Flatten error handling, reducing generics

examples/customize_connection.rs

@@ -15,6 +15,7 @@ impl bb8::CustomizeConnection<DieselPgConn, ConnectionError> for ConnectionCusto
         connection
             .batch_execute_async("please execute some raw sql for me")
             .await
+            .map_err(ConnectionError::from)
     }
 }
 

examples/usage.rs

@@ -1,6 +1,5 @@
-use async_bb8_diesel::{
-    AsyncConnection, AsyncRunQueryDsl, AsyncSaveChangesDsl, ConnectionError, OptionalExtension,
-};
+use async_bb8_diesel::{AsyncConnection, AsyncRunQueryDsl, AsyncSaveChangesDsl, ConnectionError};
+use diesel::OptionalExtension;
 use diesel::{pg::PgConnection, prelude::*};
 
 table! {

src/async_traits.rs

@@ -18,42 +18,37 @@ use tokio::task::spawn_blocking;
 
 /// An async variant of [`diesel::connection::SimpleConnection`].
 #[async_trait]
-pub trait AsyncSimpleConnection<Conn, ConnErr>
+pub trait AsyncSimpleConnection<Conn>
 where
     Conn: 'static + SimpleConnection,
 {
-    async fn batch_execute_async(&self, query: &str) -> Result<(), ConnErr>;
+    async fn batch_execute_async(&self, query: &str) -> Result<(), DieselError>;
 }
 
 /// An async variant of [`diesel::connection::Connection`].
 #[async_trait]
-pub trait AsyncConnection<Conn, ConnErr>: AsyncSimpleConnection<Conn, ConnErr>
+pub trait AsyncConnection<Conn>: AsyncSimpleConnection<Conn>
 where
     Conn: 'static + DieselConnection,
-    ConnErr: From<DieselError> + Send + 'static,
     Self: Send,
 {
     type OwnedConnection: Sync + Send + 'static;
 
     #[doc(hidden)]
-    async fn get_owned_connection(&self) -> Result<Self::OwnedConnection, ConnErr>;
+    async fn get_owned_connection(&self) -> Self::OwnedConnection;
     #[doc(hidden)]
     fn as_sync_conn(owned: &Self::OwnedConnection) -> MutexGuard<'_, Conn>;
     #[doc(hidden)]
     fn as_async_conn(owned: &Self::OwnedConnection) -> &SingleConnection<Conn>;
 
     /// Runs the function `f` in an context where blocking is safe.
-    ///
-    /// Any error may be propagated through `f`, as long as that
-    /// error type may be constructed from `ConnErr` (as that error
-    /// type may also be generated).
     async fn run<R, E, Func>(&self, f: Func) -> Result<R, E>
     where
         R: Send + 'static,
-        E: From<ConnErr> + Send + 'static,
+        E: Send + 'static,
         Func: FnOnce(&mut Conn) -> Result<R, E> + Send + 'static,
     {
-        let connection = self.get_owned_connection().await?;
+        let connection = self.get_owned_connection().await;
         Self::run_with_connection(connection, f).await
     }
 
@@ -64,7 +59,7 @@ where
     ) -> Result<R, E>
     where
         R: Send + 'static,
-        E: From<ConnErr> + Send + 'static,
+        E: Send + 'static,
         Func: FnOnce(&mut Conn) -> Result<R, E> + Send + 'static,
     {
         spawn_blocking(move || f(&mut *Self::as_sync_conn(&connection)))
@@ -79,7 +74,7 @@ where
     ) -> Result<R, E>
     where
         R: Send + 'static,
-        E: From<ConnErr> + Send + 'static,
+        E: Send + 'static,
         Func: FnOnce(&mut Conn) -> Result<R, E> + Send + 'static,
     {
         spawn_blocking(move || f(&mut *Self::as_sync_conn(&connection)))
@@ -90,7 +85,7 @@ where
     async fn transaction<R, E, Func>(&self, f: Func) -> Result<R, E>
     where
         R: Send + 'static,
-        E: From<DieselError> + From<ConnErr> + Send + 'static,
+        E: From<DieselError> + Send + 'static,
         Func: FnOnce(&mut Conn) -> Result<R, E> + Send + 'static,
     {
         self.run(|conn| conn.transaction(|c| f(c))).await
@@ -99,21 +94,21 @@ where
     async fn transaction_async<R, E, Func, Fut, 'a>(&'a self, f: Func) -> Result<R, E>
     where
         R: Send + 'static,
-        E: From<DieselError> + From<ConnErr> + Send,
+        E: From<DieselError> + Send + 'static,
         Fut: Future<Output = Result<R, E>> + Send,
         Func: FnOnce(SingleConnection<Conn>) -> Fut + Send,
     {
         // Check out a connection once, and use it for the duration of the
         // operation.
-        let conn = Arc::new(self.get_owned_connection().await?);
+        let conn = Arc::new(self.get_owned_connection().await);
 
