async-graphql/docs/en/src/subscription.md

Subscription

The definition of the subscription root object is slightly different from other root objects. Its resolver function always returns a Stream or Result<Stream>, and the field parameters are usually used as data filtering conditions.

The following example subscribes to an integer stream, which generates one integer per second. The parameter step specifies the integer step size with a default of 1.

# extern crate async_graphql;
# use std::time::Duration;
# use async_graphql::futures_util::stream::Stream;
# use async_graphql::futures_util::StreamExt;
# extern crate tokio_stream;
# extern crate tokio;
use async_graphql::*;

struct Subscription;

#[Subscription]
impl Subscription {
    async fn integers(&self, #[graphql(default = 1)] step: i32) -> impl Stream<Item = i32> {
        let mut value = 0;
        tokio_stream::wrappers::IntervalStream::new(tokio::time::interval(Duration::from_secs(1)))
            .map(move |_| {
                value += step;
                value
            })
    }
}