Batch operations in Blockchain / Solidity - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a batch of transactions using the correct method.

Blockchain / Solidity

const batch = new web3.[1]();

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

ABatchOperations

BBatchRequest

CBatchTransactions

DTransactionBatch

Attempts:

3 left

💡 Hint

Common Mistakes

Using a non-existent class like TransactionBatch.

Confusing batch operations with single transactions.

The BatchRequest class is used to create a batch of requests in web3.js.

2fill in blank

medium

Complete the code to add a transaction call to the batch.

Blockchain / Solidity

batch.[1](contract.methods.transfer(toAddress, amount), callback);

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

Aadd

Bsend

Cqueue

Dpush

Attempts:

3 left

💡 Hint

Common Mistakes

Using send which executes immediately instead of adding to batch.

Using push which is not a method of batch.

The add method is used to add a request to the batch.

3fill in blank

hard

Fix the error in the code to execute the batch of transactions.

Blockchain / Solidity

batch.[1]();

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

Arun

Bprocess

Csend

Dexecute

Attempts:

3 left

💡 Hint

Common Mistakes

Using send which is for single transactions.

Using run or process which do not exist.

The execute method runs all requests in the batch.

4fill in blank

hard

Fill both blanks to create a batch and add a call to get the balance.

Blockchain / Solidity

const batch = new web3.[1]();
batch.[2](contract.methods.balanceOf(userAddress), callback);

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

ABatchRequest

Bsend

Cadd

Dexecute

Attempts:

3 left

💡 Hint

Common Mistakes

Using send instead of add to add calls.

Confusing batch creation with execution.

First, create a BatchRequest object, then add the balanceOf call to the batch.

5fill in blank

hard

Fill all three blanks to create a batch, add two calls, and execute the batch.

Blockchain / Solidity

const batch = new web3.[1]();
batch.[2](contract.methods.approve(spender, amount), callback);
batch.[3](contract.methods.allowance(owner, spender), callback);
batch.execute();

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

ABatchRequest

Badd

Csend

Dexecute

Attempts:

3 left

💡 Hint

Common Mistakes

Using send instead of add to add calls.

Trying to execute the batch before adding calls.

Create a BatchRequest, then add each call to the batch before executing.

Practice

1. What is the main benefit of using batch operations in blockchain?

easy

A. They allow only one task to run at a time for better security.

B. They increase the number of transactions to speed up the network.

C. They combine multiple tasks into one transaction to save time and fees.

D. They automatically fix errors in blockchain code.

Solution

1. Step 1: Understand batch operations purpose

   Batch operations group many tasks into a single transaction.

2. Step 2: Identify benefits

   This grouping saves time and reduces transaction fees by doing many tasks at once.

3. Final Answer:

   They combine multiple tasks into one transaction to save time and fees. -> Option C

4. Quick Check:

   Batch operations = save time and fees [OK]

Hint: Batch means many tasks in one go to save fees [OK]

Common Mistakes:

• Thinking batch operations increase transactions
• Believing batch operations run tasks one by one
• Assuming batch operations fix code errors automatically

2. Which of the following is the correct syntax to start a batch operation in a blockchain smart contract (pseudocode)?

easy

A. batch { /* tasks */ }

B. start batch { /* tasks */ }

C. beginBatch() /* tasks */ endBatch()

D. batch.start() { /* tasks */ }

Solution

1. Step 1: Recognize common batch syntax

   Batch operations often use a block or function named batch enclosing tasks.

2. Step 2: Compare options

   batch { /* tasks */ } uses batch { /* tasks */ } which is a common and clean way to group tasks.

3. Final Answer:

   batch { /* tasks */ } -> Option A

4. Quick Check:

   Batch block syntax = batch { } [OK]

Hint: Batch usually wraps tasks inside curly braces [OK]

Common Mistakes:

• Using incorrect keywords like start or beginBatch
• Missing curly braces for grouping tasks
• Confusing batch syntax with function calls

3. Given the following pseudocode for a batch operation:

batch {
  transfer(from: A, to: B, amount: 10)
  transfer(from: B, to: C, amount: 5)
  transfer(from: C, to: A, amount: 3)
}

What happens if the second transfer fails due to insufficient funds?

medium

A. All transfers are rolled back; none are applied.

B. Only the second transfer fails; the others succeed.

C. The batch skips the failed transfer and continues.

D. The batch completes but logs an error for the second transfer.

Solution

1. Step 1: Understand atomicity of batch operations

   Batch operations run all tasks together or none at all to keep data consistent.

2. Step 2: Apply failure effect

   If one task fails (second transfer), the entire batch is rolled back, so no transfers happen.

3. Final Answer:

   All transfers are rolled back; none are applied. -> Option A

4. Quick Check:

   Batch atomicity = all or nothing [OK]

Hint: If one fails, batch rolls back all tasks [OK]

Common Mistakes:

• Thinking partial batch tasks succeed
• Assuming batch skips failed tasks
• Believing batch logs errors but applies others

4. Consider this batch operation pseudocode:

batch {
  mintTokens(user: X, amount: 100)
  burnTokens(user: X, amount: 50)
  transferTokens(from: X, to: Y, amount: 60)
}

The batch fails with an error. What is the most likely cause?

medium

A. Minting tokens always fails in batch operations.

B. Trying to transfer more tokens than user X has after burning.

C. Burning tokens cannot be done inside a batch.

D. Batch operations do not support token transfers.

Solution

1. Step 1: Calculate user X's token balance after mint and burn

   User X mints 100 tokens, then burns 50, so balance is 50 tokens.

2. Step 2: Check transfer amount validity

   Transfer tries to send 60 tokens, which is more than 50 available, causing failure.

3. Final Answer:

   Trying to transfer more tokens than user X has after burning. -> Option B

4. Quick Check:

   Transfer > balance causes batch failure [OK]

Hint: Check token balances after each batch step [OK]

Common Mistakes:

• Assuming minting always fails
• Believing burning is not allowed in batch
• Thinking batch disallows transfers

5. You want to update multiple user balances atomically in a blockchain. Which approach best uses batch operations to ensure either all updates succeed or none do?

function updateBalances(updates) {
  batch {
    for (update in updates) {
      setBalance(user: update.user, amount: update.amount)
    }
  }
}

What is a key consideration to avoid silent failures in this batch?

hard

A. Use multiple batches for each user update.

B. Run each update outside batch to isolate errors.

C. Ignore errors inside batch to continue all updates.

D. Validate each update's amount before batch to prevent invalid data.

Solution

1. Step 1: Understand batch atomicity and error handling

   Batch runs all updates together; if one fails, all rollback. Silent failures can happen if invalid data is inside batch.

2. Step 2: Importance of pre-validation

   Validating each update before batch ensures no invalid data causes failure, avoiding silent rollback.

3. Final Answer:

   Validate each update's amount before batch to prevent invalid data. -> Option D

4. Quick Check:

   Pre-validate data to avoid batch rollback [OK]

Hint: Check data before batch to prevent rollback [OK]

Common Mistakes:

• Running updates outside batch loses atomicity
• Ignoring errors causes silent rollback
• Splitting updates into many batches loses efficiency