Field selection in GraphQL - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What is the output of this GraphQL query?

Given the following GraphQL schema snippet:

type Book {
  title: String
  author: Author
}

type Author {
  name: String
  age: Int
}

And the query:

{
  book {
    title
    author {
      name
    }
  }
}

What fields will be included in the response?

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

B {"data": {"book": {"title": "1984", "author": {"name": "George Orwell", "age": 46}}}}

C {"data": {"book": {"title": "1984"}}}

D {"data": {"book": {"author": {"name": "George Orwell"}}}}

💡 Hint

Look carefully at which fields are requested inside author.

The query asks for title and inside author only name. So the response includes those fields only.

📝 Syntax

intermediate

Which GraphQL query has a syntax error?

Identify the query that will cause a syntax error when executed.

A { book { title author name } }

B { book { title author { name age } } }

C } } } eman { rohtua eltit { koob {

D { book { title author { name } } }

💡 Hint

Remember that nested fields must be enclosed in braces.

Option A tries to select author and name at the same level without nesting name inside author. This is invalid syntax.

❓ optimization

advanced

Which query is the most efficient to fetch only book titles?

You want to fetch only the titles of all books. Which query is best to minimize data transfer?

A { books { title author { name } } }

B { books { title author { name age } } }

C { books { title author } }

D { books { title } }

💡 Hint

Request only the fields you need.

Option D requests only title for each book, minimizing data sent. Other options request extra fields unnecessarily.

🧠 Conceptual

advanced

What happens if you omit a field in a GraphQL query?

Consider a GraphQL type User with fields id, name, and email. If you query only id and name, what will the server return for email?

A The server returns the email field with its value.

B The server returns null for the email field.

C The server omits the email field entirely from the response.

D The server returns an error because email was not requested.

💡 Hint

GraphQL only returns fields explicitly requested.

If a field is not requested in the query, the server does not include it in the response at all.

🔧 Debug

expert

Why does this GraphQL query return an error?

Given the schema:

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

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

And the query:

{
  user(id: "1") {
    id
    name
    friends {
      id
      name
      friends {
        id
      }
    }
  }
}

The server returns an error about exceeding query depth. Why?

A The query is missing required arguments for friends field.

B The query requests nested friends fields recursively, causing too deep nesting.

C The query uses invalid field names for User type.

D The query syntax is incorrect due to missing braces.

💡 Hint

Think about how deep the query goes into nested fields.

The query requests friends of friends of friends, which can cause very deep recursion. Many GraphQL servers limit query depth to prevent abuse.