}/original to uppercase 
 exports 
 . 
 makeUpperCase 
  
 = 
  
 event 
  
 = 
>  
 { 
  
 const 
  
 resource 
  
 = 
  
 event 
 . 
 value 
 . 
 name 
 ; 
  
 const 
  
 affectedDoc 
  
 = 
  
 firestore 
 . 
 doc 
 ( 
 resource 
 . 
 split 
 ( 
 '/documents/' 
 )[ 
 1 
 ]); 
  
 const 
  
 curValue 
  
 = 
  
 event 
 . 
 value 
 . 
 fields 
 . 
 original 
 . 
 stringValue 
 ; 
  
 const 
  
 newValue 
  
 = 
  
 curValue 
 . 
 toUpperCase 
 (); 
  
 if 
  
 ( 
 curValue 
  
 !== 
  
 newValue 
 ) 
  
 { 
  
 console 
 . 
 log 
 ( 
 `Replacing value: 
 ${ 
 curValue 
 } 
 --> 
 ${ 
 newValue 
 } 
 ` 
 ); 
  
 return 
  
 affectedDoc 
 . 
 set 
 ({ 
  
 original 
 : 
  
 newValue 
 , 
  
 }); 
  
 } 
  
 else 
  
 { 
  
 // Value is already upper-case 
  
 // Don't perform a(nother) write to avoid infinite loops 
  
 console 
 . 
 log 
 ( 
 'Value is already upper-case.' 
 ); 
  
 } 
 };

Python

  from 
  
 google.cloud 
  
 import 
 firestore 
 client 
 = 
 firestore 
 . 
  Client 
 
 () 
 # Converts strings added to /messages/{pushId}/original to uppercase 
 def 
  
 make_upper_case 
 ( 
 data 
 , 
 context 
 ): 
 path_parts 
 = 
 context 
 . 
 resource 
 . 
 split 
 ( 
 "/documents/" 
 )[ 
 1 
 ] 
 . 
 split 
 ( 
 "/" 
 ) 
 collection_path 
 = 
 path_parts 
 [ 
 0 
 ] 
 document_path 
 = 
 "/" 
 . 
 join 
 ( 
 path_parts 
 [ 
 1 
 :]) 
 affected_doc 
 = 
 client 
 . 
  collection 
 
 ( 
 collection_path 
 ) 
 . 
 document 
 ( 
 document_path 
 ) 
 cur_value 
 = 
 data 
 [ 
 "value" 
 ][ 
 "fields" 
 ][ 
 "original" 
 ][ 
 "stringValue" 
 ] 
 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" 
  
 "fmt" 
  
 "log" 
  
 "os" 
  
 "strings" 
  
 "time" 
  
 "cloud.google.com/go/firestore" 
  
 firebase 
  
 "firebase.google.com/go/v4" 
 ) 
 // FirestoreEvent is the payload of a Firestore event. 
 type 
  
 FirestoreEvent 
  
 struct 
  
 { 
  
 OldValue 
  
 FirestoreValue 
  
 `json:"oldValue"` 
  
 Value 
  
 FirestoreValue 
  
 `json:"value"` 
  
 UpdateMask 
  
 struct 
  
 { 
  
 FieldPaths 
  
 [] 
 string 
  
 `json:"fieldPaths"` 
  
 } 
  
 `json:"updateMask"` 
 } 
 // FirestoreValue holds Firestore fields. 
 type 
  
 FirestoreValue 
  
 struct 
  
 { 
  
 CreateTime 
  
 time 
 . 
 Time 
  
 `json:"createTime"` 
  
 // Fields is the data for this value. The type depends on the format of your 
  
 // database. Log an interface{} value and inspect the result to see a JSON 
  
 // representation of your database fields. 
  
 Fields 
  
 MyData 
  
 `json:"fields"` 
  
 Name 
  
 string 
  
 `json:"name"` 
  
 UpdateTime 
  
 time 
 . 
 Time 
  
 `json:"updateTime"` 
 } 
 // MyData represents a value from Firestore. The type definition depends on the 
 // format of your database. 
 type 
  
 MyData 
  
 struct 
  
 { 
  
 Original 
  
 struct 
  
 { 
  
 StringValue 
  
 string 
  
 `json:"stringValue"` 
  
 } 
  
 `json:"original"` 
 } 
 // GOOGLE_CLOUD_PROJECT is automatically set by the Cloud Functions runtime. 
 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 
 ) 
  