         // This function mimics the implementation of:
         // https://docs.diesel.rs/master/diesel/connection/trait.TransactionManager.html#method.transaction
         //
         // However, it modifies all callsites to instead issue
         // known-to-be-synchronous operations from an asynchronous context.
         Self::run_with_shared_connection(conn.clone(), |conn| {
-            Conn::TransactionManager::begin_transaction(conn).map_err(ConnErr::from)
+            Conn::TransactionManager::begin_transaction(conn).map_err(E::from)
         })
         .await?;
 
@@ -133,14 +128,14 @@ where
         match f(async_conn).await {
             Ok(value) => {
                 Self::run_with_shared_connection(conn.clone(), |conn| {
-                    Conn::TransactionManager::commit_transaction(conn).map_err(ConnErr::from)
+                    Conn::TransactionManager::commit_transaction(conn).map_err(E::from)
                 })
                 .await?;
                 Ok(value)
             }
             Err(user_error) => {
                 match Self::run_with_shared_connection(conn.clone(), |conn| {
-                    Conn::TransactionManager::rollback_transaction(conn).map_err(ConnErr::from)
+                    Conn::TransactionManager::rollback_transaction(conn).map_err(E::from)
                 })
                 .await
                 {
@@ -154,112 +149,108 @@ where
 
 /// An async variant of [`diesel::query_dsl::RunQueryDsl`].
 #[async_trait]
-pub trait AsyncRunQueryDsl<Conn, AsyncConn, E>
+pub trait AsyncRunQueryDsl<Conn, AsyncConn>
 where
     Conn: 'static + DieselConnection,
 {
-    async fn execute_async(self, asc: &AsyncConn) -> Result<usize, E>
+    async fn execute_async(self, asc: &AsyncConn) -> Result<usize, DieselError>
     where
         Self: ExecuteDsl<Conn>;
 
-    async fn load_async<U>(self, asc: &AsyncConn) -> Result<Vec<U>, E>
+    async fn load_async<U>(self, asc: &AsyncConn) -> Result<Vec<U>, DieselError>
     where
         U: Send + 'static,
         Self: LoadQuery<'static, Conn, U>;
 
-    async fn get_result_async<U>(self, asc: &AsyncConn) -> Result<U, E>
+    async fn get_result_async<U>(self, asc: &AsyncConn) -> Result<U, DieselError>
     where
         U: Send + 'static,
         Self: LoadQuery<'static, Conn, U>;
 
-    async fn get_results_async<U>(self, asc: &AsyncConn) -> Result<Vec<U>, E>
+    async fn get_results_async<U>(self, asc: &AsyncConn) -> Result<Vec<U>, DieselError>
     where
         U: Send + 'static,
         Self: LoadQuery<'static, Conn, U>;
 
-    async fn first_async<U>(self, asc: &AsyncConn) -> Result<U, E>
+    async fn first_async<U>(self, asc: &AsyncConn) -> Result<U, DieselError>
     where
         U: Send + 'static,
         Self: LimitDsl,
         Limit<Self>: LoadQuery<'static, Conn, U>;
 }
 
 #[async_trait]
-impl<T, AsyncConn, Conn, E> AsyncRunQueryDsl<Conn, AsyncConn, E> for T
+impl<T, AsyncConn, Conn> AsyncRunQueryDsl<Conn, AsyncConn> for T
 where
     T: 'static + Send + RunQueryDsl<Conn>,
     Conn: 'static + DieselConnection,
-    AsyncConn: Send + Sync + AsyncConnection<Conn, E>,
-    E: From<DieselError> + Send + 'static,
+    AsyncConn: Send + Sync + AsyncConnection<Conn>,
 {
-    async fn execute_async(self, asc: &AsyncConn) -> Result<usize, E>
+    async fn execute_async(self, asc: &AsyncConn) -> Result<usize, DieselError>
     where
         Self: ExecuteDsl<Conn>,
     {
-        asc.run(|conn| self.execute(conn).map_err(E::from)).await
+        asc.run(|conn| self.execute(conn)).await
     }
 
