Gateway composition in GraphQL - Mini Project: Build & Apply

Build a GraphQL Gateway with Schema Composition

📖 Scenario: You are building a GraphQL gateway that combines two separate services: Users and Products. Each service has its own schema. Your gateway will compose these schemas into one unified schema so clients can query both users and products from a single endpoint.

🎯 Goal: Create a GraphQL gateway schema by composing two service schemas: User and Product. You will define the initial schemas, add configuration for schema stitching, compose the schemas, and finalize the gateway schema.

📋 What You'll Learn

Create two GraphQL schemas as strings: userSchema and productSchema with specified types

Add a configuration variable gatewayConfig to hold schema stitching options

Compose the two schemas into one unified schema using makeExecutableSchema and mergeSchemas

Export the final composed schema as gatewaySchema

💡 Why This Matters

🌍 Real World

GraphQL gateway composition is used in microservice architectures to combine multiple GraphQL APIs into a single endpoint for clients.

💼 Career

Understanding schema composition is essential for backend developers working with GraphQL in distributed systems and API gateways.

1

Define User and Product schemas

Create two GraphQL schema strings called userSchema and productSchema. userSchema should define a User type with fields id: ID! and name: String!. productSchema should define a Product type with fields id: ID! and title: String!.

GraphQL

# Define userSchema and productSchema as GraphQL schema strings
# Your code here

Need a hint?

Define userSchema and productSchema as template strings with the exact type definitions.

2

Add gateway configuration for schema stitching

Create a configuration object called gatewayConfig with a property schemas that is an array containing userSchema and productSchema.

GraphQL

const userSchema = `
  type User {
    id: ID!
    name: String!
  }
  type Query {
    users: [User]
  }
`;

const productSchema = `
  type Product {
    id: ID!
    title: String!
  }
  type Query {
    products: [Product]
  }
`;

// Create gatewayConfig with schemas array
# Your code here

Need a hint?

Define gatewayConfig as an object with a schemas property that holds both schema strings.

3

Compose schemas into one executable schema

Use makeExecutableSchema from @graphql-tools/schema to create executable schemas from userSchema and productSchema. Then use mergeSchemas from @graphql-tools/merge to combine them into one schema. Assign the result to a variable called composedSchema.

GraphQL

const userSchema = `
  type User {
    id: ID!
    name: String!
  }
  type Query {
    users: [User]
  }
`;

const productSchema = `
  type Product {
    id: ID!
    title: String!
  }
  type Query {
    products: [Product]
  }
`;

const gatewayConfig = {
  schemas: [userSchema, productSchema]
};

import { makeExecutableSchema } from '@graphql-tools/schema';
import { mergeSchemas } from '@graphql-tools/merge';

// Compose schemas here
# Your code here

Need a hint?

Create executable schemas from the schema strings, then merge them into one schema.

4

Export the final gateway schema

Export the composed schema by assigning composedSchema to a constant called gatewaySchema and export it as the default export.

GraphQL

const userSchema = `
  type User {
    id: ID!
    name: String!
  }
  type Query {
    users: [User]
  }
`;

const productSchema = `
  type Product {
    id: ID!
    title: String!
  }
  type Query {
    products: [Product]
  }
`;

const gatewayConfig = {
  schemas: [userSchema, productSchema]
};

import { makeExecutableSchema } from '@graphql-tools/schema';
import { mergeSchemas } from '@graphql-tools/merge';

const executableUserSchema = makeExecutableSchema({ typeDefs: userSchema });
const executableProductSchema = makeExecutableSchema({ typeDefs: productSchema });

const composedSchema = mergeSchemas({
  schemas: [executableUserSchema, executableProductSchema]
});

// Export gatewaySchema here
# Your code here

Need a hint?

Assign composedSchema to gatewaySchema and export it as default.