Atlas triggers overview in MongoDB - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is an Atlas Trigger in MongoDB?

An Atlas Trigger is a feature in MongoDB Atlas that automatically runs server-side functions in response to database events or on a schedule.

beginner

Name the two main types of Atlas Triggers.

The two main types are:
1. Database Triggers - run when data changes in the database.
2. Scheduled Triggers - run at specified times or intervals.

intermediate

How does a Database Trigger decide when to run?

A Database Trigger runs when a specified operation happens on a collection, such as insert, update, replace, or delete.

beginner

What is a common use case for Scheduled Triggers?

Scheduled Triggers are often used for tasks like cleaning up old data, sending notifications, or running reports at regular intervals.

intermediate

Can Atlas Triggers run custom JavaScript code? Explain.

Yes, Atlas Triggers run custom JavaScript functions in the cloud, allowing you to define exactly what happens when the trigger fires.

What event type can a Database Trigger NOT respond to?

A User login

B Update

C Delete

D Insert

Database Triggers respond to data changes like insert, update, and delete, but not to user login events.

Which Atlas Trigger type runs based on a time schedule?

A Database Trigger

B Scheduled Trigger

C Change Stream Trigger

D Manual Trigger

Scheduled Triggers run at specified times or intervals, unlike Database Triggers which respond to data changes.

What language do Atlas Triggers use for their functions?

A Java

B Python

C SQL

D JavaScript

Atlas Triggers run custom JavaScript functions in the cloud.

Which of these is a valid use case for an Atlas Trigger?

A Manually backup data

B Change the database schema

C Automatically update a document after insert

D Edit user interface

Atlas Triggers can automate actions like updating documents after inserts.

Where do Atlas Triggers run their code?

A On the MongoDB Atlas cloud servers

B On the client device

C On a local server

D In the browser

Atlas Triggers run server-side code on MongoDB Atlas cloud servers.

Explain what Atlas Triggers are and describe the two main types.

Think about when and why triggers run.

Describe a practical example of how you might use a Scheduled Trigger in MongoDB Atlas.

Consider repetitive tasks that happen regularly.

Practice

1. What is the main purpose of an Atlas trigger in MongoDB?

easy

A. To create new collections in the database

B. To manually update documents in a collection

C. To backup the database automatically

D. To automatically run code when certain database events happen

Solution

1. Step 1: Understand what triggers do

   Atlas triggers run code automatically when specific events occur in the database, like inserts or updates.

2. Step 2: Compare options with this purpose

   Only To automatically run code when certain database events happen describes automatic code running on database events, which matches the trigger's purpose.

3. Final Answer:

   To automatically run code when certain database events happen -> Option D

4. Quick Check:

   Atlas triggers = automatic code on events [OK]

Hint: Triggers run code automatically on database events [OK]

Common Mistakes:

• Thinking triggers are for manual updates
• Confusing triggers with backups
• Assuming triggers create collections

2. Which of the following is the correct way to define a function for an Atlas trigger?

easy

A. function triggerFunction() { console.log('Triggered'); }

B. def triggerFunction(): print('Triggered')

C. triggerFunction() => { console.log('Triggered'); }

D. func triggerFunction() { print('Triggered') }

Solution

1. Step 1: Identify the language used in Atlas triggers

   Atlas triggers use JavaScript functions to define actions.

2. Step 2: Check which option is valid JavaScript function syntax

   function triggerFunction() { console.log('Triggered'); } uses standard JavaScript function syntax. Options A and D use Python and Go syntax, and C is invalid arrow function syntax.

3. Final Answer:

   function triggerFunction() { console.log('Triggered'); } -> Option A

4. Quick Check:

   Atlas triggers use JavaScript functions [OK]

Hint: Atlas triggers use JavaScript function syntax [OK]

Common Mistakes:

• Using Python or other language syntax
• Incorrect arrow function syntax
• Missing function keyword in JavaScript

3. Given this Atlas trigger function, what will be logged when a new document is inserted?

exports = function(changeEvent) {
  console.log('Document inserted with _id:', changeEvent.fullDocument._id);
};

medium

A. Document inserted with _id: [actual document _id]

B. No output because console.log is not supported

C. Error: changeEvent is not defined

D. Document inserted with _id: undefined

Solution

1. Step 1: Understand the changeEvent object in insert triggers

   When a document is inserted, changeEvent.fullDocument contains the new document, including its _id.

2. Step 2: Analyze the console.log statement

   The function logs the string plus the _id from the inserted document, so it outputs the actual _id value.

3. Final Answer:

   Document inserted with _id: [actual document _id] -> Option A

4. Quick Check:

   changeEvent.fullDocument._id logs inserted document ID [OK]

Hint: Insert triggers have fullDocument with new data [OK]

Common Mistakes:

• Assuming _id is undefined
• Thinking changeEvent is undefined
• Believing console.log doesn't work in triggers

4. You wrote this Atlas trigger function but it does not run as expected:

exports = function(changeEvent) {
  console.log('Change detected');
}

What is a likely reason it does not trigger?

medium

A. console.log is not allowed in triggers

B. The function syntax is invalid

C. The trigger is not linked to any database event

D. changeEvent parameter is missing

Solution

1. Step 1: Check function syntax and parameters

   The function syntax is correct and the changeEvent parameter is present, so no syntax error.

2. Step 2: Consider trigger configuration

   If the trigger is not linked to any database event or schedule, it will not run despite correct code.

3. Final Answer:

   The trigger is not linked to any database event -> Option C

4. Quick Check:

   Triggers must be linked to events to run [OK]

Hint: Check trigger event linkage if function doesn't run [OK]

Common Mistakes:

• Assuming console.log is disallowed
• Thinking syntax error causes no run
• Ignoring trigger event configuration

5. You want to create an Atlas trigger that runs every day at midnight to archive old documents. Which trigger type should you choose?

hard

A. Database trigger on insert event

B. Scheduled trigger with a cron expression

C. Database trigger on update event

D. Manual trigger run from the UI

Solution

1. Step 1: Identify trigger types for scheduled tasks

   Atlas supports scheduled triggers that run based on time using cron expressions.

2. Step 2: Match the requirement to trigger type

   To run daily at midnight, a scheduled trigger with a cron expression is the correct choice.

3. Final Answer:

   Scheduled trigger with a cron expression -> Option B

4. Quick Check:

   Scheduled triggers = run code on time schedule [OK]

Hint: Use scheduled triggers for time-based automation [OK]

Common Mistakes:

• Choosing database triggers for time schedules
• Thinking manual triggers run automatically
• Confusing insert/update triggers with scheduled