BatchGetItem in DynamoDB - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to specify the table name in the BatchGetItem request.

DynamoDB

{
  "RequestItems": {
    "[1]": {
      "Keys": [
        { "UserId": { "S": "123" } },
        { "UserId": { "S": "456" } }
      ]
    }
  }
}

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

AProducts

BOrders

CUsers

DInventory

Attempts:

3 left

💡 Hint

Common Mistakes

Using a wrong table name that does not exist.

Forgetting to put the table name as a key.

The table name must be specified as the key in the RequestItems object. Here, "Users" is the correct table name.

2fill in blank

medium

Complete the code to specify the key attribute name for the BatchGetItem request.

DynamoDB

{
  "RequestItems": {
    "Users": {
      "Keys": [
        { "[1]": { "S": "123" } },
        { "UserId": { "S": "456" } }
      ]
    }
  }
}

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

AOrderId

BUserId

CProductId

DInventoryId

Attempts:

3 left

💡 Hint

Common Mistakes

Using a key attribute name that does not exist in the table.

Mixing key names from different tables.

The key attribute name must match the primary key of the table. Here, "UserId" is the correct key for the Users table.

3fill in blank

hard

Fix the error in the BatchGetItem request by completing the missing attribute type.

DynamoDB

{
  "RequestItems": {
    "Users": {
      "Keys": [
        { "UserId": { "[1]": "123" } },
        { "UserId": { "S": "456" } }
      ]
    }
  }
}

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

AB

BN

CBOOL

DS

Attempts:

3 left

💡 Hint

Common Mistakes

Using N for string values causes errors.

Omitting the attribute type entirely.

The attribute type for a string value in DynamoDB is "S". This must be used to specify string keys.

4fill in blank

hard

Fill both blanks to specify the ProjectionExpression and ConsistentRead options in BatchGetItem.

DynamoDB

{
  "RequestItems": {
    "Users": {
      "Keys": [
        { "UserId": { "S": "123" } }
      ],
      "[1]": "UserName, Email",
      "[2]": true
    }
  }
}

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

AProjectionExpression

BConsistentRead

CFilterExpression

DReturnConsumedCapacity

Attempts:

3 left

💡 Hint

Common Mistakes

Using FilterExpression instead of ProjectionExpression.

Setting ConsistentRead to a string instead of boolean.

ProjectionExpression specifies which attributes to return. ConsistentRead set to true ensures strongly consistent reads.

5fill in blank

hard

Fill all three blanks to complete the BatchGetItem request with multiple tables and keys.

DynamoDB

{
  "RequestItems": {
    "Users": {
      "Keys": [
        { "UserId": { "S": "123" } },
        { "UserId": { "S": "456" } }
      ]
    },
    "[1]": {
      "Keys": [
        { "[2]": { "S": "789" } },
        { "OrderId": { "S": "101" } }
      ],
      "[3]": false
    }
  }
}

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

AOrders

BOrderId

CConsistentRead

DUsers

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong table name for the second table.

Mixing key attribute names between tables.

Setting ConsistentRead to a string instead of boolean.

The second table is "Orders". Its key attribute is "OrderId". The ConsistentRead option is set to false for eventually consistent reads.

Practice

1. What is the main purpose of the BatchGetItem operation in DynamoDB?

easy

A. To update multiple items in a table at once.

B. To retrieve multiple items from one or more tables using their primary keys in a single request.

C. To delete multiple items from a table in one call.

D. To scan the entire table and return all items.

Solution

1. Step 1: Understand BatchGetItem functionality

   BatchGetItem is designed to fetch multiple items quickly by specifying their primary keys.

2. Step 2: Compare with other operations

   Unlike update or delete, BatchGetItem only retrieves data, not modifies it.

3. Final Answer:

   To retrieve multiple items from one or more tables using their primary keys in a single request. -> Option B

4. Quick Check:

   BatchGetItem = fetch multiple items [OK]

Hint: BatchGetItem fetches multiple items by keys in one call [OK]

Common Mistakes:

• Confusing BatchGetItem with update or delete operations
• Thinking it scans the whole table
• Assuming it modifies data

2. Which of the following is the correct syntax snippet to specify keys in a BatchGetItem request in DynamoDB?

easy

A. "RequestItems": { "TableName": { "FilterExpression": "Id = :id" } }

B. "RequestItems": { "TableName": { "AttributesToGet": ["Id"] } }

C. "RequestItems": { "TableName": { "Keys": [{ "Id": { "S": "123" } }] } }

D. "RequestItems": { "TableName": { "UpdateExpression": "SET Name = :name" } }

Solution

1. Step 1: Identify BatchGetItem key specification

   BatchGetItem requires a "Keys" array with primary key objects for each item to fetch.

2. Step 2: Check each option

   "RequestItems": { "TableName": { "Keys": [{ "Id": { "S": "123" } }] } } correctly uses "Keys" with primary key format. Snippets using "AttributesToGet", "FilterExpression", or "UpdateExpression" are not valid for BatchGetItem keys.