 } 
 } 
 // 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 
  
 FirestoreEvent 
 ) 
  
 error 
  
 { 
  
 fullPath 
  
 := 
  
 strings 
 . 
 Split 
 ( 
 e 
 . 
  Value 
 
 . 
 Name 
 , 
  
 "/documents/" 
 )[ 
 1 
 ] 
  
 pathParts 
  
 := 
  
 strings 
 . 
 Split 
 ( 
 fullPath 
 , 
  
 "/" 
 ) 
  
 collection 
  
 := 
  
 pathParts 
 [ 
 0 
 ] 
  
 doc 
  
 := 
  
 strings 
 . 
 Join 
 ( 
 pathParts 
 [ 
 1 
 :], 
  
 "/" 
 ) 
  
 curValue 
  
 := 
  
 e 
 . 
  Value 
 
 . 
 Fields 
 . 
 Original 
 . 
 StringValue 
  
 newValue 
  
 := 
  
 strings 
 . 
 ToUpper 
 ( 
 curValue 
 ) 
  
 if 
  
 curValue 
  
 == 
  
 newValue 
  
 { 
  
 log 
 . 
 Printf 
 ( 
 "%q is already upper case: skipping" 
 , 
  
 curValue 
 ) 
  
 return 
  
 nil 
  
 } 
  
 log 
 . 
 Printf 
 ( 
 "Replacing value: %q -> %q" 
 , 
  
 curValue 
 , 
  
 newValue 
 ) 
  
 data 
  
 := 
  
 map 
 [ 
 string 
 ] 
 string 
 { 
 "original" 
 : 
  
 newValue 
 } 
  
 _ 
 , 
  
 err 
  
 := 
  
 client 
 . 
 Collection 
 ( 
 collection 
 ). 
 Doc 
 ( 
 doc 
 ). 
 Set 
 ( 
 ctx 
 , 
  
 data 
 ) 
  
 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. Context 
 
 ; 
 import 
  
 com.google.cloud.functions.RawBackgroundFunction 
 ; 
 import 
  
 com.google.gson.Gson 
 ; 
 import 
  
 com.google.gson.JsonObject 
 ; 
 import 
  
 java.util.HashMap 
 ; 
 import 
  
 java.util.Locale 
 ; 
 import 
  
 java.util.Map 
 ; 
 import 
  
 java.util.concurrent.ExecutionException 
 ; 
 import 
  
 java.util.logging.Level 
 ; 
 import 
  
 java.util.logging.Logger 
 ; 
 public 
  
 class 
 FirebaseFirestoreReactive 
  
 implements 
  
 RawBackgroundFunction 
  
 { 
  
 // Use GSON (https://github.com/google/gson) to parse JSON content. 
  
 private 
  
 static 
  
 final 
  
 Gson 
  
 gson 
  
 = 
  
 new 
  
 Gson 
 (); 
  
 private 
  
 static 
  
 final 
  
 Logger 
  
 logger 
  
 = 
  
 Logger 
 . 
 getLogger 
 ( 
 FirebaseFirestoreReactive 
 . 
 class 
 . 
 getName 
 ()); 
  
 private 
  
 static 
  
 final 
  
  Firestore 
 
  
 FIRESTORE 
  
 = 
  
  FirestoreOptions 
 
 . 
 getDefaultInstance 
 (). 
 getService 
 (); 
  
 private 
  
 final 
  
  Firestore 
 
  
 firestore 
 ; 
  
 public 
  
 FirebaseFirestoreReactive 
 () 
  
 { 
  
 this 
 ( 
 FIRESTORE 
 ); 
  
 } 
  
 FirebaseFirestoreReactive 
 ( 
  Firestore 
 
  
 firestore 
 ) 
  
 { 
  
 this 
 . 
 firestore 
  
 = 
  
 firestore 
 ; 
  
 } 
  
 @Override 
  
 public 
  
 void 
  
 accept 
 ( 
 String 
  
 json 
 , 
  
  Context 
 
  
 context 
 ) 
  
 { 
  
 // Get the recently-written value 
  
 JsonObject 
  
 body 
  
 = 
  
 gson 
 . 
 fromJson 
 ( 
 json 
 , 
  
 JsonObject 
 . 
 class 
 ); 
  
 JsonObject 
  
 tempJson 
  
 = 
  
 body 
 . 
 getAsJsonObject 
 ( 
 "value" 
 ); 
  
 // Verify that value.fields.original.stringValue exists 
  
 String 
  
 currentValue 
  
 = 
  
 null 
 ; 
  
 if 
  
 ( 
 tempJson 
  
 != 
  
 null 
 ) 
  
 { 
  
 tempJson 
  
 = 
  
 tempJson 
 . 
 getAsJsonObject 
 ( 
 "fields" 
 ); 
  
 } 
  
 if 
  
 ( 
 tempJson 
  
 != 
  
 null 
 ) 
  
 { 
  
 tempJson 
  
 = 
  
 tempJson 
 . 
 getAsJsonObject 
 ( 
 "original" 
 ); 
  
 } 
  
 if 
  
 ( 
 tempJson 
  
 != 
  
 null 
 && 
 tempJson 
 . 
 has 
 ( 
 "stringValue" 
 )) 
  
