controllers/version: Pipelining database queries

src/controllers/version/metadata.rs

@@ -25,8 +25,10 @@ use super::CrateVersionPath;
 pub async fn find_version(state: AppState, path: CrateVersionPath) -> AppResult<ErasedJson> {
     let mut conn = state.db_read().await?;
     let (version, krate) = path.load_version_and_crate(&mut conn).await?;
-    let published_by = version.published_by(&mut conn).await?;
-    let actions = VersionOwnerAction::by_version(&mut conn, &version).await?;
+    let (actions, published_by) = tokio::try_join!(
+        VersionOwnerAction::by_version(&mut conn, &version),
+        version.published_by(&mut conn),
+    )?;
 
     let version = EncodableVersion::from(version, &krate.name, published_by, actions);
     Ok(json!({ "version": version }))

src/controllers/version/update.rs

@@ -71,8 +71,10 @@ pub async fn update_version(
     )
     .await?;
 
-    let published_by = version.published_by(&mut conn).await?;
-    let actions = VersionOwnerAction::by_version(&mut conn, &version).await?;
+    let (actions, published_by) = tokio::try_join!(
+        VersionOwnerAction::by_version(&mut conn, &version),
+        version.published_by(&mut conn),
+    )?;
     let updated_version = EncodableVersion::from(version, &krate.name, published_by, actions);
     Ok(json!({ "version": updated_version }))
 }

src/models/action.rs

@@ -5,6 +5,8 @@ use chrono::NaiveDateTime;
 use crates_io_diesel_helpers::pg_enum;
 use diesel::prelude::*;
 use diesel_async::{AsyncPgConnection, RunQueryDsl};
+use futures_util::future::BoxFuture;
+use futures_util::future::FutureExt;
 
 pg_enum! {
     pub enum VersionAction {
@@ -54,18 +56,18 @@ impl VersionOwnerAction {
         version_owner_actions::table.load(conn).await
     }
 
-    pub async fn by_version(
+    pub fn by_version<'a>(
         conn: &mut AsyncPgConnection,
-        version: &Version,
-    ) -> QueryResult<Vec<(Self, User)>> {
+        version: &'a Version,
+    ) -> BoxFuture<'a, QueryResult<Vec<(Self, User)>>> {
         use version_owner_actions::dsl::version_id;
 
         version_owner_actions::table
             .filter(version_id.eq(version.id))
             .inner_join(users::table)
             .order(version_owner_actions::dsl::id)
             .load(conn)
-            .await
+            .boxed()
     }
 
     pub async fn for_versions(