Data source integration in GraphQL - Mini Project: Build & Apply

GraphQL Data Source Integration

📖 Scenario: You are building a simple GraphQL API for a bookstore. The data about books is stored in a list of dictionaries. You want to connect this data source to your GraphQL schema so clients can query book information.

🎯 Goal: Create a GraphQL schema that integrates a data source of books and allows querying the list of books with their titles and authors.

📋 What You'll Learn

Create a list called books with three books, each having id, title, and author fields.

Define a GraphQL type Book with fields id, title, and author.

Create a query type Query with a field books that returns the list of books.

Connect the books field resolver to return the books data source.

💡 Why This Matters

🌍 Real World

GraphQL APIs often need to connect to data sources like databases or in-memory lists to serve client queries.

💼 Career

Understanding how to integrate data sources with GraphQL is essential for backend developers building APIs.

1

Create the data source list

Create a list called books with these exact entries: {"id": "1", "title": "The Great Gatsby", "author": "F. Scott Fitzgerald"}, {"id": "2", "title": "1984", "author": "George Orwell"}, and {"id": "3", "title": "To Kill a Mockingbird", "author": "Harper Lee"}.

GraphQL

# Create the books data source list
# Your code here

Hint

Use a Python list of dictionaries to store the book data exactly as shown.

2

Define the GraphQL Book type

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

GraphQL

books = [
    {"id": "1", "title": "The Great Gatsby", "author": "F. Scott Fitzgerald"},
    {"id": "2", "title": "1984", "author": "George Orwell"},
    {"id": "3", "title": "To Kill a Mockingbird", "author": "Harper Lee"}
]

# Define the GraphQL Book type
# Your code here

Hint

Use GraphQL SDL syntax to define the Book type with the required fields and types.

3

Add the Query type with books field

Add a GraphQL Query type with a field books that returns a list of Book objects, using the syntax books: [Book!]!.

GraphQL

books = [
    {"id": "1", "title": "The Great Gatsby", "author": "F. Scott Fitzgerald"},
    {"id": "2", "title": "1984", "author": "George Orwell"},
    {"id": "3", "title": "To Kill a Mockingbird", "author": "Harper Lee"}
]

type_defs = """
type Book {
  id: ID!
  title: String!
  author: String!
}

# Add the Query type with books field
# Your code here
"""

Hint

Extend the GraphQL schema by adding a Query type with a books field that returns a non-null list of non-null Book objects.

4

Connect the books field resolver

Create a resolver dictionary called resolvers with a Query key. Inside Query, add a books function that returns the books list.

GraphQL

books = [
    {"id": "1", "title": "The Great Gatsby", "author": "F. Scott Fitzgerald"},
    {"id": "2", "title": "1984", "author": "George Orwell"},
    {"id": "3", "title": "To Kill a Mockingbird", "author": "Harper Lee"}
]

type_defs = """
type Book {
  id: ID!
  title: String!
  author: String!
}

type Query {
  books: [Book!]!
}
"""

# Create resolvers dictionary with Query.books returning books list
# Your code here

Hint

Define a resolvers dictionary with a Query key. The books resolver should be a function returning the books list.

Practice

1. What is the main purpose of data source integration in GraphQL?

easy

A. To style the GraphQL interface for better user experience

B. To encrypt data sent over the network

C. To create new GraphQL schema types automatically

D. To connect GraphQL queries to the actual data storage or services

Solution

1. Step 1: Understand what data source integration means

   It means linking GraphQL queries to where data is stored or fetched from, like databases or APIs.

2. Step 2: Identify the main goal of this integration

   The goal is to let GraphQL get data from these sources when a query runs.

3. Final Answer:

   To connect GraphQL queries to the actual data storage or services -> Option D

4. Quick Check:

   Data source integration = connect queries to data [OK]

Hint: Think: GraphQL needs to reach data somewhere [OK]

Common Mistakes:

• Confusing integration with UI styling
• Thinking it creates schema types automatically
• Assuming it handles data encryption

2. Which of the following is the correct way to define a resolver that fetches data from a REST API in GraphQL?

easy

A. const resolver = () => fetch('https://api.example.com/data').then(res => res.json());

B. const resolver = fetch('https://api.example.com/data').json();

C. const resolver = () => fetch('https://api.example.com/data').json();

D. const resolver = () => fetch('https://api.example.com/data').then(res => res.text());

Solution

1. Step 1: Check how fetch works in JavaScript

   fetch returns a promise; to get JSON, you call .then(res => res.json()).

