Code generation from schema in GraphQL - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What is the output of this GraphQL query?

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: Author!
}

type Author {
  id: ID!
  name: String!
}

Query:

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

Assuming the data has a book with id "1", title "GraphQL Basics", and author name "Alice".

A {"errors": [{"message": "Field 'author' must be an object"}]}

B {"data": {"book": {"title": "GraphQL Basics", "author": "Alice"}}}

C {"data": {"book": {"title": "GraphQL Basics"}}}

D {"data": {"book": {"title": "GraphQL Basics", "author": {"name": "Alice"}}}}

💡 Hint

Remember that nested objects must be returned as objects, not strings.

The query requests the book's title and the author's name as a nested object. The correct output nests the author as an object with a name field.

🧠 Conceptual

intermediate

Which GraphQL schema type correctly represents a list of books?

You want to define a field books in your Query type that returns a list of Book objects. Which schema definition is correct?

A books: Book[]

B books: List<Book>

C books: [Book]

D books: {Book}

💡 Hint

GraphQL uses square brackets to denote lists.

In GraphQL schema language, lists are represented by square brackets around the type, e.g., [Book].

📝 Syntax

advanced

Identify the syntax error in this GraphQL schema snippet

Which option contains a syntax error in this GraphQL schema snippet?

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

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

A

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

B

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

C

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

D

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

💡 Hint

Check the syntax for field declarations in GraphQL schema.

Option A is missing a colon between the field name and its type, which is required in GraphQL schema.

❓ optimization

advanced

How to optimize a GraphQL query to avoid over-fetching?

You have a query fetching user with all fields including posts and each post's comments. You only need the user's name and the titles of their posts. Which query is optimized?

A { user(id: "1") { name posts { title } } }

B { user(id: "1") { id name email posts { id title content comments { id text } } } }

C { user(id: "1") { posts { title } } }

D { user(id: "1") { name posts { title comments { text } } } }

💡 Hint

Only request the fields you need to reduce data transfer.

Option A requests only the user's name and the titles of posts, avoiding unnecessary fields and nested comments.

🔧 Debug

expert

Why does this GraphQL query return an error?

Given the schema:

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

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

type Author {
  id: ID!
  name: String!
}

Why does this query cause an error?

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

A Because the query is missing a mutation keyword

B Because 'author' is an object type and must have subfields selected

C Because 'title' is not a valid field of 'Book'

D Because 'book' requires a list of IDs, not a single ID

💡 Hint

In GraphQL, object fields require specifying subfields.

The 'author' field is an object type, so you must specify which fields of 'author' you want. Omitting subfields causes an error.