Context setup in GraphQL - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

What is the purpose of context in GraphQL?

In GraphQL, what is the main role of the context object during query execution?

A It caches query results to improve performance automatically.

B It defines the schema types and fields for the GraphQL server.

C It stores shared data like authentication info accessible to all resolvers during a request.

D It handles client-side state management for UI components.

💡 Hint

Think about what data resolvers need to share during a single request.

The context object is created per request and holds shared data like user authentication, database connections, or loaders. This allows resolvers to access common info without passing it explicitly.

❓ query_result

intermediate

What is the output when accessing context in a resolver?

Given this resolver snippet, what will be the value of userId?

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

// Context setup:
const context = { userId: 42 };

A null

B 42

C Throws an error

D undefined

💡 Hint

Look at what the context object contains and what the resolver returns.

The resolver returns context.userId. Since the context object has userId: 42, the output is 42.

📝 Syntax

advanced

Identify the syntax error in context setup

Which option contains a syntax error in setting up the GraphQL context function?

const server = new ApolloServer({
  typeDefs,
  resolvers,
  context: ???
});

A { user: getUser() }

B () => { return { user: getUser() }; }

C context() { return { user: getUser() }; }

D async () => { const user = await getUser(); return { user }; }

💡 Hint

The context option expects a function, not a plain object.

Option A provides a plain object instead of a function. The context option must be a function returning the context object, so D causes a syntax or runtime error.

❓ optimization

advanced

Best practice for expensive context data

You want to add a database connection to the context for each request. Which approach is best to avoid performance issues?

A Create a new database connection inside the context function for every request.

B Reuse a single global database connection shared across all requests in the context.

C Create a new database connection inside each resolver instead of context.

D Create a new database connection once and store it in a global variable, then use it in context.

💡 Hint

Think about connection overhead and sharing resources safely.

Creating a new connection per request (C) is expensive. Reusing a global connection (B) can cause concurrency issues. Creating once and reusing (A) balances performance and safety. Creating in resolvers (D) is inefficient.

🔧 Debug

expert

Why does context data not appear in resolvers?

You set up context as context: () => ({ user: null }). But in resolvers, context.user is always undefined. What is the cause?

A The resolver signature is missing the context parameter.

B The context function is not called because it is missing parentheses in the server setup.

C The context function is asynchronous but not awaited, causing <code>undefined</code> values.

D The context function returns an object with <code>user</code> set to null, so <code>undefined</code> is impossible.

💡 Hint

Check how the resolver accesses context.

If the resolver does not include the context parameter, it cannot access context data, so context.user is undefined. The context function setup is correct.

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