MongoDB with GraphQL - Mini Project: Build & Apply

Build a Simple MongoDB GraphQL API

📖 Scenario: You are creating a small API for a bookstore. The data will be stored in MongoDB, and you will use GraphQL to query and manage the books.This project will guide you step-by-step to set up the data structure, configure the schema, write the main query, and complete the API setup.

🎯 Goal: Build a basic GraphQL API connected to MongoDB that allows querying a list of books with their titles and authors.

📋 What You'll Learn

Create a MongoDB collection with sample book data

Define a GraphQL schema with a Book type

Write a GraphQL query to fetch all books

Complete the API setup to connect schema and resolver

💡 Why This Matters

🌍 Real World

Many modern web applications use GraphQL APIs backed by MongoDB to efficiently query and manage data.

💼 Career

Understanding how to connect GraphQL with MongoDB is valuable for backend developers building flexible and scalable APIs.

1

DATA SETUP: Create MongoDB collection with sample books

Create a MongoDB collection called books with these exact documents: { title: "The Hobbit", author: "J.R.R. Tolkien" } and { title: "1984", author: "George Orwell" }.

GraphQL

// Insert the two book documents into the 'books' collection
// Your code here

Hint

Use insertMany on the books collection to add the two book documents.

2

CONFIGURATION: Define GraphQL Book type

Define a GraphQL type called Book with two fields: title and author, both of type String!.

GraphQL

type Book {
  # Define title and author fields here
  # Your code here
}

Hint

Use type Book { title: String! author: String! } to define the type.

3

CORE LOGIC: Write a GraphQL query to fetch all books

Add a Query type with a field books that returns a list of Book objects: [Book!]!.

GraphQL

type Query {
  # Add books field returning list of Book
  # Your code here
}

Hint

Define type Query { books: [Book!]! } to allow fetching all books.

4

COMPLETION: Connect resolver to fetch books from MongoDB

Write a resolver function for Query.books that returns all documents from the books MongoDB collection using db.collection('books').find().toArray().

GraphQL

const resolvers = {
  Query: {
    // Add resolver for books here
    // Your code here
  }
};

Hint

Use an async resolver function that calls db.collection('books').find().toArray() to get all books.

Practice

1. What is the main purpose of using GraphQL with MongoDB?

easy

A. To store data in tables instead of documents

B. To replace MongoDB with a SQL database

C. To automatically backup MongoDB data

D. To query only the specific data fields needed from MongoDB

Solution

1. Step 1: Understand GraphQL's role

   GraphQL allows clients to request exactly the data they want, no more, no less.

2. Step 2: Connect to MongoDB data

   MongoDB stores flexible documents, and GraphQL queries these documents precisely.

3. Final Answer:

   To query only the specific data fields needed from MongoDB -> Option D

4. Quick Check:

   GraphQL queries = precise data retrieval [OK]

Hint: GraphQL fetches only requested fields from MongoDB [OK]

Common Mistakes:

• Thinking GraphQL replaces MongoDB
• Confusing document storage with tables
• Assuming GraphQL handles backups

2. Which of the following is the correct way to define a GraphQL query to fetch a list of users from MongoDB?

easy

A. query { users { id name email } }

B. mutation { users { id name email } }

C. query users { id name email }

D. fetch users from MongoDB

Solution

1. Step 1: Identify GraphQL query syntax

   GraphQL queries start with the keyword query followed by the selection set.

2. Step 2: Check the options

   query { users { id name email } } correctly uses query { users { id name email } } to fetch user fields.

3. Final Answer:

   query { users { id name email } } -> Option A

4. Quick Check:

   GraphQL query syntax = query + selection set [OK]

Hint: Queries start with 'query' keyword, mutations with 'mutation' [OK]

Common Mistakes:

• Using mutation instead of query for fetching data
• Omitting braces or keywords
• Writing invalid syntax like 'fetch users from MongoDB'

3. Given this GraphQL query to fetch a user by ID:
query { user(id: "123") { name age } }
And MongoDB has a user document { _id: "123", name: "Alice", age: 30, city: "NY" }, what will be the query result?

medium

A. { "data": { "user": { "name": "Alice", "age": 30 } } }

B. { "data": { "user": { "name": "Alice", "city": "NY" } } }

C. { "data": { "user": { "id": "123", "name": "Alice" } } }

D. { "error": "User not found" }

Solution

1. Step 1: Understand the query fields

   The query requests only name and age fields for user with id "123".

2. Step 2: Match MongoDB document fields

   The document has those fields: name "Alice" and age 30, so those are returned.

3. Final Answer:

   { "data": { "user": { "name": "Alice", "age": 30 } } } -> Option A

4. Quick Check:

   Requested fields returned exactly [OK]

Hint: GraphQL returns only requested fields, ignoring others [OK]

Common Mistakes:

• Expecting all document fields returned
• Confusing id with _id field
• Assuming error when user exists

4. You wrote this GraphQL mutation to add a new user:
mutation { addUser(name: "Bob", age: "25") { id name } }
But you get an error: "Field 'addUser' argument 'age' of type 'Int!' was provided invalid value." What is the likely cause?

medium

A. The mutation syntax is incorrect; should use query instead

B. The age argument is missing in the schema definition

C. The age argument was provided as a string, not an integer

D. The age value 25 is invalid because it is too low

Solution

1. Step 1: Analyze the error message

   The error says the 'age' argument type is 'Int!' but the value is invalid.

2. Step 2: Analyze the query literal

   The query provides age: "25" as a string literal, but the schema expects an integer literal for Int!, causing the invalid value error.

3. Final Answer:

   The age argument was provided as a string, not an integer -> Option C

4. Quick Check:

   Type mismatch in argument causes invalid value error [OK]

Hint: Match argument types exactly as schema defines [OK]

Common Mistakes:

• Using query instead of mutation for data change
• Ignoring schema argument types
• Assuming numeric values are always valid

5. You want to update a user's city in MongoDB using GraphQL. The schema defines a mutation:
updateUser(id: ID!, city: String!): User
Which resolver code snippet correctly updates the city field in MongoDB?

hard

A. return UserModel.updateOne({ id }, { city });

B. return UserModel.findByIdAndUpdate(id, { city }, { new: true });

C. return UserModel.findOneAndDelete({ _id: id });

D. return UserModel.insertOne({ id, city });

Solution

1. Step 1: Identify correct MongoDB update method

   findByIdAndUpdate updates a document by its _id and returns the updated document.

2. Step 2: Check options for update and return

   return UserModel.findByIdAndUpdate(id, { city }, { new: true }); uses findByIdAndUpdate with { new: true } to return updated user, matching schema.

3. Final Answer:

   return UserModel.findByIdAndUpdate(id, { city }, { new: true }); -> Option B

4. Quick Check:

   Use findByIdAndUpdate to update and return new doc [OK]

Hint: Use findByIdAndUpdate with { new: true } to get updated doc [OK]

Common Mistakes:

• Using updateOne without returning updated document
• Deleting instead of updating
• Inserting new document instead of updating existing