Subscription enhancements request

[nirinchev]

To provide a nicer subscribe/unsubscribe API in the GraphQL service, we need the following enhancements to the subscription functionality in realm-js:

• Ability to unsubscribe by name. There should be no reason to subscribe to something only to later unsubscribe.
• Ability to list all active subscriptions. We already have that information in the partial Realm, so there should be no reason not to expose it. I need just the name and the query and not a reference to the subscription instances or anything like that.
• A nicer wrapper around waiting for subscription - something like:

return new Promise((resolve, reject) => {
  const listener = (__, state) => {
    switch (state) {
      case Realm.Sync.SubscriptionState.Complete:
        subscription.removeListener(listener);
        resolve();
        break;
      case Realm.Sync.SubscriptionState.Error:
        subscription.removeListener(listener);
        reject(subscription.error);
        break;
    }
  };
  subscription.addListener(listener);
});

[cmelchior]

Ability to list all active subscriptions. We already have that information in the partial Realm, so there should be no reason not to expose it. I need just the name and the query and not a reference to the subscription instances or anything like that.

IMO we should just expose the __ResultSet as a Subscription. I suspect that trying to do anything else is going to bite us later.

[nirinchev]

I'm not against that, but if we decide to do that, we should enhance the Subscription interface and add properties for the name and the serialized query. Otherwise it's fairly useless to get a list of these.

[cmelchior]

Yup. For bindings that support the text-based parser, they could also enable directly returning the Results object.

Java is currently a bit hampered in that regard, but just exposing a text-based description + name seems fine for a first iteration.