Subscribing fields to types

Gato GraphQL uses the Publish-subscribe pattern to have fields be "subscribed" to types, in which a FieldResolver entity has fields add to some TypeResolver entity.

In this example, class UserFieldResolver adds fields username, email and url to class UserTypeResolver, which resolves type User:

class UserFieldResolver extends AbstractDBDataFieldResolver
{
  public static function getClassesToAttachTo(): array
  {
    return [UserTypeResolver::class];
  }
 
  public static function getFieldNamesToResolve(): array
  {
    return [
      'username',
      'email',
      'url',
    ];
  }Copy

The User type does not know in advance which fields it will satisfy, but these (username, email and url) are instead injected to the type by the field resolver.

This way, the GraphQL schema becomes easily extensible: by simply adding a field resolver, any extension can add new fields to an existing type (such as field User.shippingAddress), or override how a field is resolved (such as redefining User.url to return the user's website instead).