Expressions with SDK helpers in DynamoDB - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a condition expression that checks if the attribute "status" equals "active".

DynamoDB

const condition = Attr('status').[1]('active');

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

Aeq

Bne

Clt

Dcontains

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'ne' which means 'not equal' instead of 'eq'.

Using 'contains' which checks for substring, not equality.

The eq method creates a condition expression that checks if the attribute equals the given value.

2fill in blank

medium

Complete the code to create a filter expression that checks if the attribute "age" is greater than 30.

DynamoDB

const filter = Attr('age').[1](30);

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

Alt

Bgt

Ceq

DbeginsWith

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'lt' which means 'less than' instead of 'greater than'.

Using 'beginsWith' which is for strings, not numbers.

The gt method creates a condition expression that checks if the attribute is greater than the given value.

3fill in blank

hard

Fix the error in the code to check if the attribute "name" begins with "A".

DynamoDB

const condition = Attr('name').[1]('A');

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

Aeq

Bcontains

CbeginsWith

Dgt

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'contains' which checks anywhere in the string, not just the start.

Using 'eq' which checks for exact match.

The beginsWith method checks if a string attribute starts with the given substring.

4fill in blank

hard

Fill both blanks to create a condition expression that checks if "score" is between 50 and 100.

DynamoDB

const condition = Attr('score').[1](50).[2](100);

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

Abetween

Beq

Cne

Dgt

Attempts:

3 left

💡 Hint

Common Mistakes

Using different methods for the two values instead of 'between'.

Using 'eq' or 'ne' which check equality, not range.

The between method is used with two values to check if an attribute is within a range.

5fill in blank

hard

Fill all three blanks to create a filter expression that checks if "category" equals "books" and "price" is less than 20.

DynamoDB

const filter = Attr([1]).[2]('books').and(Attr([3]).lt(20));

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

A'category'

Beq

C'price'

Dgt

Attempts:

3 left

💡 Hint

Common Mistakes

Using attribute names without quotes.

Using 'gt' instead of 'lt' for price comparison.

Using wrong method instead of 'eq' for equality.

We check if the 'category' attribute equals 'books' using eq, and if 'price' is less than 20 using lt.

Practice

1. What is the main purpose of using SDK helpers for expressions in DynamoDB?

easy

A. To safely build expressions and avoid syntax errors

B. To speed up the network connection to DynamoDB

C. To automatically create tables in DynamoDB

D. To encrypt data stored in DynamoDB

Solution

1. Step 1: Understand what expressions do

   Expressions tell DynamoDB what data to read or write and how to filter or update it.

2. Step 2: Role of SDK helpers

   SDK helpers help build these expressions safely, avoiding syntax mistakes and making code clearer.

3. Final Answer:

   To safely build expressions and avoid syntax errors -> Option A

4. Quick Check:

   SDK helpers = safe expressions [OK]

Hint: Helpers build expressions safely and clearly [OK]

Common Mistakes:

• Thinking SDK helpers speed up network
• Confusing helpers with table creation
• Assuming helpers encrypt data

2. Which of the following is the correct way to import the DynamoDB DocumentClient and ExpressionAttributeNames helper in JavaScript SDK v3?

easy

A. import { DynamoDBDocumentClient } from "aws-sdk";

B. import { DynamoDBClient, ExpressionAttributeNames } from "@aws-sdk/client-dynamodb";

C. const { DynamoDBClient, ExpressionAttributeNames } = require("aws-sdk");

D. import { DynamoDBDocumentClient, ExpressionAttributeNames } from "@aws-sdk/lib-dynamodb";

Solution

1. Step 1: Identify correct SDK package for helpers

   Expression helpers like ExpressionAttributeNames are in "@aws-sdk/lib-dynamodb", not "@aws-sdk/client-dynamodb".

2. Step 2: Correct import syntax for v3

   Use ES module import syntax with curly braces from "@aws-sdk/lib-dynamodb" for DocumentClient and helpers.

