AppSync with DynamoDB (GraphQL) - Mini Project: Build & Apply

AppSync with DynamoDB (GraphQL)

📖 Scenario: You are building a simple backend for a book store using AWS AppSync and DynamoDB. The store needs to keep track of books with their titles and authors.

🎯 Goal: Create a DynamoDB table and a GraphQL schema to store books with titles and authors and query books by ID using AppSync.

📋 What You'll Learn

Create a DynamoDB table named Books with id as the primary key

Define a GraphQL schema with a Book type containing id, title, and author

Add a query getBookById to fetch a book by its id

Add a mutation addBook to add a new book to the table

💡 Why This Matters

🌍 Real World

This project simulates building a backend for a book store app using AWS AppSync and DynamoDB, common in serverless web and mobile applications.

💼 Career

Understanding how to connect GraphQL APIs with DynamoDB is valuable for cloud developers, backend engineers, and anyone working with AWS serverless technologies.

1

Create DynamoDB Table

Create a DynamoDB table named Books with a primary key called id of type String.

DynamoDB

# Define the DynamoDB table with name 'Books' and primary key 'id' of type String
# Your code here

Hint

Use TableName to name the table and define id as the HASH key with type S for string.

2

Define GraphQL Schema

Define a GraphQL type called Book with fields id (ID!), title (String!), and author (String!).

DynamoDB

TableName: Books
AttributeDefinitions:
  - AttributeName: id
    AttributeType: S
KeySchema:
  - AttributeName: id
    KeyType: HASH
BillingMode: PAY_PER_REQUEST

# Define GraphQL type 'Book' with fields 'id: ID!', 'title: String!', and 'author: String!'
# Your code here

Hint

Use type Book { ... } to define the fields with exclamation marks to mark them as required.

3

Add Query and Mutation

Add a query called getBookById that takes id: ID! and returns a Book. Add a mutation called addBook that takes id: ID!, title: String!, and author: String! and returns a Book.

DynamoDB

TableName: Books
AttributeDefinitions:
  - AttributeName: id
    AttributeType: S
KeySchema:
  - AttributeName: id
    KeyType: HASH
BillingMode: PAY_PER_REQUEST

schema {
  query: Query
  mutation: Mutation
}

type Book {
  id: ID!
  title: String!
  author: String!
}

# Add 'getBookById(id: ID!): Book' to type Query
# Add 'addBook(id: ID!, title: String!, author: String!): Book' to type Mutation
# Your code here

Hint

Define type Query and type Mutation with the specified fields and arguments.

4

Complete AppSync Resolver Mapping

Add the resolver mapping templates for getBookById query and addBook mutation to connect AppSync with the DynamoDB Books table. Use id as the key for getBookById and pass id, title, and author as the item for addBook.

DynamoDB

TableName: Books
AttributeDefinitions:
  - AttributeName: id
    AttributeType: S
KeySchema:
  - AttributeName: id
    KeyType: HASH
BillingMode: PAY_PER_REQUEST

schema {
  query: Query
  mutation: Mutation
}

type Book {
  id: ID!
  title: String!
  author: String!
}

type Query {
  getBookById(id: ID!): Book
}

type Mutation {
  addBook(id: ID!, title: String!, author: String!): Book
}

# Add resolver mapping for 'getBookById' query using 'id' as key
# Add resolver mapping for 'addBook' mutation passing 'id', 'title', and 'author' as item
# Your code here

Hint

Use GetItem operation with id key for the query resolver. Use PutItem with id, title, and author attributes for the mutation resolver.

Practice

1. What is the main benefit of using AWS AppSync with DynamoDB in an application?

easy

A. It allows apps to request only the data they need using GraphQL.

B. It automatically creates SQL tables for data storage.

C. It requires manual scaling of the database.

D. It replaces the need for any backend code.

Solution

1. Step 1: Understand AppSync's role

   AppSync uses GraphQL to let apps ask for exactly the data they need, avoiding over-fetching.

2. Step 2: Understand DynamoDB's role

   DynamoDB stores data quickly and scales automatically, but does not create SQL tables or replace backend code entirely.

3. Final Answer:

   It allows apps to request only the data they need using GraphQL. -> Option A

4. Quick Check:

   AppSync + GraphQL = precise data requests [OK]

Hint: Remember: AppSync uses GraphQL for precise data fetching [OK]

Common Mistakes:

• Thinking DynamoDB creates SQL tables
• Believing manual scaling is needed
• Assuming AppSync removes all backend code

2. Which of the following is the correct way to define a DynamoDB data source in an AWS AppSync GraphQL schema?

easy

A. type Query { getItem(id: ID!): Item @aws_dynamodb(tableName: MyTable) }

B. type Query { getItem(id: ID!): Item @aws_lambda(functionName: "MyFunction") }

C. type Query { getItem(id: ID!): Item @aws_dynamodb(tableName: "MyTable", region: "us-east-1") }

D. type Query { getItem(id: ID!): Item @aws_s3(bucketName: "MyBucket") }

Solution

1. Step 1: Identify the correct directive for DynamoDB

   The @aws_dynamodb directive is used to link a DynamoDB table as a data source in AppSync.

