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.