3. Final Answer:

   import { DynamoDBDocumentClient, ExpressionAttributeNames } from "@aws-sdk/lib-dynamodb"; -> Option D

4. Quick Check:

   Helpers come from lib-dynamodb package [OK]

Hint: Helpers are in lib-dynamodb, not client-dynamodb [OK]

Common Mistakes:

• Importing helpers from client-dynamodb package
• Using require() instead of import in v3
• Importing from aws-sdk (v2) instead of @aws-sdk

3. Given the following code snippet using DynamoDB SDK helpers, what will be the value of the UpdateExpression string?

const { UpdateExpression, ExpressionAttributeNames, ExpressionAttributeValues } = DynamoDBDocumentClient.update({
  TableName: "Users",
  Key: { userId: "123" },
  UpdateExpression: "set #n = :name",
  ExpressionAttributeNames: { "#n": "name" },
  ExpressionAttributeValues: { ":name": "Alice" }
});
console.log(UpdateExpression);

medium

A. SyntaxError

B. "set #n = :name"

C. "set #name = :name"

D. "set name = :name"

Solution

1. Step 1: Understand UpdateExpression usage

   The UpdateExpression uses placeholders like #n for attribute names and :name for values.

2. Step 2: Check what is logged

   The code logs the UpdateExpression string exactly as set: "set #n = :name" without substitution.

3. Final Answer:

   "set #n = :name" -> Option B

4. Quick Check:

   UpdateExpression logs raw string with placeholders [OK]

Hint: UpdateExpression logs placeholders, not replaced names [OK]

Common Mistakes:

• Expecting placeholders to be replaced in string
• Confusing attribute names with values
• Assuming syntax error due to placeholders

4. You wrote this update expression using SDK helpers but get an error: "ExpressionAttributeNames contains invalid key: #name". What is the likely cause?

UpdateExpression: "set #name = :val",
ExpressionAttributeNames: { "name": "username" },
ExpressionAttributeValues: { ":val": "Bob" }

medium

A. ExpressionAttributeNames keys must start with #

B. ExpressionAttributeValues keys must start with #

C. UpdateExpression should not use placeholders

D. ExpressionAttributeNames values must start with :

Solution

1. Step 1: Check ExpressionAttributeNames format

   Keys in ExpressionAttributeNames must start with # to match placeholders in UpdateExpression.

2. Step 2: Identify mismatch

   The key "name" lacks #, causing invalid key error.

3. Final Answer:

   ExpressionAttributeNames keys must start with # -> Option A

4. Quick Check:

   Attribute name keys start with # [OK]

Hint: Attribute name keys always start with # [OK]

Common Mistakes:

• Using keys without # in ExpressionAttributeNames
• Confusing keys in ExpressionAttributeValues
• Removing placeholders from UpdateExpression

5. You want to update a DynamoDB item to increment a numeric attribute "score" by 5 using SDK helpers. Which code snippet correctly builds the UpdateExpression and attribute values?

hard

A. UpdateExpression: "set score = score + :inc",
ExpressionAttributeValues: { ":inc": 5 }

B. UpdateExpression: "add score :inc",
ExpressionAttributeValues: { ":inc": 5 }

C. UpdateExpression: "set #s = #s + :inc",
ExpressionAttributeNames: { "#s": "score" },
ExpressionAttributeValues: { ":inc": 5 }

D. UpdateExpression: "increment score by 5"

Solution

1. Step 1: Use placeholders for attribute names

   Since "score" is an attribute name, use ExpressionAttributeNames with #s placeholder.

2. Step 2: Build UpdateExpression correctly

   Use "set #s = #s + :inc" to increment score by value in :inc.

3. Step 3: Provide ExpressionAttributeValues

   Set ":inc" to 5 to add 5 to score.

4. Final Answer:

   UpdateExpression: "set #s = #s + :inc", ExpressionAttributeNames: { "#s": "score" }, ExpressionAttributeValues: { ":inc": 5 } -> Option C

5. Quick Check:

   Use placeholders for names and values [OK]

Hint: Use # for names and : for values in expressions [OK]

Common Mistakes:

• Not using ExpressionAttributeNames for attribute names
• Using unsupported syntax like 'increment score by 5'
• Using 'add' without placeholders