Session and transaction syntax in MongoDB - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to start a client session in MongoDB.

MongoDB

const session = client.[1]();

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

AcreateSession

BbeginSession

CopenSession

DstartSession

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'beginSession' instead of 'startSession'.

Trying to call 'openSession' which does not exist.

In MongoDB, startSession() is the correct method to begin a client session.

2fill in blank

medium

Complete the code to start a transaction inside a session.

MongoDB

session.[1]();

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

AopenTransaction

BbeginTransaction

CstartTransaction

DinitTransaction

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'beginTransaction' which is not a valid method.

Trying 'openTransaction' which does not exist.

The correct method to start a transaction in a session is startTransaction().

3fill in blank

hard

Fix the error in the code to commit a transaction.

MongoDB

await session.[1]();

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

AendTransaction

BcommitTransaction

Ccommit

DfinalizeTransaction

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'commit' which is not a method on session.

Trying 'endTransaction' which does not exist.

The correct method to commit a transaction is commitTransaction().

4fill in blank

hard

Fill both blanks to abort a transaction and end the session.

MongoDB

await session.[1]();
session.[2]();

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

AabortTransaction

BendSession

CcloseSession

DrollbackTransaction

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'rollbackTransaction' which is not a MongoDB method.

Using 'closeSession' instead of 'endSession'.

To abort a transaction, use abortTransaction(). To end the session, use endSession().

5fill in blank

hard

Fill all three blanks to run a transaction with a callback function.

MongoDB

await session.withTransaction(async () => {
  await collection.[1](doc, { session: [2] });
}, { readPreference: [3] });

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

AinsertOne

Bsession

C'primary'

DupdateOne

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'updateOne' instead of 'insertOne' for adding a document.

Passing something other than 'session' as the session option.

Using a wrong read preference like 'secondary'.

Inside the transaction callback, use insertOne to add a document. Pass the session object to the operation. Set readPreference to 'primary' for strong consistency.

Practice

1. What is the main purpose of using startSession() in MongoDB?

easy

A. To commit changes to the database

B. To begin a session that groups operations for transactions

C. To abort a running transaction

D. To create a new database

Solution

1. Step 1: Understand the role of sessions

   Sessions in MongoDB group multiple operations so they can be executed as a single unit.

2. Step 2: Identify what startSession() does

   This method starts a new session to enable transactions or grouped operations.

3. Final Answer:

   To begin a session that groups operations for transactions -> Option B

4. Quick Check:

   startSession() starts a session [OK]

Hint: Sessions group operations; startSession() begins it [OK]

Common Mistakes:

• Confusing startSession() with commitTransaction()
• Thinking startSession() commits or aborts transactions
• Assuming startSession() creates a database

2. Which of the following is the correct syntax to start a transaction in a MongoDB session named session?

easy

A. session.beginTransaction()

B. session.transactionStart()

C. session.startTransaction()

D. session.openTransaction()

Solution

1. Step 1: Recall the MongoDB transaction method

   The correct method to start a transaction on a session object is startTransaction().

2. Step 2: Check each option's syntax

   Only session.startTransaction() matches the official MongoDB API.

3. Final Answer:

   session.startTransaction() -> Option C

4. Quick Check:

   startTransaction() starts transactions [OK]

Hint: Use startTransaction() to begin transactions on sessions [OK]

Common Mistakes:

• Using beginTransaction() which is not a MongoDB method
• Mixing method names like transactionStart()
• Using openTransaction() which does not exist

3. Given the following code snippet, what will be the output if the transaction commits successfully?

const session = client.startSession();
session.startTransaction();
await collection.insertOne({name: 'Alice'}, {session});
await session.commitTransaction();
session.endSession();
console.log('Transaction complete');

medium

A. No output

B. Transaction aborted

C. SyntaxError

D. Transaction complete

Solution

1. Step 1: Analyze the transaction flow

   The code starts a session, begins a transaction, inserts a document, commits the transaction, and ends the session.

2. Step 2: Determine the output after commit

   Since commitTransaction() is awaited and no errors occur, the console.log will print 'Transaction complete'.

3. Final Answer:

   Transaction complete -> Option D

4. Quick Check:

   Successful commit logs 'Transaction complete' [OK]

Hint: commitTransaction() success leads to 'Transaction complete' log [OK]

Common Mistakes:

• Assuming commitTransaction() throws error without cause
• Thinking session.endSession() prevents console.log
• Confusing commitTransaction() with abortTransaction()

4. Identify the error in the following MongoDB transaction code:

const session = client.startSession();
session.startTransaction();
await collection.insertOne({item: 'book'});
await session.commitTransaction();
session.endSession();

medium

A. Missing session option in insertOne operation

B. startSession() should be called after startTransaction()

C. commitTransaction() should be called before insertOne

D. endSession() should be called before commitTransaction()

Solution

1. Step 1: Review transaction usage in operations

   Operations inside a transaction must include the session option to be part of it.

2. Step 2: Check the insertOne call

   The insertOne call lacks the {session} option, so it is not part of the transaction.

3. Final Answer:

   Missing session option in insertOne operation -> Option A

4. Quick Check:

   Operations need {session} to join transaction [OK]

Hint: Include {session} in operations inside transactions [OK]

Common Mistakes:

• Calling startSession() after startTransaction()
• Calling commitTransaction() before operations
• Ending session before committing transaction

5. You want to ensure that either all writes in a batch succeed or none do in MongoDB. Which sequence of commands correctly implements this using sessions and transactions?

hard

A. const session = client.startSession(); session.startTransaction(); await collection.insertOne(doc1, {session}); await collection.insertOne(doc2, {session}); await session.commitTransaction(); session.endSession();

B. const session = client.startSession(); await collection.insertOne(doc1); await collection.insertOne(doc2); session.startTransaction(); await session.commitTransaction(); session.endSession();

C. const session = client.startSession(); session.startTransaction(); await collection.insertOne(doc1); await collection.insertOne(doc2); session.abortTransaction(); session.endSession();

D. const session = client.startSession(); await session.startTransaction(); await collection.insertOne(doc1, {session}); await collection.insertOne(doc2, {session}); await session.abortTransaction(); session.endSession();

Solution

1. Step 1: Understand transaction requirements

   All operations must be inside a started transaction and include the session option.

2. Step 2: Evaluate each option

   const session = client.startSession(); session.startTransaction(); await collection.insertOne(doc1, {session}); await collection.insertOne(doc2, {session}); await session.commitTransaction(); session.endSession(); correctly starts a session, starts a transaction, performs writes with session, commits, and ends session. Others either miss session in operations, start transaction late, or abort instead of commit.

3. Final Answer:

   const session = client.startSession(); session.startTransaction(); await collection.insertOne(doc1, {session}); await collection.insertOne(doc2, {session}); await session.commitTransaction(); session.endSession(); -> Option A

4. Quick Check:

   Start session, startTransaction, ops with session, commit, endSession [OK]

Hint: Start session, startTransaction, ops with session, commit, endSession [OK]

Common Mistakes:

• Not passing {session} in operations
• Starting transaction after operations
• Aborting instead of committing for success