Context setup in GraphQL - Mini Project: Build & Apply

GraphQL Context Setup for User Authentication

📋 What You'll Learn

💡 Why This Matters

🌍 Real World

GraphQL context is used in real applications to pass authentication and other request-specific data to resolvers, enabling personalized and secure data access.

💼 Career

Understanding GraphQL context setup is essential for backend developers working with GraphQL APIs, especially in roles involving user authentication and authorization.

1

Define the GraphQL schema with a currentUser query

Create a GraphQL schema string called typeDefs that defines a Query type with a currentUser field returning a User type. Also define the User type with a name field of type String.

GraphQL

const typeDefs = `
  # Your schema definition here
`

Hint

Define type User with a name field, and type Query with currentUser: User.

2

Create a context function that adds a user object

Create a function called context that takes a { req } parameter and returns an object with a user property set to { name: 'Alice' } to simulate an authenticated user.

GraphQL

const typeDefs = `
  type User {
    name: String
  }

  type Query {
    currentUser: User
  }
`;

// Create context function here
// Your code here

Hint

Return an object with user set to { name: 'Alice' } inside the context function.

3

Write resolver for currentUser using context

Create a resolvers object with a Query field. Inside Query, write a currentUser resolver function that takes parent, args, and context parameters and returns context.user.

GraphQL

const typeDefs = `
  type User {
    name: String
  }

  type Query {
    currentUser: User
  }
`;

const context = ({ req }) => {
  return { user: { name: 'Alice' } };
};

// Create resolvers object here
// Your code here

Hint

Return context.user from the currentUser resolver function.

4

Complete server setup with schema, resolvers, and context

Create an ApolloServer instance called server using typeDefs, resolvers, and context. Use new ApolloServer({ typeDefs, resolvers, context }).

GraphQL

const typeDefs = `
  type User {
    name: String
  }

  type Query {
    currentUser: User
  }
`;

const context = ({ req }) => {
  return { user: { name: 'Alice' } };
};

const resolvers = {
  Query: {
    currentUser: (parent, args, context) => {
      return context.user;
    }
  }
};

// Create ApolloServer instance here
// Your code here

Hint

Pass typeDefs, resolvers, and context to the ApolloServer constructor.

Practice

1. What is the main purpose of the context in a GraphQL server?

easy

A. To share data like user info or database clients across all resolvers

B. To define the GraphQL schema types

C. To write the query resolvers

D. To format the GraphQL query response

Solution

1. Step 1: Understand what context provides

   Context is an object that runs once per request and is accessible in every resolver, allowing shared data like user info or database clients.

2. Step 2: Compare with other options

   Defining schema types, writing resolvers, and formatting responses are separate tasks not handled by context.

3. Final Answer:

   To share data like user info or database clients across all resolvers -> Option A

4. Quick Check:

   Context shares data across resolvers [OK]

Hint: Context shares common data across resolvers per request [OK]

Common Mistakes:

• Confusing context with schema definition
• Thinking context formats responses
• Assuming context writes resolver logic

2. Which of the following is the correct way to define a context function in Apollo Server?

easy

A. context = { user: getUser() }

B. context: () => ({ user: getUser() })

C. context: { user: getUser() }

D. context() { return user: getUser() }

Solution

1. Step 1: Recall Apollo Server context syntax

   Context is defined as a function returning an object, e.g., context: () => ({ user: getUser() }).

2. Step 2: Identify syntax errors in other options

   context = { user: getUser() } uses assignment instead of a function, C uses an object directly without a function, and D has invalid syntax missing parentheses and braces.

3. Final Answer:

   context: () => ({ user: getUser() }) -> Option B

4. Quick Check:

   Context is a function returning an object [OK]

Hint: Context must be a function returning an object [OK]

Common Mistakes:

• Defining context as a plain object
• Missing parentheses in function syntax
• Using assignment instead of property

3. Given this context setup in Apollo Server:

context: () => ({ user: { id: 5, name: 'Alice' } })

What will be the value of context.user.name inside a resolver?

medium

A. undefined

B. 5

C. null

D. 'Alice'

Solution

1. Step 1: Analyze the context object

   The context function returns an object with a user property containing { id: 5, name: 'Alice' }.

2. Step 2: Access user.name in resolver

   Accessing context.user.name will give the string 'Alice' as defined.

3. Final Answer:

   'Alice' -> Option D

4. Quick Check:

   context.user.name = 'Alice' [OK]

Hint: Context returns user object; access properties directly [OK]

Common Mistakes:

• Confusing user id with name
• Assuming context is undefined
• Expecting null instead of string

4. You wrote this context function:

context: () => { user: getUser() }

Why does context.user return undefined in resolvers?

medium

A. Because user is not a valid property

B. Because getUser() is undefined

C. Because the function does not return the object explicitly

D. Because context must be an object, not a function

Solution

1. Step 1: Check function return behavior

   The function uses curly braces but lacks a return statement, so it returns undefined by default.

2. Step 2: Understand impact on context

   Since nothing is returned, context.user is undefined in resolvers.

3. Final Answer:

   Because the function does not return the object explicitly -> Option C

4. Quick Check:

   Missing return in function = undefined context [OK]

Hint: Use return or parentheses to return object in arrow function [OK]

Common Mistakes:

• Omitting return in arrow function with braces
• Assuming getUser() is undefined without checking
• Thinking context must be an object, not function

5. You want to add a database client and user info to context for each request. Which is the best way to do this in Apollo Server?

hard

A. context: async () => { const db = await connectDB(); const user = await getUser(); return { db, user }; }

B. context: { db: connectDB(), user: getUser() }

C. context: () => { db: connectDB(); user: getUser(); }

D. context: () => ({ db: connectDB(), user: getUser() })

Solution

1. Step 1: Understand async context needs

   Connecting to a database and fetching user info are asynchronous operations, so context must be async and await these calls.

2. Step 2: Evaluate options for async correctness

   context: async () => { const db = await connectDB(); const user = await getUser(); return { db, user }; } correctly uses async function and awaits results before returning an object. context: { db: connectDB(), user: getUser() } is a plain object, not a function. context: () => { db: connectDB(); user: getUser(); } lacks return and awaits. context: () => ({ db: connectDB(), user: getUser() }) returns an object but does not await async calls.

3. Final Answer:

   context: async () => { const db = await connectDB(); const user = await getUser(); return { db, user }; } -> Option A

4. Quick Check:

   Async context with awaited data [OK]

Hint: Use async function and await for async data in context [OK]

Common Mistakes:

• Not awaiting async calls in context
• Using plain object instead of function
• Missing return statement in function