Field-level cost analysis in GraphQL - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

Calculate total cost for selected fields

Given a GraphQL query requesting name and price fields of products, and a cost model where name costs 1 unit and price costs 3 units per item, what is the total cost for 5 products?

GraphQL

query {
  products {
    name
    price
  }
}

A 20

B 15

C 10

D 25

💡 Hint

Multiply the cost per field by the number of products and sum.

Each product requests two fields: name (1 unit) and price (3 units). Total per product is 4 units. For 5 products, total cost is 4 * 5 = 20 units.

🧠 Conceptual

intermediate

Understanding cost impact of nested fields

In a GraphQL query, a user has a nested posts field. If user fields cost 2 units each and posts fields cost 1 unit each, which factor most increases total cost?

A Increasing number of users queried

B Increasing number of <code>user</code> fields requested

C Increasing number of posts per user

D Increasing number of <code>posts</code> fields requested

💡 Hint

Think about how nested lists multiply cost.

More posts per user multiply the cost of posts fields by the number of posts, increasing total cost significantly.

📝 Syntax

advanced

Identify syntax error in cost directive usage

Which option contains a syntax error in applying a cost directive to a GraphQL field?

GraphQL

type Query {
  products: [Product] @cost(multipliers: ["first"])
}

type Product {
  name: String @cost(value: 1)
  price: Float @cost(value: 2)
}

A Using @cost(value=1) on <code>price</code> field

B Using @cost(multipliers: ["first"]) on <code>products</code> field

C Using @cost(value: 1) on <code>name</code> field

D Using @cost(value: 2) on <code>price</code> field

💡 Hint

Check the syntax for directive arguments in GraphQL.

GraphQL directive arguments use colon :, not equals =. Option A uses =, causing syntax error.

❓ optimization

advanced

Optimize query cost by reducing field requests

You have a query requesting id, name, description, and price fields for 10 products. Costs per field are: id = 1, name = 2, description = 5, price = 3. Which option reduces total cost the most while keeping id and price?

A Remove <code>name</code> only

B Remove <code>name</code> and <code>description</code>

C Remove <code>price</code> only

D Remove <code>description</code> only

💡 Hint

Calculate cost savings for each removal.

Removing name and description saves (2 + 5) * 10 = 70 units, more than removing name only (20 units) or description only (50 units). Removing price is not allowed.

🔧 Debug

expert

Diagnose unexpected high cost in nested query

A query requests users with nested posts and comments. Each user has 3 posts, each post has 4 comments. Costs: user fields = 2 units each, post fields = 1 unit each, comment fields = 0.5 units each. The query requests 2 fields per user, 3 fields per post, and 2 fields per comment. Why is the total cost unexpectedly high?

A The query requests too many user fields

B The number of users queried is higher than expected

C The cost per comment field is set too low

D The cost calculation multiplies fields by number of comments incorrectly

💡 Hint

Consider how nested lists multiply total cost.

The total cost multiplies the number of fields by the count of nested items. With 3 posts per user and 4 comments per post, the comment fields multiply by 3 * 4 = 12 per user, increasing cost significantly.