Subgraph definition in GraphQL - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What is the output of this subgraph query?

Given this subgraph schema and query, what will be the result?

type Product @entity {
  id: ID!
  name: String!
  price: Int!
}

query {
  products {
    id
    name
  }
}

GraphQL

schema {
  query: Query
}

type Query {
  products: [Product!]!
}

type Product @entity {
  id: ID!
  name: String!
  price: Int!
}

query {
  products {
    id
    name
  }
}

A [{"id": "1", "name": "Apple"}, {"id": "2", "name": "Banana"}]

B [{"id": "1", "name": "Apple", "price": 100}, {"id": "2", "name": "Banana", "price": 50}]

C [{"id": "1"}, {"id": "2"}]

D []

💡 Hint

The query only asks for id and name, so price is not included in the output.

The query requests only id and name fields for each product. The subgraph returns all products with those fields. The price field is not requested, so it is not in the output.

📝 Syntax

intermediate

Which option contains a syntax error in subgraph definition?

Identify the option that has a syntax error in the GraphQL subgraph schema definition.

GraphQL

type User @entity {
  id: ID!
  username: String!
  email: String!
}

A

type User @entity {
  id: ID!
  username: String!
  email: String!
}

B

type User @entity {
  id: ID!
  username: String!
  email: String
}

C

type User @entity {
  id: ID!
  username: String!
  email: String!

D

type User @entity {
  id: ID!
  username: String!
  email: String!
  age: Int
}

💡 Hint

Check for missing closing braces or punctuation.

Option C is missing the closing brace '}' at the end of the type definition, causing a syntax error.

❓ optimization

advanced

Which subgraph query is optimized to fetch only needed data?

You want to fetch only the id and title of posts from a subgraph. Which query is optimized?

GraphQL

type Post @entity {
  id: ID!
  title: String!
  content: String!
  author: User!
}

A

query {
  posts {
    id
  }
}

B

query {
  posts {
    id
    title
    content
  }
}

C

query {
  posts {
    id
    author {
      id
    }
  }
}

D

query {
  posts {
    id
    title
  }
}

💡 Hint

Only request the fields you need to reduce data transfer.

Option D requests only id and title, exactly what is needed. Other options request extra fields, making them less optimized.

🔧 Debug

advanced

Why does this subgraph query return an empty list?

Given this subgraph schema and query, why does the query return an empty list?

type Book @entity {
  id: ID!
  title: String!
  author: String!
}

query {
  books(where: {author: "Unknown"}) {
    id
    title
  }
}

GraphQL

type Book @entity {
  id: ID!
  title: String!
  author: String!
}

query {
  books(where: {author: "Unknown"}) {
    id
    title
  }
}

A The query is missing the 'id' field, so no results are returned.

B There are no books with author exactly "Unknown" in the data.

C The 'author' field is not indexed, so filtering is not supported.

D The 'where' filter syntax is invalid and causes the query to fail silently.

💡 Hint

Check if the data contains any matching entries for the filter.

The query returns an empty list because no book has the author field exactly equal to "Unknown". The filter is valid and the query runs correctly.

🧠 Conceptual

expert

What is the main purpose of a subgraph in a GraphQL architecture?

Choose the best explanation for the role of a subgraph in a GraphQL system.

A A subgraph defines a part of the overall schema and data, allowing modular and scalable GraphQL services.

B A subgraph is a client-side cache that stores query results for faster access.

C A subgraph is a database table that stores GraphQL queries and mutations.

D A subgraph is a tool to convert REST APIs into GraphQL automatically.

💡 Hint

Think about how large GraphQL schemas are managed in parts.

A subgraph is a modular piece of the overall GraphQL schema and data, enabling teams to develop and deploy parts of the graph independently. It is not a cache, database table, or conversion tool.