Triggers (onCreate/onWrite)Advanced
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typescriptHow do Firestore background triggers (onCreate, onUpdate, onDelete) operate in Cloud Functions?
Explanation & Concept
Firestore background triggers execute asynchronously on Google Cloud whenever a document in a specified collection path is created, modified, or deleted.
• `onDocumentCreated`: Triggers when a new document is inserted. • `onDocumentUpdated`: Provides `event.data.before` and `event.data.after` snapshots. • `onDocumentDeleted`: Triggers when a document is deleted.
Code Example
typescript
import { onDocumentCreated } from "firebase-functions/v2/firestore";
import { getFirestore } from "firebase-admin/firestore";
export const sendWelcomeEmailOnUserCreated = onDocumentCreated(
"users/{userId}",
async (event) => {
const newUser = event.data.data();
console.log("New user registered:", newUser.email);
// Add an audit log or trigger welcome email service
const db = getFirestore();
await db.collection("mail_queue").add({
to: newUser.email,
template: "welcome_email",
sentAt: new Date()
});
}
);How It Works & Key Takeaways
Background triggers ensure event-driven decoupling: creating a user document automatically triggers secondary asynchronous workflows like email sending or audit logging.
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