3. Final Answer:

   "RequestItems": { "TableName": { "Keys": [{ "Id": { "S": "123" } }] } } -> Option C

4. Quick Check:

   Keys array = correct syntax [OK]

Hint: BatchGetItem keys go inside "Keys" array per table [OK]

Common Mistakes:

• Using FilterExpression instead of Keys
• Confusing AttributesToGet with Keys
• Trying to use UpdateExpression in BatchGetItem

3. Given the following BatchGetItem request, what will be the output if the table contains items with Ids 101 and 102 only?

{
  "RequestItems": {
    "Products": {
      "Keys": [
        { "Id": { "N": "101" } },
        { "Id": { "N": "103" } }
      ]
    }
  }
}

medium

A. Returns only item with Id 101

B. Returns all items in the Products table

C. Returns no items because 103 does not exist

D. Returns items with Id 101 and 103

Solution

1. Step 1: Understand BatchGetItem behavior with missing keys

   BatchGetItem returns only items that exist for the specified keys. Missing keys are ignored.

2. Step 2: Analyze given keys

   Id 101 exists, so it will be returned. Id 103 does not exist, so it will be skipped.

3. Final Answer:

   Returns only item with Id 101 -> Option A

4. Quick Check:

   Only existing keys returned [OK]

Hint: BatchGetItem skips missing keys, returns existing only [OK]

Common Mistakes:

• Expecting error if key not found
• Assuming all keys must exist
• Thinking it returns all table items

4. You wrote this BatchGetItem request but it returns a syntax error:

{
  "RequestItems": {
    "Orders": {
      "Keys": {
        "OrderId": { "S": "A123" }
      }
    }
  }
}

What is the error and how to fix it?

medium

A. RequestItems key name is misspelled.

B. OrderId should be a number, not a string.

C. BatchGetItem does not support multiple tables.

D. Keys must be an array of key objects, not a single object.

Solution

1. Step 1: Identify the Keys format error

   Keys must be an array of objects, but here it is a single object, causing syntax error.

2. Step 2: Correct the Keys format

   Wrap the key object inside an array: "Keys": [{ "OrderId": { "S": "A123" } }]

3. Final Answer:

   Keys must be an array of key objects, not a single object. -> Option D

4. Quick Check:

   Keys = array of key objects [OK]

Hint: Keys must always be an array, even for one item [OK]

Common Mistakes:

• Using object instead of array for Keys
• Wrong data type for key attribute
• Misspelling RequestItems

5. You want to fetch items from two tables, "Users" and "Orders", using BatchGetItem. You have 3 user IDs and 2 order IDs. Which of the following request structures correctly fetches all these items in one call?

hard

A. { "RequestItems": { "Users": { "Keys": [ { "UserId": { "S": "U1" } }, { "UserId": { "S": "U2" } }, { "UserId": { "S": "U3" } } ] }, "Orders": { "Keys": [ { "OrderId": { "S": "O1" } }, { "OrderId": { "S": "O2" } } ] } } }

B. { "RequestItems": { "Users": { "Keys": { "UserId": ["U1", "U2", "U3"] } }, "Orders": { "Keys": { "OrderId": ["O1", "O2"] } } } }

C. { "RequestItems": { "Users": { "FilterExpression": "UserId IN (:u1, :u2, :u3)" }, "Orders": { "FilterExpression": "OrderId IN (:o1, :o2)" } } }

D. { "RequestItems": { "Users": { "AttributesToGet": ["UserId"] }, "Orders": { "AttributesToGet": ["OrderId"] } } }

Solution

1. Step 1: Understand BatchGetItem multi-table request format

   BatchGetItem requires "RequestItems" with each table name mapping to a "Keys" array of key objects.

2. Step 2: Evaluate each option

   { "RequestItems": { "Users": { "Keys": [ { "UserId": { "S": "U1" } }, { "UserId": { "S": "U2" } }, { "UserId": { "S": "U3" } } ] }, "Orders": { "Keys": [ { "OrderId": { "S": "O1" } }, { "OrderId": { "S": "O2" } } ] } } } correctly uses arrays of key objects for both tables. Formats using arrays inside objects, FilterExpression, or AttributesToGet are invalid for BatchGetItem keys.

3. Final Answer:

   { "RequestItems": { "Users": { "Keys": [ { "UserId": { "S": "U1" } }, { "UserId": { "S": "U2" } }, { "UserId": { "S": "U3" } } ] }, "Orders": { "Keys": [ { "OrderId": { "S": "O1" } }, { "OrderId": { "S": "O2" } } ] } } } -> Option A

4. Quick Check:

   Keys array per table = correct multi-table BatchGetItem [OK]

Hint: Use Keys array per table for multi-table BatchGetItem [OK]

Common Mistakes:

• Using FilterExpression instead of Keys
• Passing keys as arrays inside objects incorrectly
• Using AttributesToGet instead of Keys