Entity references in GraphQL - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What is the output of this GraphQL query with entity references?

Given the schema where Book has a reference to Author by ID, what does this query return?

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

GraphQL

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

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

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

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

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

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

D SyntaxError: Cannot query field "author" on type "Book".

💡 Hint

Remember that entity references allow nested queries to fetch related data.

The query fetches a book with ID "1" and its author details. Since the author reference exists, the nested author { name } returns the author's name.

🧠 Conceptual

intermediate

Which statement correctly describes entity references in GraphQL?

Choose the correct description of how entity references work in GraphQL schemas.

A Entity references allow one type to include fields that link to another type, enabling nested queries.

B Entity references automatically duplicate data from one type into another to avoid joins.

C Entity references prevent querying nested objects to improve performance.

D Entity references are only used for scalar fields like strings and numbers.

💡 Hint

Think about how GraphQL lets you fetch related data in one query.

Entity references let one type include fields that point to another type, so you can query nested related data in a single request.

📝 Syntax

advanced

Identify the syntax error in this GraphQL schema with entity references

Which option correctly fixes the syntax error in this schema snippet?

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

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

schema {
  query: Query
}

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

GraphQL

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

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

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

schema {
  query: Query
}

A Change 'schema { query: Query }' to 'schema { query: Query! }'.

B Add exclamation mark to 'author: Author!' in Book type.

C No syntax error; schema is valid.

D Replace 'book(id: ID!): Book' with 'book(id: ID!): [Book]'.

💡 Hint

Check if the schema declaration and types follow GraphQL syntax rules.

The schema is valid as is. The 'schema' block correctly declares the query type. The 'author' field is optional, which is allowed. No syntax errors exist.

❓ optimization

advanced

How to optimize fetching entity references in GraphQL to reduce data size?

You want to fetch books and their authors but minimize data transfer. Which query modification best achieves this?

{
  books {
    title
    author {
      name
      biography
    }
  }
}

A Replace 'author' field with 'authorId' scalar to avoid nested query.

B Use fragments to fetch all author fields to avoid multiple queries.

C Add 'limit: 10' argument to books query to fetch fewer books.

D Remove 'biography' field from author selection to fetch only 'name'.

💡 Hint

Think about selecting only the fields you need to reduce data size.

Removing unnecessary fields like 'biography' reduces the amount of data returned, optimizing the query.

🔧 Debug

expert

Why does this GraphQL query fail when fetching entity references?

Given this query:

{
  book(id: "2") {
    title
    author {
      name
    }
  }
}

And the schema where author is a non-nullable field, why might this query return an error?

GraphQL

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

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

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

A The query syntax is invalid because 'author' cannot be nested inside 'book'.

B The book with id "2" exists but its author reference is missing, causing a null error on a non-nullable field.

C The schema does not define the 'author' type, causing a type error.

D The 'book' query must return a list, not a single object.

💡 Hint

Consider what happens if a required field is missing data.

If the book exists but its author reference is missing (null), the query fails because 'author' is marked as non-nullable, so GraphQL cannot return null for it.