2. Step 2: Verify the resolver syntax

   const resolver = () => fetch('https://api.example.com/data').then(res => res.json()); correctly returns a function that fetches and parses JSON asynchronously.

3. Final Answer:

   const resolver = () => fetch('https://api.example.com/data').then(res => res.json()); -> Option A

4. Quick Check:

   fetch + then + json() = correct resolver [OK]

Hint: Remember fetch returns a promise; use then() to parse JSON [OK]

Common Mistakes:

• Calling .json() directly on fetch without then()
• Not wrapping fetch in a function
• Using res.text() instead of res.json() for JSON data

3. Given this resolver code snippet, what will be the output of the GraphQL query if the API returns [{"id":1,"name":"Alice"}]?

const resolvers = {
  Query: {
    users: async () => {
      const response = await fetch('https://api.example.com/users');
      const data = await response.json();
      return data;
    }
  }
};

medium

A. undefined

B. {"id":1,"name":"Alice"}

C. [{"id":1,"name":"Alice"}]

D. Error: fetch is not defined

Solution

1. Step 1: Analyze the resolver's return value

   The resolver awaits the fetch, parses JSON, and returns the data array as is.

2. Step 2: Match the returned data with the query output

   The API returns an array with one user object, so the query returns the same array.

3. Final Answer:

   [{"id":1,"name":"Alice"}] -> Option C

4. Quick Check:

   Returned data array = output array [OK]

Hint: Async resolver returns exactly what API sends after parsing [OK]

Common Mistakes:

• Assuming it returns a single object instead of an array
• Forgetting async/await means data is resolved
• Thinking fetch is undefined in server environment

4. Identify the error in this resolver code that fetches data from a database:

const resolvers = {
  Query: {
    products: () => {
      const data = db.query('SELECT * FROM products');
      return data;
    }
  }
};

medium

A. The resolver should be async and await the db query

B. The query string is incorrect SQL syntax

C. The resolver should return a promise, not data

D. The resolver is missing a try-catch block

Solution

1. Step 1: Understand db.query behavior

   db.query usually returns a promise, so it must be awaited in async functions.

2. Step 2: Check resolver function signature

   The resolver is not async and does not await the promise, so it returns a pending promise instead of data.

3. Final Answer:

   The resolver should be async and await the db query -> Option A

4. Quick Check:

   Async + await needed for promises [OK]

Hint: If db query returns promise, resolver must be async and await it [OK]

Common Mistakes:

• Ignoring async/await for promises
• Assuming SQL syntax is wrong without checking
• Thinking try-catch is mandatory for correctness

5. You want to integrate two data sources in a GraphQL resolver: a REST API and a SQL database. Which approach correctly combines data from both sources before returning it?

const resolvers = {
  Query: {
    combinedData: async () => {
      const apiData = await fetch('https://api.example.com/items').then(res => res.json());
      const dbData = await db.query('SELECT * FROM items');
      // What next?
    }
  }
};

hard

A. Return {apiData, dbData} as an object without merging

B. Return [...apiData, ...dbData] to merge both arrays

C. Return dbData only, ignoring apiData

D. Return apiData only, ignoring dbData

Solution

1. Step 1: Understand data types returned

   Both apiData and dbData are arrays of items fetched asynchronously.

2. Step 2: Combine arrays before returning

   Using spread syntax [...apiData, ...dbData] merges both arrays into one list.

3. Final Answer:

   Return [...apiData, ...dbData] to merge both arrays -> Option B

4. Quick Check:

   Spread arrays to combine data sources [OK]

Hint: Use spread operator to merge arrays from multiple sources [OK]

Common Mistakes:

• Returning only one data source ignoring the other
• Returning an object without merging arrays
• Forgetting to await both data sources