Error types and handling in GraphQL

// Apollo Server error types
const { GraphQLError } = require('graphql');

// Custom error classes
class NotFoundError extends GraphQLError {
  constructor(message) {
    super(message, { extensions: { code: 'NOT_FOUND' } });
  }
}

class ConflictError extends GraphQLError {
  constructor(message) {
    super(message, { extensions: { code: 'CONFLICT' } });
  }
}

// Use in resolvers
const resolvers = {
  Query: {
    user: async (parent, { id }, { db }) => {
      const user = await db.user.findUnique({ where: { id } });
      
      if (!user) {
        throw new NotFoundError(`User with ID ${id} not found`);
      }
      
      return user;
    }
  },
  
  Mutation: {
    createUser: async (parent, { input }, { db }) => {
      // Validation
      if (!input.email.includes('@')) {
        throw new GraphQLError('Invalid email format', {
          extensions: { code: 'BAD_USER_INPUT', field: 'email', value: input.email }
        });
      }
      
      // Check uniqueness
      const existing = await db.user.findUnique({
        where: { email: input.email }
      });
      
      if (existing) {
        throw new ConflictError('Email already in use');
      }
      
      try {
        return await db.user.create({ data: input });
      } catch (error) {
        // Database error
        console.error('Database error:', error);
        throw new GraphQLError('Failed to create user', { extensions: { code: 'DATABASE_ERROR' } });
      }
    }
  }
};