Depth limiting in GraphQL - Mini Project: Build & Apply

GraphQL Depth Limiting

📖 Scenario: You are building a GraphQL API for a simple blog system. To keep the API safe and fast, you want to limit how deep clients can query nested data.

🎯 Goal: Create a GraphQL schema with types for Author and Post. Then add a depth limit configuration to restrict queries to a maximum depth of 2.

📋 What You'll Learn

Define a GraphQL type Author with fields id (ID), name (String), and posts (list of Post)

Define a GraphQL type Post with fields id (ID), title (String), and content (String)

Create a root Query type with a field authors returning a list of Author

Add a depth limiting configuration that restricts query depth to 2

💡 Why This Matters

🌍 Real World

APIs often need limits on query complexity to avoid slow or expensive requests. Depth limiting helps keep GraphQL APIs safe and fast.

💼 Career

Backend developers and API engineers use depth limiting to protect GraphQL services from abuse and performance issues.

1

Define GraphQL Types

Create GraphQL types Author and Post with the exact fields: Author has id (ID), name (String), and posts (list of Post). Post has id (ID), title (String), and content (String).

GraphQL

# Define GraphQL types Author and Post with specified fields

Need a hint?

Use type keyword to define types. Lists are wrapped in square brackets like [Post].

2

Add Root Query Type

Add a root Query type with a field authors that returns a list of Author.

GraphQL

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

type Post {
  id: ID
  title: String
  content: String
}

# Add Query type with authors field returning [Author]

Need a hint?

The root query type is named Query. Define authors as a list of Author.

3

Set Depth Limit Variable

Create a variable called maxDepth and set it to 2 to limit query depth.

GraphQL

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

type Post {
  id: ID
  title: String
  content: String
}

type Query {
  authors: [Author]
}

# Set maxDepth variable to 2

Need a hint?

Use const maxDepth = 2 to create the depth limit variable.

4

Apply Depth Limiting Middleware

Add a depth limiting middleware configuration using maxDepth to restrict queries to depth 2. Use depthLimit(maxDepth) in your GraphQL server setup.

GraphQL

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

type Post {
  id: ID
  title: String
  content: String
}

type Query {
  authors: [Author]
}

const maxDepth = 2;

# Add depthLimit(maxDepth) middleware in server setup

Need a hint?

Use validationRules: [depthLimit(maxDepth)] in your ApolloServer config to apply depth limiting.