 { 
  
 currentValue 
  
 = 
  
 tempJson 
 . 
 get 
 ( 
 "stringValue" 
 ). 
 getAsString 
 (); 
  
 } 
  
 if 
  
 ( 
 currentValue 
  
 == 
  
 null 
 ) 
  
 { 
  
 throw 
  
 new 
  
 IllegalArgumentException 
 ( 
 "Malformed JSON: " 
  
 + 
  
 json 
 ); 
  
 } 
  
 // Convert recently-written value to ALL CAPS 
  
 String 
  
 newValue 
  
 = 
  
 currentValue 
 . 
 toUpperCase 
 ( 
 Locale 
 . 
 getDefault 
 ()); 
  
 // Update Firestore DB with ALL CAPS value 
  
 Map<String 
 , 
  
 String 
>  
 newFields 
  
 = 
  
 Map 
 . 
 of 
 ( 
 "original" 
 , 
  
 newValue 
 ); 
  
 String 
  
 affectedDoc 
  
 = 
  
 context 
 . 
 resource 
 (). 
 split 
 ( 
 "/documents/" 
 ) 
 [ 
 1 
 ] 
 . 
 replace 
 ( 
 "\"" 
 , 
  
 "" 
 ); 
  
 if 
  
 ( 
 ! 
 currentValue 
 . 
 equals 
 ( 
 newValue 
 )) 
  
 { 
  
 // The stored value needs to be updated 
  
 // Write the upper-cased value to Firestore 
  
  logger 
 
 . 
 info 
 ( 
 String 
 . 
 format 
 ( 
 "Replacing value: %s --> %s" 
 , 
  
 currentValue 
 , 
  
 newValue 
 )); 
  
 try 
  
 { 
  
 FIRESTORE 
 . 
  document 
 
 ( 
 affectedDoc 
 ). 
 set 
 ( 
 newFields 
 , 
  
  SetOptions 
 
 . 
  merge 
 
 ()). 
 get 
 (); 
  
 } 
  
 catch 
  
 ( 
 ExecutionException 
  
 | 
  
 InterruptedException 
  
 e 
 ) 
  
 { 
  
  logger 
 
 . 
 log 
 ( 
 Level 
 . 
 SEVERE 
 , 
  
 "Error updating Firestore document: " 
  
 + 
  
 e 
 . 
 getMessage 
 (), 
  
 e 
 ); 
  
 } 
  
 } 
  
 else 
  
 { 
  
 // The stored value is already upper-case, and doesn't need updating. 
  
 // (Don't perform a "second" write, since that could trigger an infinite loop.) 
  
  logger 
 
 . 
 info 
 ( 
 String 
 . 
 format 
 ( 
 "Value is already upper-case." 
 )); 
  
 } 
  
 } 
 }

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 
 ); 
  
 } 
 }

Ruby

  require 
  
 "functions_framework" 
 FunctionsFramework 
 . 
 on_startup 
  
 do 
  
 # Lazily construct a Firestore client when needed, and reuse it on 
  
 # subsequent calls. 
  
 set_global 
  
 :firestore_client 
  
 do 
  
 require 
  
 "google/cloud/firestore" 
  
 Google 
 :: 
 Cloud 
 :: 
  Firestore 
 
 . 
  new 
 
  
 project_id 
 : 
  
 ENV 
 [ 
 "GOOGLE_CLOUD_PROJECT" 
 ] 
  
 end 
 end 
 # Converts strings added to /messages/{pushId}/original to uppercase 
 FunctionsFramework 
 . 
 cloud_event 
  
 "make_upper_case" 
  
 do 
  
 | 
 event 
 | 
  
 # Event-triggered Ruby functions receive a CloudEvents::Event::V1 object. 
  
 # See https://cloudevents.github.io/sdk-ruby/latest/CloudEvents/Event/V1.html 
  
 # The Firebase event payload can be obtained from the event data. 
  
 cur_value 
  
 = 
  
 event 
 . 
  data 
 
 [ 
 "value" 
 ][ 
 "fields" 
 ][ 
 "original" 
 ][ 
 "stringValue" 
 ] 
  
