PutItem (creating items) in DynamoDB - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What happens when you put an item with an existing primary key?

You have a DynamoDB table with a primary key id. You run a PutItem operation with an item that has the same id as an existing item but different attribute values. What will be the result?

DynamoDB

PutItem({TableName: 'Users', Item: {id: {S: '123'}, name: {S: 'Alice'}}})
PutItem({TableName: 'Users', Item: {id: {S: '123'}, name: {S: 'Bob'}}})

A The item with id '123' is replaced with the new item having name 'Bob'.

B The operation fails with a ConditionalCheckFailedException.

C The new item is added alongside the old item, so two items with id '123' exist.

D The operation is ignored and the old item remains unchanged.

💡 Hint

Think about how PutItem works with existing keys in DynamoDB.

PutItem replaces the entire item if the primary key already exists. It does not merge or add duplicates.

📝 Syntax

intermediate

Which PutItem request is syntactically correct?

Choose the correct DynamoDB PutItem request syntax to add an item with id as a string and age as a number.

A {TableName: 'People', Item: {id: '001', age: 30}}

B {TableName: 'People', Item: {id: S:'001', age: N:'30'}}

C {TableName: 'People', Item: {id: {S: '001'}, age: {N: '30'}}}

D {TableName: 'People', Item: {id: {String: '001'}, age: {Number: 30}}}

💡 Hint

Remember DynamoDB expects attribute values to be typed with S for string and N for number, both as strings.

Option C uses the correct attribute value format: {S: 'string'} and {N: 'number_as_string'}.

❓ optimization

advanced

How to avoid overwriting existing items when using PutItem?

You want to add a new item only if an item with the same primary key does not exist. Which option correctly achieves this using PutItem?

A Use <code>ConditionExpression: 'attribute_not_exists(id)'</code> in the PutItem request.

B Use <code>ReturnValues: 'ALL_OLD'</code> in the PutItem request.

C Use <code>UpdateItem</code> instead of <code>PutItem</code>.

D Use <code>PutItem</code> without any condition; it will not overwrite existing items.

💡 Hint

Think about how to tell DynamoDB to only put if the item does not exist.

The ConditionExpression with attribute_not_exists prevents overwriting by failing the operation if the key exists.

🔧 Debug

advanced

Why does this PutItem request fail with ValidationException?

Consider this PutItem request:

{
  TableName: 'Orders',
  Item: {
    orderId: {S: 'A123'},
    amount: {N: 100}
  }
}

Why does it fail with a ValidationException?

A The table name 'Orders' does not exist.

B The primary key attribute name is incorrect; it should be <code>id</code> not <code>orderId</code>.

C The attribute <code>amount</code> cannot be a number.

D The number value must be a string, so <code>{N: '100'}</code> is required instead of <code>{N: 100}</code>.

💡 Hint

Check the data types required by DynamoDB for number attributes.

DynamoDB requires number attributes to be strings representing numbers, so {N: '100'} is correct.

🧠 Conceptual

expert

What is the effect of using ReturnValues='ALL_OLD' in PutItem?

You perform a PutItem operation with ReturnValues set to 'ALL_OLD'. What will the response contain if the item already existed?

A The response contains the new item that was just inserted.

B The response contains the entire old item that was replaced by the new item.

C The response contains only the primary key of the old item.

D The response is empty regardless of whether the item existed.

💡 Hint

Think about what ReturnValues='ALL_OLD' means in DynamoDB PutItem.

When ReturnValues='ALL_OLD' is set, DynamoDB returns the entire item that was replaced if it existed before.