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

Challenge - 5 Problems

❓ query_result

intermediate

Querying many-to-many relationships with GraphQL

Given a GraphQL schema where Students and Courses have a many-to-many relationship through enrollments, what is the expected output of this query?

query {
  students {
    name
    courses {
      title
    }
  }
}

Assume the data has one student named "Alice" enrolled in "Math" and "Science" courses.

A [{"name": "Alice", "courses": [{"title": "Math"}]}]

B [{"name": "Alice", "courses": [{"title": "Math"}, {"title": "Science"}]}]

C [{"name": "Alice"}]

D []

💡 Hint

Think about how many courses Alice is enrolled in and how GraphQL returns nested objects.

The query fetches all students with their enrolled courses. Since Alice is enrolled in both Math and Science, both courses appear nested under her name.

🧠 Conceptual

intermediate

Understanding many-to-many relationship tables

In a many-to-many relationship between Authors and Books, which table correctly represents the join table?

A A table named <em>author_books</em> with columns <code>author_id</code> and <code>book_id</code>.

B A table named <em>books</em> with columns <code>author_name</code> and <code>book_title</code>.

C A table named <em>authors</em> with columns <code>author_name</code> and <code>book_title</code>.

D A table named <em>author_book_titles</em> with columns <code>author_name</code> and <code>book_title</code>.

💡 Hint

Think about how many-to-many relationships are stored using IDs in a separate table.

The join table stores pairs of IDs from both tables to link authors and books without duplicating data.

📝 Syntax

advanced

Correct GraphQL schema for many-to-many

Which GraphQL type definition correctly models a many-to-many relationship between Users and Groups?

A type User { id: ID! groups: Group } type Group { id: ID! users: User }

B type User { id: ID! group: Group } type Group { id: ID! user: User }

C type User { id: ID! groups: [Group!]! } type Group { id: ID! users: [User!]! }

D type User { id: ID! groups: Group! } type Group { id: ID! users: User! }

💡 Hint

Remember that many-to-many means lists on both sides.

Option C uses lists of non-nullable Group and User types on both sides, correctly modeling many-to-many.

❓ optimization

advanced

Optimizing many-to-many GraphQL queries

To reduce database load when querying many-to-many relationships in GraphQL, which approach is best?

A Avoid using GraphQL and switch to REST API.

B Query each related entity separately without batching.

C Fetch all data in one big query without filtering.

D Use DataLoader to batch and cache database requests for related entities.

💡 Hint

Think about how to avoid repeated database calls for the same data.

DataLoader batches and caches requests, reducing duplicate queries and improving performance.

🔧 Debug

expert

Debugging missing data in many-to-many GraphQL query

A GraphQL query for users and their groups returns users but the groups field is always empty. The schema is correct. What is the most likely cause?

A The resolver for the <code>groups</code> field is missing or returns an empty list.

B The database has no users stored.

C The GraphQL query syntax is invalid.

D The <code>users</code> field is not defined in the schema.

💡 Hint

Check the resolver functions for nested fields.

If the groups field resolver is missing or returns empty, the query returns empty groups even if users exist.