2. Step 2: Check syntax correctness

   type Query { getItem(id: ID!): Item @aws_dynamodb(tableName: "MyTable", region: "us-east-1") } correctly includes the tableName and region parameters, which are valid for specifying the DynamoDB data source.

3. Final Answer:

   type Query { getItem(id: ID!): Item @aws_dynamodb(tableName: "MyTable", region: "us-east-1") } -> Option C

4. Quick Check:

   @aws_dynamodb with tableName and region is correct syntax [OK]

Hint: Look for @aws_dynamodb with tableName and region parameters [OK]

Common Mistakes:

• Using @aws_lambda instead of @aws_dynamodb for DynamoDB
• Forgetting quotes around tableName value
• Using @aws_s3 which is unrelated to DynamoDB

3. Given this GraphQL query in AppSync linked to DynamoDB:

query GetBook { getBook(id: "123") { id title author } }

And the DynamoDB table has an item:

{"id": "123", "title": "Learn DynamoDB", "author": "Jane"}

What will be the output of this query?

medium

A. {"data": {"getBook": {"id": "123", "title": "Learn DynamoDB", "author": "Jane"}}}

B. {"data": {"getBook": null}}

C. {"errors": [{"message": "Item not found"}]}

D. {"data": {"getBook": {"id": "123", "title": null, "author": null}}}

Solution

1. Step 1: Understand the query and data

   The query requests the item with id "123" and fields id, title, author. The table has this exact item.

2. Step 2: Predict the query result

   Since the item exists, the query returns all requested fields with their values.

3. Final Answer:

   {"data": {"getBook": {"id": "123", "title": "Learn DynamoDB", "author": "Jane"}}} -> Option A

4. Quick Check:

   Existing item returns full data [OK]

Hint: If item exists, query returns requested fields with values [OK]

Common Mistakes:

• Assuming null fields if item exists
• Expecting errors when item is present
• Confusing null result with missing item

4. You wrote this resolver mapping template for a DynamoDB getItem operation in AppSync:

{
  "version": "2017-02-28",
  "operation": "GetItem",
  "key": {
    "id": $util.dynamodb.toDynamoDBJson($ctx.args.id)
  }
}

But your query always returns null. What is the likely mistake?

medium

A. The $util.dynamodb.toDynamoDBJson function is not needed.

B. The operation should be "Query" instead of "GetItem".

C. The version "2017-02-28" is outdated and causes errors.

D. The key attribute name "id" does not match the DynamoDB table's primary key name.

Solution

1. Step 1: Check key attribute name

   The key attribute name in the resolver must exactly match the DynamoDB table's primary key name.

2. Step 2: Understand why null is returned

   If the key name is wrong, DynamoDB cannot find the item, so it returns null.

3. Final Answer:

   The key attribute name "id" does not match the DynamoDB table's primary key name. -> Option D

4. Quick Check:

   Key name mismatch causes null result [OK]

Hint: Match key names exactly between resolver and table [OK]

Common Mistakes:

• Using wrong operation type for getItem
• Ignoring key name case sensitivity
• Removing $util.dynamodb.toDynamoDBJson causing syntax errors

5. You want to create a real-time chat app using AppSync and DynamoDB. Which approach best ensures that clients receive new messages instantly without polling?

hard

A. Have clients poll DynamoDB every few seconds for new messages.

B. Use AppSync subscriptions linked to DynamoDB streams to push updates to clients.

C. Use a Lambda function to write messages to DynamoDB and notify clients via email.

D. Store messages in DynamoDB and refresh the UI only when the app restarts.

Solution

1. Step 1: Understand real-time updates in AppSync

   AppSync supports GraphQL subscriptions that can push data to clients when data changes.

2. Step 2: Connect DynamoDB streams to subscriptions

   DynamoDB streams capture table changes and can trigger AppSync subscriptions to notify clients instantly.

3. Step 3: Evaluate other options

   Polling wastes resources, email notifications are slow and unrelated, and UI refresh on restart is not real-time.

4. Final Answer:

   Use AppSync subscriptions linked to DynamoDB streams to push updates to clients. -> Option B

5. Quick Check:

   Subscriptions + DynamoDB streams = instant updates [OK]

Hint: Use subscriptions with DynamoDB streams for real-time data [OK]

Common Mistakes:

• Relying on polling instead of subscriptions
• Using email for real-time notifications
• Ignoring DynamoDB streams integration