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// Copyright 2019 Google LLC
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// See the License for the specific language governing permissions and
// limitations under the License.
// [START functions_firebase_reactive]
// Package upper contains a Firestore Cloud Function.
package upper
import (
firebase ""
// 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: %v", err)
return nil
// [END functions_firebase_reactive]
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