Why is my resolver returning null even though my database has data?

Check that your resolver path matches your schema exactly—GraphQL is case-sensitive. Also verify that your resolver is returning the data (not just fetching it) and that any async resolvers use await or return the Promise.

How do I debug the N+1 problem in my GraphQL server?

Enable Apollo Server's tracing feature or add logging to your resolvers to see how many database queries execute per request. If you see repeated queries for the same type of data, implement DataLoader to batch those requests.

Why are my subscriptions not working in production?

The in-memory PubSub class doesn't share events across server instances. If you're running multiple instances (or Render replaces your instance during deploys), subscribers on one instance won't receive events published on another. Use a Redis-backed PubSub adapter instead.

How do I handle authentication errors in GraphQL?

Throw errors with descriptive codes from your resolvers. Use GraphQLError with an extensions object containing an error code like UNAUTHENTICATED or FORBIDDEN. Clients can then check this code to handle different error types appropriately.

Why does a null field cause my entire query to fail?

Non-nullable fields (marked with !) propagate null upward when they can't be resolved. If a non-nullable field returns null, GraphQL nullifies its parent object, which can cascade up the tree. Review your schema and only mark fields as non-nullable when you can guarantee their presence.

How do I prevent malicious or expensive queries?

Implement query complexity analysis using libraries like graphql-query-complexity. Assign costs to fields based on their computational expense, set a maximum allowed complexity per query, and reject queries that exceed the limit.

Can I use GraphQL with my existing REST API?

Yes. Your GraphQL resolvers can fetch data from any source, including REST endpoints. This approach lets you introduce GraphQL incrementally without rewriting your backend. Use DataLoader to batch and cache REST calls for better performance.

services

How to build and deploy a GraphQL API

January 16, 2026

Tired of building APIs that force clients to request more data than they need, or chasing multiple endpoints to get what they want? GraphQL changes that game entirely. Instead of organizing your API around multiple endpoints that return fixed data structures, GraphQL centers everything around a strongly-typed schema where clients specify exactly what data they need. This article walks you through the main steps of building a GraphQL server, focusing on the patterns and architectural decisions that distinguish GraphQL from traditional REST approaches.

Prerequisites

Before starting, ensure you have:

Node.js 18+ installed (check with node --version)
npm or yarn package manager
Basic JavaScript knowledge: async/await, destructuring, arrow functions
Basic API concepts: HTTP methods, request/response cycles

GraphQL fundamentals and server setup

Your GraphQL server performs three core operations: it receives queries from clients, validates those queries against your schema definition, and executes resolver functions to fetch the requested data. Unlike REST servers that map URLs to handler functions, GraphQL servers have a single endpoint that processes different queries based on the schema.

Apollo Server offers extensive tooling and production-ready defaults, while GraphQL Yoga provides a lighter-weight, more flexible foundation. Choose Apollo Server for comprehensive features, choose GraphQL Yoga for fine-grained control.

javascript

import { ApolloServer } from '@apollo/server';
import { startStandaloneServer } from '@apollo/server/standalone';

// Schema defines your API's capabilities
const typeDefs = `#graphql
  type Query {
    hello: String
  }
`;

// Resolvers fetch the actual data
const resolvers = {
  Query: {
    hello: () => 'Hello from GraphQL!'
  }
};

const server = new ApolloServer({ typeDefs, resolvers });
const { url } = await startStandaloneServer(server, { listen: { port: 4000 } });
console.log(`Server ready at ${url}`);

For production, add environment-based configuration, CORS configuration for browser clients, request validation middleware, and proper error handling. Apollo Server’s documentation covers these requirements in detail.

Schema design patterns

Your schema serves as a contract between your server and clients, written in GraphQL's Schema Definition Language (SDL). This contract enables powerful developer tooling—editors can autocomplete queries, validate them before execution, and generate TypeScript types automatically.

GraphQL organizes operations into three root types: Query for read operations, Mutation for write operations that modify server state, and Subscription for real-time updates over WebSocket connections.

Field nullability has significant implications. A field marked with ! (non-nullable) represents a guarantee—if the resolver can't provide that value, the entire parent object becomes null. This cascading behavior means you should only mark fields non-nullable when you can guarantee their presence.

graphql

# Read operations - should be idempotent
type Query {
  user(id: ID!): User
  posts(limit: Int, offset: Int): [Post!]!
}

# Write operations that modify data
type Mutation {
  createPost(input: CreatePostInput!): Post
  updateUser(id: ID!, input: UpdateUserInput!): User
}

type User {
  id: ID!  # Non-nullable - GraphQL guarantees this field
  username: String!
  email: String!
  posts: [Post!]!
}

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

# Input types group mutation parameters
input CreatePostInput {
  title: String!
  content: String!
  authorId: ID!
}

input UpdateUserInput {
  username: String
  email: String
}

Real schemas require additional validation rules, pagination strategies, and careful consideration of relationships between types. The @deprecated directive helps you evolve schemas without breaking existing clients.

Building resolvers and data fetching

Resolvers are functions that populate data for fields in your schema. GraphQL executes resolvers hierarchically—a parent resolver runs first, then child field resolvers receive the parent's return value as their first argument.

Each resolver receives four arguments: parent (data from the parent resolver), args (field arguments), context (shared data like database connections and authentication state), and info (query metadata). GraphQL creates the context object once per request and passes it to all resolvers.

javascript

const resolvers = {
  Query: {
    user: async (parent, { id }, context) => {
      return context.db.users.findById(id);
    }
  },
  User: {
    // Parent is the User object from Query.user resolver
    posts: async (parent, args, context) => {
      return context.db.posts.findByAuthorId(parent.id);
    }
  },
  Mutation: {
    createPost: async (parent, { input }, context) => {
      if (!context.user) throw new Error('Not authenticated');
      return context.db.posts.create(input);
    }
  }
};

Production resolvers require input validation using libraries like Joi or Zod, proper error handling, and authorization checks. Consider implementing field-level authorization using GraphQL Shield.

