MongoDB Atlas Triggers

Automate actions based on database events

⚡ What are Atlas Triggers?

Atlas Triggers automatically execute server-side logic in response to database changes or scheduled events. They help automate workflows, send notifications, and sync data without writing complex backend code. 


// Database Trigger Example
exports = function(changeEvent) {
  const doc = changeEvent.fullDocument;
  console.log("New user created:", doc.name);
};

Output:

New user created: John Doe

Types of Triggers

🔄

Database Triggers

React to insert, update, or delete operations 

// On document insert
exports = function(changeEvent) {
  const newDoc = changeEvent.fullDocument;
  // Process new document
};
⏰

Scheduled Triggers

Run functions at specific times or intervals 

// Runs every day at midnight
exports = function() {
  console.log("Daily cleanup task");
};
🔔

Authentication Triggers

Execute logic on user authentication events 

// On user creation
exports = function(authEvent) {
  const user = authEvent.user;
  console.log("Welcome:", user.id);
};
📧

Event Processing

Send emails, notifications, or webhooks 

// Send notification
exports = function(changeEvent) {
  // Send email or push notification
  return { status: "sent" };
};

🔹 Creating a Database Trigger

Database triggers respond to changes in your MongoDB collections. They execute automatically when documents are inserted, updated, or deleted, enabling real-time data processing and automation. 

// Trigger Configuration
{
  "name": "onNewOrder",
  "type": "DATABASE",
  "config": {
    "operation_types": ["insert"],
    "database": "store",
    "collection": "orders"
  }
}

// Trigger Function
exports = async function(changeEvent) {
  const order = changeEvent.fullDocument;
  
  // Send confirmation email
  console.log(`Order ${order._id} received`);
  console.log(`Total: $${order.total}`);
  
  // Update inventory
  const mongodb = context.services.get("mongodb-atlas");
  const inventory = mongodb.db("store").collection("inventory");
  
  await inventory.updateOne(
    { _id: order.productId },
    { $inc: { stock: -order.quantity } }
  );
};

Output:

Order 507f1f77bcf86cd799439011 received

Total: $49.99

🔹 Creating a Scheduled Trigger

Scheduled triggers run functions at specific times or intervals using CRON expressions. Perfect for daily reports, cleanup tasks, data synchronization, or any recurring automation needs. 

// Trigger Configuration
{
  "name": "dailyReport",
  "type": "SCHEDULED",
  "config": {
    "schedule": "0 0 * * *"  // Every day at midnight
  }
}

// Trigger Function
exports = async function() {
  const mongodb = context.services.get("mongodb-atlas");
  const orders = mongodb.db("store").collection("orders");
  
  // Get yesterday's date
  const yesterday = new Date();
  yesterday.setDate(yesterday.getDate() - 1);
  
  // Count orders from yesterday
  const count = await orders.countDocuments({
    createdAt: { $gte: yesterday }
  });
  
  console.log(`Daily Report: ${count} orders processed`);
  
  // Send report email or notification
  return { ordersProcessed: count };
};

Output:

Daily Report: 127 orders processed

🔹 Common CRON Schedules

CRON expressions define when scheduled triggers run:

  • * * * * * - Every minute
  • 0 * * * * - Every hour
  • 0 0 * * * - Every day at midnight
  • 0 9 * * 1 - Every Monday at 9 AM
  • 0 0 1 * * - First day of every month

🔹 Accessing Change Events

Change events provide detailed information about database operations. You can access the full document, operation type, and modified fields to build sophisticated automation logic. 

exports = function(changeEvent) {
  // Operation type: insert, update, delete, replace
  const operationType = changeEvent.operationType;
  
  // Full document (for insert/replace)
  const fullDocument = changeEvent.fullDocument;
  
  // Document ID
  const documentId = changeEvent.documentKey._id;
  
  // Updated fields (for update operations)
  const updatedFields = changeEvent.updateDescription?.updatedFields;
  
  console.log(`Operation: ${operationType}`);
  console.log(`Document ID: ${documentId}`);
  
  if (operationType === "update") {
    console.log("Updated fields:", updatedFields);
  }
};

🔹 Best Practices

Follow these guidelines for reliable triggers:

  • Keep functions fast: Triggers should execute quickly (under 90 seconds)
  • Handle errors: Use try-catch blocks to prevent failures
  • Use filters: Only trigger on specific conditions to reduce executions
  • Test thoroughly: Test triggers in development before production
  • Monitor logs: Check trigger execution logs regularly

🧠 Test Your Knowledge

What type of trigger runs at specific times or intervals?