Schema-first development in GraphQL - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

What is the main advantage of schema-first development in GraphQL?

Consider you are building a GraphQL API. What is the primary benefit of defining the schema before writing any resolver code?

A It forces the API to use REST endpoints internally.

B It automatically generates database tables without any additional setup.

C It eliminates the need for writing any resolver functions.

D It allows frontend and backend teams to agree on data structure early, improving collaboration.

💡 Hint

Think about how defining the shape of data first helps teams work together.

Schema-first development means you design the API's data types and queries upfront. This helps frontend and backend developers understand and agree on the data format early, making collaboration smoother.

❓ query_result

intermediate

What is the output of this GraphQL query given the schema?

Given the schema below, what will be the result of the query?

type Query {
  book(id: ID!): Book
}

type Book {
  id: ID!
  title: String!
  author: String!
}

Query:
{
  book(id: "1") {
    title
    author
  }
}

GraphQL

Assume the data source has a book with id "1", title "1984", and author "George Orwell".

A { "data": { "book": { "title": "1984", "author": "George Orwell" } } }

B { "data": { "book": { "id": "1", "title": "1984" } } }

C { "data": { "book": null } }

D { "errors": [ { "message": "Field 'author' not found" } ] }

💡 Hint

Look at the query fields and the schema's Book type.

The query asks for title and author of the book with id "1". Since the data source has this book, the response includes both fields under data.book.

📝 Syntax

advanced

Identify the syntax error in this GraphQL schema definition

Which option contains the syntax error in the schema below?

type User {
  id: ID!
  name: String!
  email: String!
  friends: [User]
}

type Query {
  user(id: ID!): User
}

GraphQL

Assume the schema is used in a GraphQL server.

A There is no syntax error; the schema is valid.

B The 'friends' field should be '[User]!' to indicate the list is non-null.

C The 'friends' field should be '[User!]!' to indicate a non-null list of non-null Users.

D The 'friends' field should be '[User!]' instead of '[User]'.

💡 Hint

Check the GraphQL list and nullability syntax rules.

The schema is valid. The 'friends' field is a list of User objects that can be null or contain nulls. This is allowed syntax in GraphQL.

❓ optimization

advanced

How to optimize resolver performance in schema-first GraphQL?

You notice your GraphQL API is slow because many resolvers fetch data separately. Which approach best improves performance?

A Remove the schema and write raw SQL queries instead.

B Add more fields to the schema to reduce the number of queries.

C Use data loader pattern to batch and cache database requests in resolvers.

D Use REST endpoints inside resolvers to fetch data.

💡 Hint

Think about how to reduce repeated database calls in resolvers.

Data loader batches multiple requests into one and caches results, reducing database load and improving performance in GraphQL resolvers.

🔧 Debug

expert

Why does this schema-first GraphQL server fail to start?

Given this schema snippet, the server throws an error on startup:

type Query {
  getUser(id: ID!): User
}

type User {
  id: ID!
  name: String!
  bestFriend: User
}

What is the most likely cause?

A The schema has a circular reference with 'User' referencing itself, which is invalid.

B There is no syntax error; the error is likely in resolver implementation.

C The schema is missing a root mutation type, causing startup failure.

D The 'bestFriend' field must be non-nullable with an exclamation mark.

💡 Hint

Think about whether self-referencing types are allowed in GraphQL schemas.

GraphQL supports self-referencing types like 'User' referencing 'User'. The schema is valid. Startup errors usually come from resolver code or server config, not this schema.