Transaction conditions in DynamoDB - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to add a condition that the attribute 'status' must equal 'active' in a DynamoDB transaction.

DynamoDB

TransactItems: [{ Update: { Key: { id: '123' }, UpdateExpression: 'SET #s = :new', ConditionExpression: '#s = [1]', ExpressionAttributeNames: { '#s': 'status' }, ExpressionAttributeValues: { ':new': 'inactive', ':active': 'active' } } }]

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

A'inactive'

B'pending'

C'active'

D'deleted'

Attempts:

3 left

💡 Hint

Common Mistakes

Using the new value 'inactive' instead of the current expected value 'active'.

Forgetting to put quotes around the string value.

The condition expression requires the 'status' attribute to be 'active' before updating. So, the correct value is 'active'.

2fill in blank

medium

Complete the code to ensure the transaction only proceeds if the attribute 'count' is less than 10.

DynamoDB

TransactItems: [{ Put: { Item: { id: '456', count: 1 }, ConditionExpression: 'attribute_exists(id) AND [1] < :max', ExpressionAttributeValues: { ':max': 10 } } }]

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

Avalue

Bid

Cstatus

Dcount

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'id' or other unrelated attributes in the condition.

Omitting the attribute name in the condition expression.

The condition checks that 'count' is less than 10 before putting the item. So 'count' is the correct attribute.

3fill in blank

hard

Fix the error in the condition expression to check that attribute 'version' equals 3 before updating.

DynamoDB

TransactItems: [{ Update: { Key: { id: '789' }, UpdateExpression: 'SET version = version + 1', ConditionExpression: 'version = [1]' } }]

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

A3

B'3'

C:3

D#3

Attempts:

3 left

💡 Hint

Common Mistakes

Using quotes around the number, which makes it a string.

Using placeholders incorrectly like ':3' or '#3'.

The condition expression compares the attribute 'version' to the number 3, so the value should be the number 3 without quotes or symbols.

4fill in blank

hard

Fill both blanks to create a condition that attribute 'score' is greater than 50 and attribute 'level' is less than 10.

DynamoDB

ConditionExpression: '#sc [1] :minScore AND #lv [2] :maxLevel', ExpressionAttributeNames: { '#sc': 'score', '#lv': 'level' }, ExpressionAttributeValues: { ':minScore': 50, ':maxLevel': 10 }

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

A>

B<

C=

D>=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '=' instead of comparison operators.

Swapping the operators for the two attributes.

The condition requires 'score' to be greater than 50 and 'level' to be less than 10, so the operators are '>' and '<'.

5fill in blank

hard

Fill all three blanks to build a transaction condition that attribute 'status' equals 'pending', attribute 'attempts' is less than 5, and attribute 'priority' is greater than or equal to 1.

DynamoDB

ConditionExpression: '#st = [1] AND #at [2] :maxAttempts AND #pr [3] :minPriority', ExpressionAttributeNames: { '#st': 'status', '#at': 'attempts', '#pr': 'priority' }, ExpressionAttributeValues: { ':maxAttempts': 5, ':minPriority': 1 }

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

A'pending'

B<

C>=

D=

Attempts:

3 left

💡 Hint

Common Mistakes

Not using quotes around 'pending'.

Using wrong comparison operators like '=' instead of '<' or '>='.

The condition requires 'status' to be 'pending' (string with quotes), 'attempts' less than 5, and 'priority' greater than or equal to 1.

Practice

1. What is the main purpose of using ConditionCheck in a DynamoDB transaction?

easy

A. To ensure certain conditions are met before making changes to data

B. To speed up the transaction by skipping checks

C. To delete all items in a table

D. To create a backup of the database

Solution

1. Step 1: Understand ConditionCheck role

   ConditionCheck verifies if specified conditions are true before allowing a transaction to proceed.

2. Step 2: Recognize transaction safety

   If conditions fail, the transaction is aborted, preventing unwanted data changes.

3. Final Answer:

   To ensure certain conditions are met before making changes to data -> Option A

4. Quick Check:

   Transaction conditions = safety check [OK]

Hint: ConditionCheck = verify before change [OK]

Common Mistakes:

• Thinking ConditionCheck speeds up transactions
• Confusing ConditionCheck with data deletion
• Assuming ConditionCheck creates backups

2. Which of the following is the correct syntax snippet for a ConditionCheck in a DynamoDB transaction?

easy

A. "ConditionCheck": {"Key": {"Id": {"N": 123}}, "TableName": "MyTable", "ConditionExpression": "attribute_exists(Id)"}

B. "ConditionCheck": {"Key": {"Id": "123"}, "TableName": "MyTable", "ConditionExpression": "attribute_exists(Id)"}

C. "ConditionCheck": {"Key": {"Id": {"S": "123"}}, "TableName": "MyTable", "ConditionExpression": "attribute_exists(Id)"}

D. "ConditionCheck": {"Key": {"Id": {"S": 123}}, "TableName": "MyTable", "ConditionExpression": "attribute_exists(Id)"}

Solution

1. Step 1: Check key format for string type

   DynamoDB expects string values to be wrapped as {"S": "value"} in JSON.

