Apollo Server setup in GraphQL - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

Query result from a simple Apollo Server schema

Given this Apollo Server schema and resolver, what will be the output of the query { hello }?

GraphQL

const { ApolloServer, gql } = require('apollo-server');

const typeDefs = gql`
  type Query {
    hello: String
  }
`;

const resolvers = {
  Query: {
    hello: () => 'Hello, world!'
  }
};

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

A { "data": { "hello": "Hello, world!" } }

B { "error": "Field 'hello' not found" }

C { "data": { "hello": "Hi there!" } }

D { "data": { "greeting": "Hello, world!" } }

💡 Hint

Check the resolver function for the hello field.

The resolver for hello returns the string 'Hello, world!'. So the query returns this string under the hello key.

📝 Syntax

intermediate

Identify the syntax error in Apollo Server setup

Which option contains a syntax error in the Apollo Server setup code?

GraphQL

const { ApolloServer, gql } = require('apollo-server');

const typeDefs = gql`
  type Query {
    greet: String
  }
`;

const resolvers = {
  Query: {
    greet: () => 'Hi!'
  }
};

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

A const { ApolloServer, gql } = require('apollo-server');

B const server = new ApolloServer({ typeDefs, resolvers });

C const typeDefs = gql` type Query { greet: String }`

D const resolvers = { Query: { greet() => 'Hi!' } };

💡 Hint

Look at the arrow function syntax inside the resolvers object.

Option D uses incorrect arrow function syntax: greet() => 'Hi!' is invalid. It should be greet: () => 'Hi!'.

❓ optimization

advanced

Optimize Apollo Server startup for large schemas

You have a large schema with many types and resolvers. Which option best improves Apollo Server startup performance?

A Disable introspection to speed up server initialization.

B Load all resolvers and type definitions eagerly at server start.

C Use code splitting and lazy loading for resolvers and typeDefs.

D Use schema stitching to combine multiple small schemas into one.

💡 Hint

Think about loading only what is needed when it is needed.

Lazy loading parts of the schema and resolvers delays loading until necessary, reducing initial startup time.

🧠 Conceptual

advanced

Understanding Apollo Server context function

What is the main purpose of the context function in Apollo Server setup?

A To specify the server port and hostname.

B To provide a shared object accessible by all resolvers during a request.

C To define the GraphQL schema types and fields.

D To handle errors thrown by resolvers.

💡 Hint

Think about what data resolvers might need access to for each request.

The context function creates an object shared by all resolvers for a single request, often used for authentication info or database connections.

🔧 Debug

expert

Debugging Apollo Server resolver error

Given this resolver code, what error will Apollo Server return when querying { user(id: "1") { name } } if the user is not found?

GraphQL

const resolvers = {
  Query: {
    user: (_, { id }) => {
      const user = database.findUserById(id);
      if (!user) {
        throw new Error('User not found');
      }
      return user;
    }
  }
};

A { "data": { "user": null }, "errors": [{ "message": "User not found" }] }

B { "error": "User not found" }

C { "data": { "user": { "name": null } } }

D { "data": null, "errors": [{ "message": "User not found" }] }

💡 Hint

Recall how Apollo Server handles errors thrown in resolvers.

When a resolver throws an error, Apollo Server sets the corresponding field to null in data and adds the error to the errors array.