Cursor connections

Relay's cursor connection specification is designed to provide a consistent method for query paging. For more details on the specification see the GraphQL Cursor Connections Specification。

Defining a cursor connection in async-graphql is very simple, you just call the connection::query function and query data in the closure.

#![allow(unused)]
fn main() {
extern crate async_graphql;
use async_graphql::*;
use async_graphql::types::connection::*;

struct Query;

#[Object]
impl Query {
    async fn numbers(&self,
        after: Option<String>,
        before: Option<String>,
        first: Option<i32>,
        last: Option<i32>,
    ) -> Result<Connection<usize, i32, EmptyFields, EmptyFields>> {
        query(after, before, first, last, |after, before, first, last| async move {
            let mut start = after.map(|after| after + 1).unwrap_or(0);
            let mut end = before.unwrap_or(10000);
            if let Some(first) = first {
                end = (start + first).min(end);
            }
            if let Some(last) = last {
                start = if last > end - start {
                     end
                } else {
                    end - last
                };
            }
            let mut connection = Connection::new(start > 0, end < 10000);
            connection.edges.extend(
                (start..end).into_iter().map(|n|
                    Edge::with_additional_fields(n, n as i32, EmptyFields)
            ));
            Ok::<_, async_graphql::Error>(connection)
        }).await
    }
}

}