2. Step 2: Validate ConditionExpression and TableName

   ConditionExpression uses attribute_exists correctly; TableName is properly specified.

3. Final Answer:

   "ConditionCheck": {"Key": {"Id": {"S": "123"}}, "TableName": "MyTable", "ConditionExpression": "attribute_exists(Id)"} -> Option C

4. Quick Check:

   Correct JSON key format = "ConditionCheck": {"Key": {"Id": {"S": "123"}}, "TableName": "MyTable", "ConditionExpression": "attribute_exists(Id)"} [OK]

Hint: Use {"S": "string"} for string keys in ConditionCheck [OK]

Common Mistakes:

• Omitting the type wrapper like {"S": ...}
• Using number type for string keys
• Passing raw values without quotes

3. Given this transaction snippet, what happens if the item with Id = '101' does not exist?

{
  "TransactItems": [
    {
      "ConditionCheck": {
        "TableName": "Orders",
        "Key": {"Id": {"S": "101"}},
        "ConditionExpression": "attribute_exists(Id)"
      }
    },
    {
      "Update": {
        "TableName": "Orders",
        "Key": {"Id": {"S": "101"}},
        "UpdateExpression": "SET Status = :s",
        "ExpressionAttributeValues": {":s": {"S": "Processed"}}
      }
    }
  ]
}

medium

A. The update runs anyway, creating a new item

B. The transaction partially updates the item

C. The transaction ignores the ConditionCheck and updates

D. The transaction fails and no update happens

Solution

1. Step 1: Understand ConditionCheck with attribute_exists

   The ConditionCheck requires the item with Id '101' to exist for the transaction to proceed.

2. Step 2: Analyze transaction behavior on condition failure

   If the item does not exist, the condition fails, so the entire transaction is aborted and no update occurs.

3. Final Answer:

   The transaction fails and no update happens -> Option D

4. Quick Check:

   Condition failure aborts transaction = The transaction fails and no update happens [OK]

Hint: ConditionCheck failure stops whole transaction [OK]

Common Mistakes:

• Assuming update creates new item on failure
• Thinking transaction partially applies changes
• Ignoring ConditionCheck effect

4. You wrote this transaction but it always fails with a validation error:

{
  "TransactItems": [
    {
      "ConditionCheck": {
        "TableName": "Users",
        "Key": {"UserId": {"N": "abc"}},
        "ConditionExpression": "attribute_exists(UserId)"
      }
    }
  ]
}

What is the most likely cause?

medium

A. ConditionExpression syntax is wrong

B. The key type is incorrect; 'abc' is not a number

C. TableName is misspelled

D. ConditionCheck cannot be used alone

Solution

1. Step 1: Check key type and value

   The key uses type "N" (number) but the value "abc" is not numeric, causing validation error.

2. Step 2: Confirm other parts are correct

   ConditionExpression and TableName syntax are valid; ConditionCheck can be used alone.

3. Final Answer:

   The key type is incorrect; 'abc' is not a number -> Option B

4. Quick Check:

   Key type must match value format [OK]

Hint: Match key type with value format [OK]

Common Mistakes:

• Using non-numeric string with number type
• Assuming ConditionExpression syntax error
• Thinking ConditionCheck needs other actions

5. You want to update a user's email only if their current email is exactly '[e-mail]'. Which transaction condition setup achieves this safely?

hard

A. Use a ConditionCheck with ConditionExpression 'Email = :oldEmail' before the update

B. Use an Update with ConditionExpression 'attribute_exists(Email)'

C. Use a ConditionCheck with ConditionExpression 'attribute_not_exists(Email)'

D. Update without any condition; trust the data is correct

Solution

1. Step 1: Identify condition to match exact current email

   The condition must check that Email equals '[e-mail]' before updating.

2. Step 2: Use ConditionCheck to verify before update

   ConditionCheck with 'Email = :oldEmail' ensures update only happens if current email matches.

3. Final Answer:

   Use a ConditionCheck with ConditionExpression 'Email = :oldEmail' before the update -> Option A

4. Quick Check:

   Exact match condition before update = Use a ConditionCheck with ConditionExpression 'Email = :oldEmail' before the update [OK]

Hint: Check exact value with ConditionCheck before update [OK]

Common Mistakes:

• Using attribute_exists instead of exact match
• Checking attribute_not_exists which is opposite
• Skipping condition and risking wrong update