Transaction handling in GraphQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to start a transaction in GraphQL.

GraphQL

mutation StartTransaction {
  [1] {
    success
  }
}

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

AbeginTransaction

BcommitTransaction

CrollbackTransaction

DendTransaction

Attempts:

3 left

💡 Hint

Common Mistakes

Using commitTransaction to start instead of commit at the end.

Using rollbackTransaction which cancels changes.

The beginTransaction mutation starts a new transaction.

2fill in blank

medium

Complete the code to commit a transaction after changes.

GraphQL

mutation CommitChanges {
  [1] {
    success
  }
}

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

AcommitTransaction

BbeginTransaction

CrollbackTransaction

DsaveTransaction

Attempts:

3 left

💡 Hint

Common Mistakes

Using rollbackTransaction which cancels changes.

Using beginTransaction which starts but does not save.

The commitTransaction mutation saves all changes made during the transaction.

3fill in blank

hard

Fix the error in the mutation to cancel a transaction.

GraphQL

mutation CancelTransaction {
  [1] {
    success
  }
}

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

AcommitTransaction

BrollbackTransaction

CbeginTransaction

DcancelTransaction

Attempts:

3 left

💡 Hint

Common Mistakes

Using commitTransaction which saves changes.

Using beginTransaction which starts a transaction.

The rollbackTransaction mutation cancels all changes made during the transaction.

4fill in blank

hard

Fill both blanks to start and then commit a transaction.

GraphQL

mutation ManageTransaction {
  [1] {
    success
  }
  [2] {
    success
  }
}

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

AbeginTransaction

BcommitTransaction

CrollbackTransaction

DendTransaction

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping commit and rollback.

Using endTransaction which is not standard.

First, beginTransaction starts the transaction, then commitTransaction saves the changes.

5fill in blank

hard

Fill all three blanks to start, rollback, and then commit a transaction correctly.

GraphQL

mutation ComplexTransaction {
  [1] {
    success
  }
  [2] {
    success
  }
  [3] {
    success
  }
}

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

AbeginTransaction

BcommitTransaction

CrollbackTransaction

DendTransaction

Attempts:

3 left

💡 Hint

Common Mistakes

Committing before rollback.

Using endTransaction which is not standard.

Start with beginTransaction, then rollbackTransaction cancels changes, and finally commitTransaction saves if needed.

Practice

1. What is the main purpose of using transactions in a database when working with GraphQL?

easy

A. To group multiple actions so they all succeed or fail together

B. To speed up query execution by caching results

C. To automatically generate GraphQL schemas

D. To encrypt data sent over the network

Solution

1. Step 1: Understand what transactions do

   Transactions ensure that a set of database operations are treated as a single unit.

2. Step 2: Identify the purpose in GraphQL context

   This means either all changes succeed or none do, keeping data consistent.

3. Final Answer:

   To group multiple actions so they all succeed or fail together -> Option A

4. Quick Check:

   Transactions = atomic group actions [OK]

Hint: Transactions keep multiple changes safe together [OK]

Common Mistakes:

• Thinking transactions speed up queries
• Confusing transactions with schema generation
• Assuming transactions encrypt data

2. Which of the following is the correct way to start a transaction in a GraphQL resolver using a typical backend?

easy

A. const transaction = await db.rollback();

B. const transaction = db.commit();

C. const transaction = await db.startTransaction();

D. const transaction = db.query('BEGIN');

Solution

1. Step 1: Identify how to start a transaction

   Starting a transaction usually involves calling a method like startTransaction() asynchronously.

2. Step 2: Check options for correctness

   const transaction = await db.startTransaction(); correctly uses await and startTransaction(), while others are commit, rollback, or raw query.

3. Final Answer:

   const transaction = await db.startTransaction(); -> Option C

4. Quick Check:

   Start transaction = startTransaction() [OK]

Hint: Start transactions with async startTransaction() method [OK]

Common Mistakes:

• Using commit or rollback to start a transaction
• Using raw query strings instead of methods
• Missing await for async calls

3. Given this GraphQL resolver snippet, what will be the output if an error occurs during updateUser()?

async function updateProfile(parent, args, context) {
  const trx = await context.db.startTransaction();
  try {
    await trx.updateUser(args.userId, args.data);
    await trx.commit();
    return 'Success';
  } catch (e) {
    await trx.rollback();
    return 'Failed';
  }
}

medium

A. 'Success'

B. 'Failed'

C. Throws an unhandled exception

D. Returns null

Solution

1. Step 1: Analyze the try block

   The code tries to update the user and commit the transaction.

2. Step 2: Understand error handling

   If updateUser throws an error, the catch block rolls back and returns 'Failed'.

3. Final Answer:

   'Failed' -> Option B

4. Quick Check:

   Error during update = rollback + 'Failed' [OK]

Hint: Errors trigger rollback and return 'Failed' [OK]

Common Mistakes:

• Assuming commit runs even on error
• Expecting unhandled exceptions instead of catch
• Thinking it returns 'Success' always

4. Identify the error in this GraphQL resolver transaction handling code:

async function saveOrder(parent, args, context) {
  const trx = context.db.startTransaction();
  try {
    await trx.insertOrder(args.order);
    await trx.commit();
    return 'Order saved';
  } catch (error) {
    await trx.rollback();
    return 'Error saving order';
  }
}

medium

A. Missing await before startTransaction()

B. No rollback in catch block

C. commit() should be called before insertOrder()

D. Returning string instead of object

Solution

1. Step 1: Check transaction start syntax

   startTransaction() is asynchronous and must be awaited.

2. Step 2: Identify missing await impact

   Without await, trx is a Promise, causing errors on trx.insertOrder().

3. Final Answer:

   Missing await before startTransaction() -> Option A

4. Quick Check:

   Async startTransaction() needs await [OK]

Hint: Always await async transaction start calls [OK]

Common Mistakes:

• Forgetting await on async calls
• Calling commit before operations
• Ignoring rollback on errors

5. You want to update a user's profile and their related settings in one transaction using GraphQL. Which approach ensures both updates succeed or fail together?

async function updateUserAndSettings(parent, args, context) {
  const trx = await context.db.startTransaction();
  try {
    await trx.updateUser(args.userId, args.userData);
    await trx.updateSettings(args.userId, args.settingsData);
    await trx.commit();
    return 'Update successful';
  } catch (error) {
    await trx.rollback();
    return 'Update failed';
  }
}

hard

A. Use separate transactions for user and settings updates

B. Do not use transactions for related updates

C. Commit after each update separately

D. Wrap both updates in a single transaction as shown

Solution

1. Step 1: Understand transaction grouping

   Both updates must be inside one transaction to succeed or fail together.

2. Step 2: Analyze the code approach

   The code wraps both updates in one transaction, committing only if both succeed.

3. Final Answer:

   Wrap both updates in a single transaction as shown -> Option D

4. Quick Check:

   Single transaction = atomic multi-update [OK]

Hint: Group related updates in one transaction [OK]

Common Mistakes:

• Using separate transactions causing partial updates
• Committing too early after first update
• Skipping transactions for multi-step changes