Atlas triggers overview in MongoDB - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a trigger that runs on document insert.

MongoDB

exports = function(changeEvent) { if (changeEvent.operationType === '[1]') { console.log("Document inserted"); } };

Drag options to blanks, or click blank then click option'

Areplace

Bupdate

Cdelete

Dinsert

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'update' or 'delete' instead of 'insert'.

The trigger listens for the insert operation type to run when a new document is added.

2fill in blank

medium

Complete the code to access the full document after an update in a trigger.

MongoDB

exports = function(changeEvent) { const fullDoc = changeEvent.[1]; console.log(fullDoc); };

Drag options to blanks, or click blank then click option'

AdocumentKey

BfullDocument

CupdateDescription

Dns

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'documentKey' which only has the document ID.

The fullDocument field contains the entire document after the update.

3fill in blank

hard

Fix the error in the trigger code to correctly check for a delete operation.

MongoDB

exports = function(changeEvent) { if (changeEvent.operationType === '[1]') { console.log("Document deleted"); } };

Drag options to blanks, or click blank then click option'

Adrop

Bremove

Cdelete

Ddestroy

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'remove' or 'drop' which are not valid operationType values.

The correct operationType for a delete event is delete.

4fill in blank

hard

Fill both blanks to filter trigger events only for updates on the 'status' field.

MongoDB

exports = function(changeEvent) { if (changeEvent.operationType === '[1]' && changeEvent.updateDescription.updatedFields.[2] !== undefined) { console.log("Status field updated"); } };

Drag options to blanks, or click blank then click option'

Aupdate

Binsert

Cstatus

Dname

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'insert' instead of 'update' or wrong field names.

The trigger checks for update operations and specifically if the status field was changed.

5fill in blank

hard

Fill all three blanks to log the document ID and new value of 'score' after an update.

MongoDB

exports = function(changeEvent) { const docId = changeEvent.[1]._id; const newScore = changeEvent.updateDescription.updatedFields.[2]; console.log(`Document ID: ${docId}, New Score: ${newScore}`); if (changeEvent.operationType === '[3]') { /* additional logic */ } };

Drag options to blanks, or click blank then click option'

AdocumentKey

Bscore

Cupdate

DfullDocument

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'fullDocument' for ID or wrong operationType.

The documentKey holds the document ID, score is the updated field, and the operationType is update.

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