Nested field queries in GraphQL - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What is the output of this nested GraphQL query?

Given the following GraphQL schema snippet:

type Author {
  id: ID!
  name: String!
  posts: [Post!]!
}

type Post {
  id: ID!
  title: String!
  comments: [Comment!]!
}

type Comment {
  id: ID!
  content: String!
}

And the query:

{
  author(id: "1") {
    name
    posts {
      title
      comments {
        content
      }
    }
  }
}

Assuming the author with id "1" has 1 post titled "Hello World" with 2 comments "Nice post!" and "Thanks for sharing", what is the expected JSON output?

GraphQL

{
  author(id: "1") {
    name
    posts {
      title
      comments {
        content
      }
    }
  }
}

A {"data":{"author":{"name":"Alice","posts":[{"title":"Hello World"}]}}}

B {"data":{"author":{"name":"Alice","posts":[{"title":"Hello World","comments":[{"content":"Thanks for sharing"}]}]}}}

C {"data":{"author":{"name":"Alice","posts":[{"title":"Hello World","comments":[{"content":"Nice post!"},{"content":"Thanks for sharing"}]}]}}}

D {"data":{"author":{"name":"Alice","posts":[]}}}

💡 Hint

Remember that nested fields return all requested subfields for each item.

The query requests the author's name, their posts, and for each post, the comments with their content. Since the author has one post with two comments, all are included in the output.

📝 Syntax

intermediate

Which GraphQL query syntax is correct for nested fields?

Choose the syntactically valid GraphQL query to fetch an author's name and the titles of their posts.

A { author(id: "1") { name, posts { title } } }

B { author(id: "1") { name posts { title } } }

C { author(id: "1") { name; posts { title } } }

D { author(id: "1") { name posts: { title } } }

💡 Hint

GraphQL queries do not use commas or semicolons between fields.

GraphQL syntax requires fields to be listed without commas or semicolons. Option B correctly lists fields with spaces only.

❓ optimization

advanced

How to optimize a nested GraphQL query to reduce data size?

Given a query fetching authors with their posts and comments, which modification reduces the data size returned?

{
  authors {
    id
    name
    posts {
      id
      title
      comments {
        id
        content
      }
    }
  }
}

A Fetch only comment ids, not content.

B Remove fetching comments field entirely.

C Fetch only author names without posts.

D Fetch posts without ids.

💡 Hint

Consider which fields are necessary for your use case to minimize data transfer.

Fetching only comment ids reduces data size while still identifying comments. Removing comments entirely or posts may lose needed info. Omitting post ids may cause issues if ids are needed.

🔧 Debug

advanced

Why does this nested GraphQL query return null for posts?

Given the query:

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

The response is:

{
  "data": {
    "author": {
      "name": "Bob",
      "posts": null
    }
  }
}

What is the most likely cause?

A Posts field is misspelled in the query.

B Syntax error in the query causing posts to be null.

C Server does not support nested queries.

D Author with id "2" has no posts and posts field is nullable.

💡 Hint

Null in nested fields often means no data or nullable field.

The posts field is nullable and the author has no posts, so the server returns null for posts instead of an empty list.

🧠 Conceptual

expert

What is the main benefit of nested field queries in GraphQL?

Choose the best explanation for why nested field queries are useful in GraphQL.

A They allow fetching related data in a single request, reducing multiple round-trips.

B They enforce strict schema validation on the server side.

C They automatically cache all nested data on the client.

D They prevent any data from being fetched unless explicitly authorized.

💡 Hint

Think about how nested queries affect network requests.

Nested queries let clients request related data in one go, avoiding multiple separate requests and improving efficiency.