Add doc

src/types/connection/stream.rs

@@ -1,8 +1,62 @@
 use crate::types::connection::{EmptyEdgeFields, QueryOperation};
 use crate::{Connection, Context, Cursor, DataSource, FieldResult, ObjectType};
 use futures::{Stream, StreamExt};
+use std::collections::VecDeque;
 use std::pin::Pin;
 
+/// Utility struct to convert a Stream to a Connection
+///
+/// # Examples
+///
+/// ```rust
+/// use async_graphql::*;
+/// use byteorder::{ReadBytesExt, BE};
+/// use futures::StreamExt;
+///
+/// struct QueryRoot;
+///
+/// #[Object]
+/// impl QueryRoot {
+///     async fn stream_connection(&self, ctx: &Context<'_>,
+///         after: Option<Cursor>,
+///         before: Option<Cursor>,
+///         first: Option<i32>,
+///         last: Option<i32>
+///     ) -> FieldResult<Connection<&str>> {
+///         let edges_stream = futures::stream::iter(vec!["a", "b", "c", "d", "e", "f"])
+///             .map(|node| {
+///                 let cursor: Cursor = node.to_owned().into();
+///                 (cursor, EmptyEdgeFields, node)
+///             });
+///
+///         let mut source: StreamDataSource<_> = edges_stream.into();
+///         source.query(ctx, after, before, first, last).await
+///     }
+/// }
+///
+/// #[async_std::main]
+/// async fn main() {
+///     let schema = Schema::new(QueryRoot, EmptyMutation, EmptySubscription);
+///
+///     assert_eq!(schema.execute("{ streamConnection(first: 2) { edges { node } } }").await.unwrap().data, serde_json::json!({
+///         "streamConnection": {
+///             "edges": [
+///                 { "node": "a" },
+///                 { "node": "b" }
+///             ]
+///         },
+///     }));
+///
+///     assert_eq!(schema.execute("{ streamConnection(last: 2) { edges { node } } }").await.unwrap().data, serde_json::json!({
+///         "streamConnection": {
+///             "edges": [
+///                 { "node": "e" },
+///                 { "node": "f" }
+///             ]
+///         },
+///     }));
+/// }
+/// ```
 pub struct StreamDataSource<'a, T, E = EmptyEdgeFields>
 where
     T: Send + Sync + 'a,
@@ -11,7 +65,21 @@ where
     stream: Pin<Box<dyn Stream<Item = (Cursor, E, T)> + Send + Sync + 'a>>,
 }
 
-impl<'a, S, T, E> From<S> for StreamDataSource<'a, T, E>
+impl<'a, T, E> StreamDataSource<'a, T, E>
+where
+    T: Send + Sync + 'a,
+    E: ObjectType + Send + Sync + 'a,
+{
+    /// Creates a StreamDataSource from an `Iterator` of edges.
+    pub fn from_iter<I>(iter: I) -> Self
+    where
+        I: Iterator<Item = (Cursor, E, T)> + Send + Sync + 'a,
+    {
+        futures::stream::iter(iter).into()
+    }
+}
+
+impl<'a, S: Stream, T, E> From<S> for StreamDataSource<'a, T, E>
 where
     S: Stream<Item = (Cursor, E, T)> + Send + Sync + 'a,
     T: Send + Sync + 'a,
@@ -24,8 +92,7 @@ where
     }
 }
 
-use std::collections::VecDeque;
-struct State<T, E = EmptyEdgeFields>
+struct State<T, E>
 where
     T: Send + Sync,
     E: ObjectType + Send + Sync,