Basic query syntax in GraphQL - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What is the output of this GraphQL query?

Given the following GraphQL schema for a blog:

type Query {
  posts: [Post]
}

type Post {
  id: ID
  title: String
  author: Author
}

type Author {
  id: ID
  name: String
}

And the data:

{
  posts: [
    { id: "1", title: "Hello World", author: { id: "a1", name: "Alice" } },
    { id: "2", title: "GraphQL Basics", author: { id: "a2", name: "Bob" } }
  ]
}

What will be the result of this query?

{
  posts {
    title
    author {
      name
    }
  }
}

GraphQL

{
  posts {
    title
    author {
      name
    }
  }
}

A {"data":{"posts":[{"id":"1","title":"Hello World"},{"id":"2","title":"GraphQL Basics"}]}}

B {"data":{"posts":[{"title":"Hello World"},{"title":"GraphQL Basics"}]}}

C {"data":{"posts":[{"title":"Hello World","author":{"name":"Alice"}},{"title":"GraphQL Basics","author":{"name":"Bob"}}]}}

D {"errors":[{"message":"Field 'author' not found on type 'Post'"}]}

💡 Hint

Look at the fields requested in the query and match them with the schema.

The query requests title and nested author { name } for each post. The data includes these fields, so the response includes them accordingly.

🧠 Conceptual

intermediate

Which part of a GraphQL query specifies what data to return?

In GraphQL, what is the name of the section inside the curly braces that tells the server what fields to fetch?

A Selection set

B Mutation

C Subscription

D Directive

💡 Hint

It is the list of fields inside the braces after the query keyword.

The selection set is the part of the query inside curly braces that specifies which fields to retrieve.

📝 Syntax

advanced

What error does this GraphQL query produce?

Consider this query:

{
  posts(
    title: "Hello World"
  ) {
    id
    title
  }
}

What error will this cause?

GraphQL

{
  posts(
    title: "Hello World"
  ) {
    id
    title
  }
}

A Validation Error: Field 'posts' does not accept arguments

B Syntax Error: Arguments must be inside parentheses after the field name

C Runtime Error: Cannot query field 'title' on type 'Post'

D No error, query runs successfully

💡 Hint

Check if the schema allows arguments on the 'posts' field.

The 'posts' field in the schema does not accept any arguments, so providing one causes a validation error.

❓ optimization

advanced

Which query is more efficient to fetch only post titles?

You want to get only the titles of all posts. Which query is better for performance?

A { posts { id title author { name } } }

B { posts { id } }

C { posts { title author { id } } }

D { posts { title } }

💡 Hint

Request only the fields you need to reduce data transfer.

Query A requests only the 'title' field, minimizing data fetched and improving performance.

🔧 Debug

expert

Why does this GraphQL query fail?

Given the schema:

type Query {
  post(id: ID!): Post
}

type Post {
  id: ID
  title: String
}

And this query:

{
  post {
    id
    title
  }
}

Why does it fail?

GraphQL

{
  post {
    id
    title
  }
}

A Error: Cannot query field 'title' on type 'Query'

B Error: Missing required argument 'id' for field 'post'

C No error, query runs successfully

D Error: Field 'post' does not exist on type 'Query'

💡 Hint

Check if the 'post' field requires any arguments.

The 'post' field requires an 'id' argument, which is missing in the query, causing an error.