Query depth and complexity 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 Author { id: ID! name: String! books: [Book!]! } type Book { id: ID! title: String! pages: Int! }

And this query:

{ author(id: "1") { name books { title pages } } }

Assuming the author with id "1" has two books: "GraphQL Basics" (100 pages) and "Advanced GraphQL" (250 pages), what will the query return?

A {"data":{"author":{"name":"Author One","books":[{"title":"GraphQL Basics","pages":100},{"title":"Advanced GraphQL","pages":250}]}}}

B {"data":{"author":{"name":"Author One","books":[{"title":"GraphQL Basics"},{"title":"Advanced GraphQL"}]}}}

C {"errors":[{"message":"Field 'pages' not found on type 'Book'"}]}

D {"data":{"author":{"name":"Author One"}}}

💡 Hint

Think about what fields are requested inside the books field.

The query requests name of the author and for each book, both title and pages. So the response includes all these fields.

🧠 Conceptual

intermediate

Which factor primarily affects GraphQL query complexity?

When designing a GraphQL API, what is the main factor that increases the complexity of a query?

A The number of fields requested and their nesting depth

B The size of the database schema

C The number of mutations in the query

D The number of clients connected simultaneously

💡 Hint

Think about what makes a query take longer to process.

Query complexity depends mainly on how many fields are requested and how deeply nested they are, because each field may require separate data fetching.

📝 Syntax

advanced

Identify the syntax error in this GraphQL query

Find the syntax error in the following GraphQL query:

{ user(id: "2") { name email posts { title content } }

A Missing quotes around the id value

B Using colon instead of equal sign in the argument

C Missing closing curly brace at the end of the query

D Using parentheses instead of braces for the posts field

💡 Hint

Check if all braces are properly closed.

The query is missing the final closing curly brace '}' which is required to close the root selection set.

❓ optimization

advanced

How to reduce GraphQL query complexity effectively?

You have a GraphQL query that fetches deeply nested data causing performance issues. Which approach best reduces query complexity?

A Increase the number of fields requested to get all data at once

B Limit the maximum depth of queries allowed by the server

C Remove all arguments from the query to simplify it

D Use multiple nested fragments to organize the query

💡 Hint

Think about server-side controls to prevent expensive queries.

Limiting query depth on the server prevents clients from requesting too deeply nested data, which reduces complexity and improves performance.

🔧 Debug

expert

Why does this GraphQL query cause a complexity error?

Given this query:

{ library { shelves { books { author { name } } } } }

The server returns an error about query complexity being too high. What is the most likely reason?

A The server does not support nested queries

B The query is missing required arguments for shelves

C The author field does not exist on books type

D The query requests multiple nested levels causing exponential data fetching

💡 Hint

Consider how nested fields multiply the amount of data fetched.

Each nested level increases the amount of data fetched. Deep nesting like shelves → books → author causes high complexity, triggering server limits.