 # Compute new value and determine whether it needs to be modified. 
  
 # If the value is already upper-case, don't perform another write, 
  
 # to avoid infinite loops. 
  
 new_value 
  
 = 
  
 cur_value 
 . 
 upcase 
  
 if 
  
 cur_value 
  
 == 
  
 new_value 
  
 logger 
 . 
 info 
  
 "Value is already upper-case" 
  
 return 
  
 end 
  
 # Use the Firestore client library to update the value. 
  
 # The document name can be obtained from the event subject. 
  
 logger 
 . 
 info 
  
 "Replacing value: 
 #{ 
 cur_value 
 } 
 --> 
 #{ 
 new_value 
 } 
 " 
  
 doc_name 
  
 = 
  
 event 
 . 
 subject 
 . 
 split 
 ( 
 "documents/" 
 ) 
 . 
 last 
  
 affected_doc 
  
 = 
  
 global 
 ( 
 :firestore_client 
 ) 
 . 
 doc 
  
 doc_name 
  
 new_doc_data 
  
 = 
  
 { 
  
 original 
 : 
  
 new_value 
  
 } 
  
 affected_doc 
 . 
 set 
  
 new_doc_data 
 , 
  
 merge 
 : 
  
 false 
 end

PHP

 use Google\Cloud\Firestore\FirestoreClient; 
 use Google\CloudFunctions\CloudEvent; 
 function firebaseReactive(CloudEvent $cloudevent) 
 { 
 $log = fopen(getenv('LOGGER_OUTPUT') ?: 'php://stderr', 'wb'); 
 $data = $cloudevent->getData(); 
 $resource = $data['value']['name']; 
 $db = new FirestoreClient(); 
 $docPath = explode('/documents/', $resource)[1]; 
 $affectedDoc = $db->document($docPath); 
 $curValue = $data['value']['fields']['original']['stringValue']; 
 $newValue = strtoupper($curValue); 
 if ($curValue !== $newValue) { 
 fwrite($log, 'Replacing value: ' . $curValue . ' --> ' . $newValue . PHP_EOL); 
 $affectedDoc->set(['original' => $newValue]); 
 } else { 
 // Value is already upper-case 
 // Don't perform another write (it might cause an infinite loop) 
 fwrite($log, 'Value is already upper-case.' . PHP_EOL); 
 } 
 }

Deploying your function

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

gcloud  
functions  
deploy  
 FUNCTION_NAME 
  
 \ 
  
--no-gen2  
 \ 
  
--entry-point  
 ENTRY_POINT 
  
 \ 
  
--runtime  
 RUNTIME 
  
 \ 
  
--set-env-vars  
 GOOGLE_CLOUD_PROJECT 
 = 
 YOUR_PROJECT_ID 
  
 \ 
  
--trigger-event  
 "providers/cloud.firestore/eventTypes/document.write" 
  
 \ 
  
--trigger-resource  
 "projects/ YOUR_PROJECT_ID 
/databases/(default)/documents/messages/{pushId}"

Argument	Description
`FUNCTION_NAME`	The registered name of the Cloud Function you are deploying. This can either be the name of a function in your source code, or an arbitrary string. If `FUNCTION_NAME` is an arbitrary string, then you must include the `--entry-point` flag.
`--entry-point ENTRY_POINT`	The name of a function or class in your source code. Optional, unless you did not use `FUNCTION_NAME` to specify the function in your source code to be executed during deployment. In that case, you must use `--entry-point` to supply the name of the executable function.
`--runtime RUNTIME`	The name of the runtime you are using. For a complete list, see the `gcloud` reference .
`--set-env-vars GOOGLE_CLOUD_PROJECT= YOUR_PROJECT_ID`	The unique identifier of the project as a runtime environment variable.
`--trigger-event NAME`	The event type that the function will monitor for (one of `write` , `create` , `update` or `delete` ).
`--trigger-resource NAME`	The fully qualified database path to which the function will listen. This should conform to the following format: `"projects/ YOUR_PROJECT_ID /databases/(default)/documents/ PATH "` The `{pushId}` text is a wildcard parameter described above in Specifying the document path .

Limitations

Note the following limitations for Firestore triggers for Cloud Run functions:

Cloud Run functions (1st gen) prerequisites an existing "(default)" database in Firestore native mode. It does not support Firestore named databases or Datastore mode. Please use Cloud Run functions (2nd gen) to configure events in such cases.
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 in Datastore mode requires Cloud Run functions (2nd gen). Cloud Run functions (1st gen) does not support Datastore mode.
A trigger is associated with a single database. You cannot create a trigger that matches multiple databases.
Deleting a database does not automatically delete any triggers for that database. The trigger stops delivering events but continues to exist until you delete the trigger .
If a matched event exceeds the maximum request size , the event might not be delivered to Cloud Run functions (1st gen).
- Events not delivered because of request size are logged in platform logs and count towards the log usage for the project.
- You can find these logs in the Logs Explorer with the message "Event cannot deliver to Cloud function due to size exceeding the limit for 1st gen..." of error severity. You can find the function name under the functionName field. If the receiveTimestamp field is still within an hour from now, you can infer the actual event content by reading the document in question with a snapshot before and after the timestamp.
- To avoid such cadence, you can:
  - Migrate and upgrade to Cloud Run functions (2nd gen)
  - Downsize the document
  - Delete the Cloud Run functions in question
- You can turn off the logging itself using exclusions but note that the offending events will still not be delivered.