One-to-many relationships in GraphQL - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

Querying a one-to-many relationship in GraphQL

Given a GraphQL schema where Author has many Books, what will be the result of this query?

query {
  authors {
    name
    books {
      title
    }
  }
}

GraphQL

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

type Book {
  id: ID!
  title: String!
  authorId: ID!
}

# Sample data:
# authors = [{id: "1", name: "Alice"}, {id: "2", name: "Bob"}]
# books = [{id: "a", title: "GraphQL Basics", authorId: "1"}, {id: "b", title: "Advanced GraphQL", authorId: "1"}, {id: "c", title: "Intro to Databases", authorId: "2"}]

A [{"name": "Alice", "books": [{"title": "GraphQL Basics"}, {"title": "Advanced GraphQL"}]}, {"name": "Bob", "books": [{"title": "Intro to Databases"}]}]

B [{"name": "Alice", "books": [{"title": "Intro to Databases"}]}, {"name": "Bob", "books": [{"title": "GraphQL Basics"}, {"title": "Advanced GraphQL"}]}]

C [{"name": "Alice", "books": []}, {"name": "Bob", "books": []}]

D [{"name": "Alice"}, {"name": "Bob"}]

💡 Hint

Remember that books are linked to authors by authorId.

The query returns each author with their books. Alice has two books, Bob has one.

🧠 Conceptual

intermediate

Understanding one-to-many relationships in GraphQL schema

Which statement correctly describes a one-to-many relationship in a GraphQL schema?

A A type has no fields referencing other types.

B A type has a field that returns a single scalar value only.

C A type has a field that returns a union of unrelated types.

D A type has a field that returns a list of another type, representing multiple related items.

💡 Hint

Think about how multiple related items are represented.

One-to-many means one item relates to many items of another type, so the field returns a list.

📝 Syntax

advanced

Identify the syntax error in this GraphQL schema for one-to-many

Which option contains a syntax error in defining a one-to-many relationship?

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

type Book {
  id: ID!
  title: String!
  authorId: ID!
}

A The field 'authorId' should be a list type '[ID!]' instead of 'ID!'.

B The field 'books' should be a list type '[Book!]' instead of 'Book!'.

C The type 'Book' must have a field 'author' of type 'Author!'.

D The field 'name' should be nullable 'String' instead of 'String!'.

💡 Hint

One-to-many means one author has many books.

The 'books' field must be a list to represent many books, so it should be '[Book!]!'.

❓ optimization

advanced

Optimizing nested queries in one-to-many GraphQL relationships

Given a one-to-many relationship between Author and Books, which approach best reduces over-fetching when querying authors with their books?

A Request only the fields needed from both authors and books in the query selection set.

B Always request all fields from authors and books to avoid missing data.

C Use multiple separate queries for authors and books instead of nested queries.

D Request only authors and ignore books to reduce data size.

💡 Hint

GraphQL allows selecting exactly what you want.

Selecting only needed fields avoids fetching unnecessary data, improving performance.

🔧 Debug

expert

Debugging a missing nested list in GraphQL one-to-many query

Why does this query return authors without their books?

query {
  authors {
    name
    books {
      title
    }
  }
}

Schema snippet:

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

A The 'name' field is not requested correctly.

B The query is missing an argument to filter books by author.

C The 'books' field is not a list type; it should be '[Book!]!' to return multiple books.

D The schema is missing the 'Book' type definition.

💡 Hint

Check the type of the 'books' field in the schema.

The 'books' field is defined as a single 'Book' instead of a list, so it returns null or one book, not many.