Solving the N+1 query problem

GraphQL's resolver architecture makes the N+1 problem particularly visible. When a query requests a list of objects and a related field for each, naive resolvers execute one query for the list plus one query per item for the related field.

DataLoader solves this by batching and caching data fetches within a single request. It collects all IDs requested during a single tick of the event loop, makes one batched request, and distributes results to the waiting resolvers.

javascript

import DataLoader from 'dataloader';

const createPostLoader = (db) => new DataLoader(async (authorIds) => {
  const posts = await db.posts.findByAuthorIds(authorIds);
  return authorIds.map(id => posts.filter(post => post.authorId === id));
});

// Create loaders per request in context
const context = ({ req }) => ({
  user: req.user,
  loaders: {
    posts: createPostLoader(db)
  }
});

// Use in resolvers
const resolvers = {
  User: {
    posts: (parent, args, context) => {
      return context.loaders.posts.load(parent.id);
    }
  }
};

Consider query complexity analysis using graphql-query-complexity to prevent resource exhaustion from deeply nested queries.

Authentication and authorization

Authentication in GraphQL happens at the context level because there's typically one endpoint. You'll extract authentication tokens from request headers, validate them, and attach user information to the context object.

javascript

const context = async ({ req }) => {
  const token = req.headers.authorization?.replace('Bearer ', '');
  
  let user = null;
  if (token) {
    try {
      user = await validateTokenAndGetUser(token);
    } catch (err) {
      console.error('Token validation failed:', err);
    }
  }
  
  return { user, db };
};

const resolvers = {
  Mutation: {
    deletePost: (parent, { id }, context) => {
      if (!context.user) {
        throw new Error('Authentication required');
      }
      return context.db.posts.delete(id);
    }
  }
};

Production systems need robust JWT validation, token refresh mechanisms, rate limiting, and comprehensive audit logging. Consider using express-jwt for middleware integration.

Real-time features with subscriptions

Subscriptions enable real-time updates by maintaining WebSocket connections. Clients subscribe to specific events, and your server pushes updates when those events occur.

javascript

import { PubSub } from 'graphql-subscriptions';

const pubsub = new PubSub();

const typeDefs = `#graphql
  type Subscription {
    postCreated: Post
  }
`;

const resolvers = {
  Mutation: {
    createPost: async (parent, { input }, context) => {
      const post = await context.db.posts.create(input);
      pubsub.publish('POST_CREATED', { postCreated: post });
      return post;
    }
  },
  Subscription: {
    postCreated: {
      subscribe: () => pubsub.asyncIterator(['POST_CREATED'])
    }
  }
};

The PubSub class from graphql-subscriptions stores subscriptions in memory, which means events published on one server instance won't reach subscribers connected to a different instance. This becomes a problem when you scale horizontally or when Render replaces instances during deploys. For production, use graphql-redis-subscriptions or a similar adapter that shares events across all instances through an external message broker.

Deployment considerations

Deploying GraphQL services requires attention to schema validation, query complexity limits, and persistent connection handling.

When deploying to Render, configure health checks appropriately. Your GraphQL server should expose a health check endpoint separate from the main GraphQL endpoint. This allows Render to verify your service is functioning normally during zero-downtime deploys. You can configure environment variables through the Render Dashboard.

For WebSocket-based subscriptions, Render's Web Services support WebSocket connections. Note that WebSocket connections close automatically when an instance shuts down (such as during a deploy). Implement reconnection logic in your clients to handle these interruptions gracefully. Your application should handle connection lifecycle appropriately, as Render doesn't impose a fixed timeout but connections will close when instances are replaced.

javascript

const loggingPlugin = {
  async requestDidStart({ request }) {
    const start = Date.now();
    return {
      async willSendResponse({ response }) {
        const duration = Date.now() - start;
        console.log({
          query: request.query,
          duration,
          errors: response.errors?.length || 0
        });
      }
    };
  }
};

const server = new ApolloServer({
  typeDefs,
  resolvers,
  plugins: [loggingPlugin]
});

Common troubleshooting patterns

Resolver not executing: Verify the resolver path matches your schema exactly—GraphQL is case-sensitive.
Null propagation errors: When non-nullable fields return null, GraphQL nullifies the entire parent object. Review your schema's nullability annotations.
Context not available: The context factory must return an object—ensure your server framework supports async context functions.
Performance degradation: Profile resolver execution times and check for N+1 patterns. Enable Apollo Server's tracing to identify slow resolvers.

Next steps

To deepen your knowledge:

Implement cursor-based pagination using the Relay connection specification
Add persisted queries to improve security and performance
Explore federation with Apollo Federation for splitting large schemas across services
Study query cost analysis algorithms to prevent resource exhaustion

GraphQL's type system and resolver pattern provide powerful abstractions for building flexible APIs. You now have the foundational knowledge to build production-ready GraphQL services. The patterns you've learned here scale from simple hobby projects to complex systems serving millions of requests.

Prerequisites

GraphQL fundamentals and server setup

Schema design patterns

Building resolvers and data fetching

Solving the N+1 query problem

Authentication and authorization

Real-time features with subscriptions

Deployment considerations

Common troubleshooting patterns

Next steps

FAQs

Why is my resolver returning null even though my database has data?

How do I debug the N+1 problem in my GraphQL server?

Why are my subscriptions not working in production?

How do I handle authentication errors in GraphQL?

Why does a null field cause my entire query to fail?

How do I prevent malicious or expensive queries?

Can I use GraphQL with my existing REST API?