Bidirectional relationships in GraphQL - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

Querying a bidirectional relationship

Given a GraphQL schema where Author has a list of Book objects and each Book has a reference back to its Author, what will be the output of this query?

query {
  authors {
    name
    books {
      title
      author {
        name
      }
    }
  }
}

GraphQL

type Author {
  id: ID!
  name: String!
  books: [Book!]!
}

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

# Sample data:
# Author: {id: "1", name: "Alice", books: [Book1, Book2]}
# Book1: {id: "101", title: "GraphQL Basics", author: Author}
# Book2: {id: "102", title: "Advanced GraphQL", author: Author}

A [{"name": "Alice", "books": [{"title": "GraphQL Basics", "author": {"name": "Alice"}}, {"title": "Advanced GraphQL", "author": {"name": "Alice"}}]}]

B [{"name": "Alice", "books": [{"title": "GraphQL Basics", "author": null}, {"title": "Advanced GraphQL", "author": null}]}]

C [{"name": "Alice", "books": [{"title": "GraphQL Basics"}, {"title": "Advanced GraphQL"}]}]

D [{"name": "Alice", "books": null}]

💡 Hint

Think about how the bidirectional link allows nested querying of author inside each book.

The query fetches authors, their books, and for each book, the author again. Because of the bidirectional relationship, the author inside each book is populated with the author's name.

🧠 Conceptual

intermediate

Understanding bidirectional relationships in GraphQL

Which statement best describes a bidirectional relationship in GraphQL schemas?

A Types are unrelated and cannot reference each other in queries.

B A type references itself recursively without involving other types.

C Two types reference each other, allowing queries to navigate from one to the other and back.

D A type has a list of scalar values only, without referencing other types.

💡 Hint

Think about how you can traverse data in both directions in a schema.

Bidirectional relationships mean two types have fields referencing each other, enabling queries to go from one type to the other and back.

📝 Syntax

advanced

Identify the syntax error in bidirectional schema definition

Which option contains a syntax error in defining a bidirectional relationship between Author and Book?

GraphQL

type Author {
  id: ID!
  name: String!
  books: [Book!]!
}

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

A

type Author {
  id: ID!
  name: String!
  books: [Book]
}

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

B

type Author {
  id: ID!
  name: String!
  books: [Book!]!
}

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

C

type Author {
  id: ID!
  name: String!
  books: [Book!]!
}

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

D

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

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

💡 Hint

Check the type of the books field in Author. Should it be a list or a single object?

The books field should be a list of Book objects, not a single Book. Option D incorrectly defines it as a single Book without list brackets.

❓ optimization

advanced

Optimizing nested queries in bidirectional relationships

You have a bidirectional relationship between Author and Book. You want to fetch authors and their books but avoid redundant nested author data inside each book to reduce query size. Which query modification achieves this?

A Remove the nested <code>author</code> field inside <code>books</code> in the query.

B Add <code>@skip(if: true)</code> directive to the <code>author</code> field inside <code>books</code>.

C Use fragments to fetch <code>author</code> inside <code>books</code>.

D Fetch only <code>books</code> without any fields.

💡 Hint

Think about how to avoid fetching nested data you don't need.

Removing the nested author field inside books prevents fetching redundant author data, reducing query size and improving performance.

🔧 Debug

expert

Debugging infinite recursion in bidirectional GraphQL query

Consider this GraphQL query on a bidirectional schema:

query {
  authors {
    name
    books {
      title
      author {
        books {
          title
        }
      }
    }
  }
}

What problem will this query cause when executed?

A It will cause a syntax error due to nested fields.

B It will cause infinite recursion leading to a server error or timeout.

C It will return an empty list because of missing fields.

D It will return only the first author and their books without errors.

💡 Hint

Think about how the query keeps nesting author and books inside each other.

The query nests author inside books and then books inside author again, causing infinite recursion. This leads to server errors or timeouts.