Are subscriptions limited to being top level?

[jerel]

I think this is a bug but I'm not sure... I've spent several days reading code and trying in vain to achieve this so I'd like a second opinion.

Queries can be set up like this (and so can mutations):

pub struct QueryRoot;

#[juniper::graphql_object(Context = Context)]
impl QueryRoot {
  fn settings(&self) -> settings::SettingQueries {
    settings::SettingQueries
  }
  fn other(&self) -> other::OtherQueries {
    other::OtherQueries
  }
}

However, no variation of this seems to be possible with Subscriptions (this doesn't compile):

pub struct SubscriptionRoot;

#[juniper::graphql_subscription(Context = Context)]
impl SubscriptionRoot {
  fn settings(&self) -> settings::SettingSubscriptions {
    settings::SettingSubscriptions
  }
  fn other(&self) -> other::OtherSubscriptions {
    other::OtherSubscriptions
  }
}

Shouldn't this work or is it a design decision? Are all subscriptions for the whole app required to be in one root impl?

[LegNeato]

What is the compilation error you are getting? I didn't work on the subscriptions work but might be able to answer the question.

[jerel]

Thanks @LegNeato, I should have added all this to the original issue. I'll show a couple of the angles that I've tried and their errors:

// this is identical to my usage of the Query/Mutation API but with s/graphql_object/graphql_subscription/ and async fns
pub struct SubscriptionRoot;

#[juniper::graphql_subscription(Context = Context)]
impl SubscriptionRoot {
  async fn settings(&self) -> settings::SettingSubscriptions {
    settings::SettingSubscriptions
  }
  async fn other(&self) -> other::OtherSubscriptions {
    other::OtherSubscriptions
  }
}

pub struct SettingSubscriptions;
#[juniper::graphql_subscription(Context = Context)]
impl SettingSubscriptions {
  pub async fn settings() ...
}

gives this error at the SubscriptionRoot site:

#[juniper::graphql_subscription(Context = Context)]
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `futures::Stream` is not implemented for SettingSubscriptions

So I thought "maybe we can define the top level as a graphql_object which then pulls in the graphql_subscription":

pub struct SubscriptionRoot;

#[juniper::graphql_object(Context = Context)]
impl SubscriptionRoot {
  fn settings(&self) -> settings::SettingSubscriptions {
    settings::SettingSubscriptions
  }
  fn other(&self) -> other::OtherSubscriptions {
    other::OtherSubscriptions
  }
}

pub struct SettingSubscriptions;
#[juniper::graphql_subscription(Context = Context)]
impl SettingSubscriptions {
  pub async fn settings() ...
}

gives this error at the SubscriptionRoot site:

#[juniper::graphql_object(Context = Context)]
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `GraphQLValueAsync<__S>` is not implemented for SettingSubscriptions

Which is understandable I suppose because we're defining SubscriptionRoot as a graphql_object. I thought perhaps this was a way that could work today in userland code but I wasn't able to get GraphQLValueAsync<__S> defined correctly for some reason.

[tyranron]

@jerel as far as I recall, this is not supported at the moment. The reason is that is not clear how such situations should be resolved. A subscription in a nutshell is a Stream. So having a Stream, whcih field resolves to another Stream, how you expect to behave this on client?

Do you have any reference examples how it's handled in other languages?