Atlas triggers overview in MongoDB - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

What is the primary purpose of an Atlas trigger?

Atlas triggers in MongoDB are used to:

A Create backups of the database on demand

B Manually update documents in the database

C Automatically run functions in response to database events or scheduled times

D Manage user authentication and roles

💡 Hint

Think about what happens automatically when data changes or at specific times.

Atlas triggers automatically execute functions when certain database events occur or on a schedule, enabling automation without manual intervention.

❓ query_result

intermediate

What output does this trigger function produce when a document is inserted?

Consider an Atlas trigger function that logs the inserted document's _id field:

exports = function(changeEvent) {
  const docId = changeEvent.fullDocument._id;
  return `Inserted document ID: ${docId}`;
};

What will be the output if a document with _id value 12345 is inserted?

A Inserted document ID: null

B Inserted document ID: undefined

C Error: fullDocument is not defined

D Inserted document ID: 12345

💡 Hint

The fullDocument field contains the inserted document.

The changeEvent.fullDocument holds the entire inserted document, so accessing _id returns the inserted document's ID.

📝 Syntax

advanced

Which option correctly defines a scheduled trigger to run every hour?

Choose the correct cron expression to schedule an Atlas trigger to run at the start of every hour.

A 0 0 0 * *

B 0 0 * * * *

C 0 * * * *

D 0 0 0 * * *

💡 Hint

Atlas uses 6-field cron expressions: seconds, minutes, hours, day of month, month, day of week.

The correct 6-field cron expression for running at the start of every hour is 0 0 * * * * (0 seconds, 0 minutes, every hour).

❓ optimization

advanced

How to optimize a trigger function that reads and writes to the same collection?

You have an Atlas trigger that listens to inserts and updates the same document in the collection. What is the best way to avoid infinite loops caused by the trigger firing itself?

A Use a field flag in the document to check if the update is from the trigger and skip processing if true

B Disable the trigger before updating and enable it after

C Use a different collection for updates

D Increase the trigger's timeout setting

💡 Hint

Think about how to detect if the trigger caused the update to avoid re-triggering.

Adding a flag field to mark updates done by the trigger lets the function skip processing those updates, preventing infinite loops.

🔧 Debug

expert

What error occurs with this trigger function code?

Analyze this Atlas trigger function:

exports = function(changeEvent) {
  const doc = changeEvent.fullDocument;
  if (doc.status === 'active') {
    return 'Active document';
  } else {
    return 'Inactive document';
  }
};

What error or issue will this code cause when the trigger runs?

A Always returns 'Active document' due to assignment instead of comparison

B SyntaxError because of missing semicolon

C TypeError because fullDocument is undefined

D ReferenceError because 'doc' is not declared

💡 Hint

Check the condition inside the if statement carefully.

The code uses a single equals sign = which assigns 'active' to doc.status instead of comparing it. This makes the condition always true, so it always returns 'Active document'.