GraphQL Directive example

directives.ts

import { SchemaDirectiveVisitor } from 'graphql-tools';
import { defaultFieldResolver, GraphQLField, GraphQLResolveInfo } from 'graphql';
import { ForbiddenError } from '../errors';
import { ContextParameters } from 'graphql-yoga/dist/types';

// Throws an error if the query requested a field that is marked by this directive
// and the requested user is not the authenticated user.
export default class OwnerDirective extends SchemaDirectiveVisitor {
  visitFieldDefinition(field: GraphQLField<any, any>) {
    this.checkIfOwner(field);
  }

  checkIfOwner(field: GraphQLField<any, any>) {
    const { resolve = defaultFieldResolver } = field;
    field.resolve = async function(
      parent: any,
      args: any,
      context: ContextParameters & { currentUser: any },
      info: GraphQLResolveInfo
    ) {
      if (context.currentUser.id !== info.variableValues.userId) {
        throw new ForbiddenError();
      }
      return resolve.call(this, parent, args, context, info);
    };
  }
}