PutItem (creating items) in DynamoDB - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the PutItem operation do in DynamoDB?

PutItem adds a new item or replaces an old item with a new one in a DynamoDB table.

beginner

Which key attribute must you always include when using PutItem?

You must include the primary key attribute(s) defined for the table, such as the partition key and optionally the sort key.

intermediate

What happens if you use PutItem with an item that has the same primary key as an existing item?

The existing item is completely replaced by the new item you provide.

intermediate

How can you prevent overwriting an existing item when using PutItem?

Use a condition expression to check that the item does not already exist before inserting.

beginner

Give an example of a simple PutItem request in DynamoDB.

Example: {"TableName": "Users", "Item": {"UserId": {"S": "123"}, "Name": {"S": "Alice"}}}

What does PutItem do if the item key already exists in the table?

A It replaces the entire existing item with the new item.

B It deletes the old item and inserts the new one.

C It updates only the specified attributes.

D It returns an error and does nothing.

PutItem replaces the entire existing item with the new item if the primary key matches.

Which attribute is mandatory in the Item you provide to PutItem?

A The primary key attribute(s) of the table.

B Any attribute you want to add.

C A timestamp attribute.

D A condition expression.

The primary key attribute(s) must be included to uniquely identify the item.

How can you avoid overwriting an existing item when using PutItem?

A Delete the item first.

B Use UpdateItem instead.

C Use a condition expression to check item existence.

D PutItem always overwrites; you cannot avoid it.

A condition expression can prevent PutItem from overwriting if the item already exists.

What is the minimum required parameter for a PutItem request?

A TableName only.

B TableName and Item.

C Item only.

D ConditionExpression.

You must specify the table name and the item to insert.

If you want to add a new user with ID '101' and name 'Bob', which is a valid PutItem Item format?

A {"UserId": {"N": "101"}, "Name": {"S": "Bob"}}

B {"UserId": "101", "Name": "Bob"}

C {"UserId": 101, "Name": "Bob"}

D {"UserId": {"S": "101"}, "Name": {"S": "Bob"}}

DynamoDB expects attribute values with types, e.g., {"S": "string"} for strings.

Explain how PutItem works in DynamoDB and what happens if the item key already exists.

Think about inserting and overwriting items.

Describe how to prevent overwriting an existing item when using PutItem.

Conditions can control when PutItem succeeds.

Practice

1. What does the PutItem operation do in DynamoDB?

easy

A. Reads an item from a table

B. Deletes an item from a table

C. Updates only specific attributes of an item

D. Adds a new item or replaces an existing item in a table

Solution

1. Step 1: Understand the purpose of PutItem

   PutItem is used to add a new item or replace an existing item in a DynamoDB table.

2. Step 2: Compare with other operations

   Delete removes items, Get reads items, and Update modifies specific attributes, so they differ from PutItem.

3. Final Answer:

   Adds a new item or replaces an existing item in a table -> Option D

4. Quick Check:

   PutItem = Add or replace item [OK]

Hint: PutItem adds or replaces whole items, not partial updates [OK]

Common Mistakes:

• Confusing PutItem with UpdateItem
• Thinking PutItem only adds without replacing
• Mixing PutItem with Delete or Get operations

2. Which of the following is the correct syntax snippet to add an item with PutItem in DynamoDB using AWS SDK?

easy

A. dynamodb.putItem({ TableName: 'Users', Item: { 'UserId': { S: '123' }, 'Name': { S: 'Alice' } } })

B. dynamodb.put({ Table: 'Users', Item: { UserId: '123', Name: 'Alice' } })

C. dynamodb.insertItem({ TableName: 'Users', Item: { 'UserId': '123', 'Name': 'Alice' } })

D. dynamodb.addItem({ TableName: 'Users', Item: { 'UserId': { N: 123 }, 'Name': { S: 'Alice' } } })

Solution

1. Step 1: Check the correct method and parameters

   The AWS SDK method is putItem with parameters TableName and Item where each attribute has a type like S for string.

2. Step 2: Validate the attribute format

   dynamodb.putItem({ TableName: 'Users', Item: { 'UserId': { S: '123' }, 'Name': { S: 'Alice' } } }) uses the correct method and attribute typing. Other options use wrong method names or omit types.

