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

Challenge - 5 Problems

❓ query_result

intermediate

Querying a one-to-one relationship in GraphQL

Given the following GraphQL schema snippet:

type User {
  id: ID!
  name: String!
  profile: Profile
}

type Profile {
  id: ID!
  bio: String
  user: User!
}

What will be the result of this query?

{
  user(id: "1") {
    name
    profile {
      bio
    }
  }
}

A {"data": {"user": null}}

B {"data": {"user": {"name": "Alice", "profile": {"bio": "Loves hiking"}}}}

C {"data": {"user": {"name": "Alice", "profile": null}}}

D SyntaxError: Query missing required fields

💡 Hint

Remember that in a one-to-one relationship, the related object is either present or null.

The query asks for a user with id "1" and their profile's bio. Since the user has a profile, the bio is returned.

🧠 Conceptual

intermediate

Understanding one-to-one relationships in GraphQL

Which statement best describes a one-to-one relationship in GraphQL?

A Each object in type A is linked to exactly one object in type B, and vice versa.

B Each object in type A can be linked to many objects in type B.

C Objects in type A and B are unrelated and cannot reference each other.

D Each object in type A is linked to zero or more objects in type B.

💡 Hint

Think about the meaning of 'one-to-one' in everyday relationships.

One-to-one means each object on one side matches exactly one object on the other side.

📝 Syntax

advanced

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

Find the syntax error in this GraphQL schema snippet defining a one-to-one relationship:

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

type Biography {
  id: ID!
  text: String!
  author: Author
}

A There is no syntax error; the schema is valid.

B The field 'author' in Biography should be non-nullable (Author!).

C The type 'Biography' must have a list of authors, not a single author.

D The field 'biography' in Author should be non-nullable (Biography!).

💡 Hint

Check if the schema syntax follows GraphQL rules for types and fields.

The schema is syntactically valid. Nullability does not cause syntax errors.

❓ optimization

advanced

Optimizing data fetching in one-to-one GraphQL queries

You want to fetch a user and their profile data in one query. Which approach is best to avoid unnecessary data fetching?

A Query only user fields and fetch profile data later with a separate query.

B Query user and profile fields separately in two queries.

C Query user with profile fields nested in the same query.

D Query profile fields only and ignore user fields.

💡 Hint

Think about how GraphQL allows nested queries to reduce round trips.

Querying nested fields in one query reduces network calls and improves performance.

🔧 Debug

expert

Debugging null profile in one-to-one GraphQL query

Given this query:

{
  user(id: "2") {
    name
    profile {
      bio
    }
  }
}

The response is:

{"data": {"user": {"name": "Bob", "profile": null}}}

What is the most likely cause?

A The query syntax is invalid and causes profile to be null.

B The profile field is not defined in the GraphQL schema.

C The user with id "2" does not exist.

D User with id "2" does not have a linked profile in the database.

💡 Hint

Consider what a null nested object means in GraphQL responses.

A null nested object means the relation exists but no linked data is found.