Commit and abort behavior in MongoDB - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to start a transaction in MongoDB.

MongoDB

const session = client.startSession();
session.[1]();

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

AcommitTransaction

BendSession

CabortTransaction

DstartTransaction

Attempts:

3 left

💡 Hint

Common Mistakes

Using commitTransaction instead of startTransaction.

Calling endSession before starting a transaction.

To begin a transaction, you must call startTransaction() on the session.

2fill in blank

medium

Complete the code to commit a transaction in MongoDB.

MongoDB

await session.[1]();

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

AstartTransaction

BcommitTransaction

CabortTransaction

DendSession

Attempts:

3 left

💡 Hint

Common Mistakes

Using abortTransaction instead of commitTransaction.

Calling startTransaction again instead of committing.

To save all changes made in a transaction, use commitTransaction().

3fill in blank

hard

Fix the error in aborting a transaction in MongoDB.

MongoDB

await session.[1]();

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

AabortTransaction

BstartTransaction

CcommitTransaction

DendSession

Attempts:

3 left

💡 Hint

Common Mistakes

Using commitTransaction instead of abortTransaction.

Calling endSession instead of aborting.

To cancel all changes in a transaction, use abortTransaction().

4fill in blank

hard

Fill both blanks to correctly use a transaction with commit and session end.

MongoDB

try {
  await session.[1]();
  // perform operations
  await session.[2]();
} finally {
  await session.endSession();
}

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

AcommitTransaction

BstartTransaction

CabortTransaction

DendSession

Attempts:

3 left

💡 Hint

Common Mistakes

Committing before starting the transaction.

Using abortTransaction instead of commitTransaction.

Start the transaction with startTransaction() and commit it with commitTransaction().

5fill in blank

hard

Fill all three blanks to abort a transaction and end the session properly.

MongoDB

try {
  await session.[1]();
  // perform operations
  if (error) {
    await session.[2]();
  } else {
    await session.commitTransaction();
  }
} finally {
  await session.[3]();
}

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

AstartTransaction

BabortTransaction

CendSession

DcommitTransaction

Attempts:

3 left

💡 Hint

Common Mistakes

Not ending the session after aborting.

Using commitTransaction instead of abortTransaction on error.

Start the transaction, abort if error, and always end the session.

Practice

1. What happens when you commit a transaction in MongoDB?

easy

A. All changes made during the transaction are saved permanently.

B. All changes made during the transaction are discarded.

C. The transaction is paused and can be resumed later.

D. Only some changes are saved, others are lost.

Solution

1. Step 1: Understand commit behavior

   Committing a transaction means saving all changes made during that transaction permanently to the database.

2. Step 2: Compare with abort

   Unlike abort, which cancels changes, commit finalizes them.

3. Final Answer:

   All changes made during the transaction are saved permanently. -> Option A

4. Quick Check:

   Commit = Save changes [OK]

Hint: Commit means save all changes made in the transaction [OK]

Common Mistakes:

• Confusing commit with abort
• Thinking commit only saves some changes
• Believing commit pauses the transaction

2. Which of the following is the correct syntax to abort a transaction in MongoDB using the shell?

easy

A. transaction.abort()

B. session.abortTransaction()

C. db.abort()

D. session.commit()

Solution

1. Step 1: Recall MongoDB transaction abort syntax

   The correct method to abort a transaction is session.abortTransaction().

2. Step 2: Eliminate incorrect options

   session.commit() is invalid, db.abort() and transaction.abort() are not valid MongoDB shell commands.

3. Final Answer:

   session.abortTransaction() -> Option B

4. Quick Check:

   Abort transaction = session.abortTransaction() [OK]

Hint: Abort transaction uses session.abortTransaction() method [OK]

Common Mistakes:

• Using commit() instead of abortTransaction()
• Trying to abort with db.abort() which doesn't exist
• Confusing transaction object with session

3. Consider this MongoDB transaction code snippet:

const session = client.startSession();
session.startTransaction();
await collection.insertOne({name: 'Alice'}, {session});
await session.abortTransaction();
const count = await collection.countDocuments({name: 'Alice'});
console.log(count);

What will be printed?

medium

A. 0

B. 1

C. undefined

D. Error

Solution

1. Step 1: Analyze transaction operations

   The document insertion happens inside a transaction that is aborted immediately after.

2. Step 2: Understand abort effect on data

   Aborting the transaction cancels the insert, so the document is not saved.

3. Final Answer:

   0 -> Option A

4. Quick Check:

   Abort cancels insert, count = 0 [OK]

Hint: Aborted inserts do not persist, count remains zero [OK]

Common Mistakes:

• Assuming insert stays after abort
• Expecting count to be 1
• Thinking abort throws error

4. You wrote this MongoDB transaction code but it throws an error:

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

What is the likely cause of the error?

medium

A. insertOne() is missing session option

B. startTransaction() is called twice

C. Missing await before commitTransaction()

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

Solution

1. Step 1: Check async calls in transaction

   commitTransaction() returns a promise and must be awaited to complete properly.

2. Step 2: Identify missing await causes error

   Without await, the code may proceed before commit finishes, causing errors.

3. Final Answer:

   Missing await before commitTransaction() -> Option C

4. Quick Check:

   Async commit needs await [OK]

Hint: Always await commitTransaction() to avoid errors [OK]

Common Mistakes:

• Not awaiting commitTransaction()
• Calling startTransaction() multiple times
• Calling endSession() too early

5. You want to update two documents atomically in MongoDB. You start a transaction, update the first document, then update the second. If the second update fails, what should you do to ensure no partial changes remain?

hard

A. Manually delete the first update after failure.

B. Commit the transaction to save the first update only.

C. Ignore the failure and continue.

D. Abort the transaction to cancel all changes.

Solution

1. Step 1: Understand atomicity in transactions

   Transactions ensure all-or-nothing changes. If one update fails, the whole transaction should be canceled.

2. Step 2: Apply abort to cancel partial changes

   Aborting the transaction cancels all changes, preventing partial updates.

3. Final Answer:

   Abort the transaction to cancel all changes. -> Option D

4. Quick Check:

   Fail in transaction = abort all changes [OK]

Hint: Abort transaction to avoid partial updates on failure [OK]

Common Mistakes:

• Committing partial updates
• Trying to manually fix partial changes
• Ignoring failure and continuing