3. Final Answer:

   dynamodb.putItem({ TableName: 'Users', Item: { 'UserId': { S: '123' }, 'Name': { S: 'Alice' } } }) -> Option A

4. Quick Check:

   Correct method and typed attributes = dynamodb.putItem({ TableName: 'Users', Item: { 'UserId': { S: '123' }, 'Name': { S: 'Alice' } } }) [OK]

Hint: Use putItem with typed attributes like { S: 'value' } [OK]

Common Mistakes:

• Using wrong method names like put or insertItem
• Not specifying attribute types (S, N, etc.)
• Using wrong parameter names like Table instead of TableName

3. Given the following PutItem request, what will be the result in the DynamoDB table?

{
  TableName: 'Products',
  Item: {
    'ProductId': { S: 'p100' },
    'Name': { S: 'Pen' },
    'Price': { N: '5' }
  }
}

medium

A. An error occurs because Price is a number but given as a string

B. Only the ProductId attribute is saved, others are ignored

C. A new item with ProductId 'p100', Name 'Pen', and Price 5 is added or replaced

D. The item is added but Price is stored as a string, not number

Solution

1. Step 1: Understand attribute types in PutItem

   In DynamoDB, number attributes are passed as strings inside the N type, so '5' is valid for number.

2. Step 2: Result of PutItem operation

   The item with all specified attributes is added or replaces existing item with same ProductId.

3. Final Answer:

   A new item with ProductId 'p100', Name 'Pen', and Price 5 is added or replaced -> Option C

4. Quick Check:

   PutItem stores typed attributes correctly = A new item with ProductId 'p100', Name 'Pen', and Price 5 is added or replaced [OK]

Hint: Number values are strings inside N type in PutItem [OK]

Common Mistakes:

• Thinking number values must be numeric type, not string
• Assuming partial attributes are saved
• Confusing attribute types and values

4. You try to run this PutItem request but get an error:

{
  TableName: 'Orders',
  Item: {
    'OrderId': 'o123',
    'Amount': { N: '100' }
  }
}

What is the likely cause of the error?

medium

A. The table name 'Orders' is invalid

B. The attribute 'OrderId' is missing its type wrapper like { S: 'o123' }

C. The number value '100' should be a number, not a string

D. The Item object must be an array, not an object

Solution

1. Step 1: Check attribute format in Item

   Each attribute must specify its type, e.g., { S: 'value' } for strings. Here, 'OrderId' lacks the type wrapper.

2. Step 2: Validate other parts

   TableName is valid, number values are strings inside N, and Item is an object, so those are correct.

3. Final Answer:

   The attribute 'OrderId' is missing its type wrapper like { S: 'o123' } -> Option B

4. Quick Check:

   All attributes need type wrappers = The attribute 'OrderId' is missing its type wrapper like { S: 'o123' } [OK]

Hint: Always wrap attributes with type like { S: 'text' } or { N: '123' } [OK]

Common Mistakes:

• Omitting type wrappers for string attributes
• Confusing number values as numeric instead of string
• Assuming Item can be an array

5. You want to add a new user item with UserId as the primary key and optional Age attribute only if it is provided (not null). Which PutItem approach correctly handles this conditional attribute?

hard

A. Include Age in the Item only if it is not null, otherwise omit it

B. Always include Age with value { N: '0' } if null

C. Set Age to an empty string { S: '' } when null

D. Use PutItem with a condition expression to skip Age attribute

Solution

1. Step 1: Understand optional attribute handling

   In DynamoDB PutItem, you include only attributes you want saved. Omitting optional attributes if null is correct.

2. Step 2: Evaluate other options

   Setting Age to zero or empty string changes data meaning. Condition expressions control item existence, not attribute presence.

3. Final Answer:

   Include Age in the Item only if it is not null, otherwise omit it -> Option A

4. Quick Check:

   Omit null attributes to avoid wrong data = Include Age in the Item only if it is not null, otherwise omit it [OK]

Hint: Only add attributes if they have real values, omit nulls [OK]

Common Mistakes:

• Adding attributes with zero or empty string instead of omitting
• Misusing condition expressions for attribute presence
• Assuming PutItem auto-skips null attributes