-    async fn load_async<U>(self, asc: &AsyncConn) -> Result<Vec<U>, E>
+    async fn load_async<U>(self, asc: &AsyncConn) -> Result<Vec<U>, DieselError>
     where
         U: Send + 'static,
         Self: LoadQuery<'static, Conn, U>,
     {
-        asc.run(|conn| self.load(conn).map_err(E::from)).await
+        asc.run(|conn| self.load(conn)).await
     }
 
-    async fn get_result_async<U>(self, asc: &AsyncConn) -> Result<U, E>
+    async fn get_result_async<U>(self, asc: &AsyncConn) -> Result<U, DieselError>
     where
         U: Send + 'static,
         Self: LoadQuery<'static, Conn, U>,
     {
-        asc.run(|conn| self.get_result(conn).map_err(E::from)).await
+        asc.run(|conn| self.get_result(conn)).await
     }
 
-    async fn get_results_async<U>(self, asc: &AsyncConn) -> Result<Vec<U>, E>
+    async fn get_results_async<U>(self, asc: &AsyncConn) -> Result<Vec<U>, DieselError>
     where
         U: Send + 'static,
         Self: LoadQuery<'static, Conn, U>,
     {
-        asc.run(|conn| self.get_results(conn).map_err(E::from))
-            .await
+        asc.run(|conn| self.get_results(conn)).await
     }
 
-    async fn first_async<U>(self, asc: &AsyncConn) -> Result<U, E>
+    async fn first_async<U>(self, asc: &AsyncConn) -> Result<U, DieselError>
     where
         U: Send + 'static,
         Self: LimitDsl,
         Limit<Self>: LoadQuery<'static, Conn, U>,
     {
-        asc.run(|conn| self.first(conn).map_err(E::from)).await
+        asc.run(|conn| self.first(conn)).await
     }
 }
 
 #[async_trait]
-pub trait AsyncSaveChangesDsl<Conn, AsyncConn, E>
+pub trait AsyncSaveChangesDsl<Conn, AsyncConn>
 where
     Conn: 'static + DieselConnection,
 {
-    async fn save_changes_async<Output>(self, asc: &AsyncConn) -> Result<Output, E>
+    async fn save_changes_async<Output>(self, asc: &AsyncConn) -> Result<Output, DieselError>
     where
         Self: Sized,
         Conn: diesel::query_dsl::UpdateAndFetchResults<Self, Output>,
         Output: Send + 'static;
 }
 
 #[async_trait]
-impl<T, AsyncConn, Conn, E> AsyncSaveChangesDsl<Conn, AsyncConn, E> for T
+impl<T, AsyncConn, Conn> AsyncSaveChangesDsl<Conn, AsyncConn> for T
 where
     T: 'static + Send + Sync + diesel::SaveChangesDsl<Conn>,
     Conn: 'static + DieselConnection,
-    AsyncConn: Send + Sync + AsyncConnection<Conn, E>,
-    E: 'static + Send + From<DieselError>,
+    AsyncConn: Send + Sync + AsyncConnection<Conn>,
 {
-    async fn save_changes_async<Output>(self, asc: &AsyncConn) -> Result<Output, E>
+    async fn save_changes_async<Output>(self, asc: &AsyncConn) -> Result<Output, DieselError>
     where
         Conn: diesel::query_dsl::UpdateAndFetchResults<Self, Output>,
         Output: Send + 'static,
     {
-        asc.run(|conn| self.save_changes(conn).map_err(E::from))
-            .await
+        asc.run(|conn| self.save_changes(conn)).await
     }
 }

src/connection.rs

@@ -1,6 +1,5 @@
 //! An async wrapper around a [`diesel::Connection`].
 
-use crate::{ConnectionError, ConnectionResult};
 use async_trait::async_trait;
 use diesel::r2d2::R2D2Connection;
 use std::sync::{Arc, Mutex, MutexGuard};
@@ -31,31 +30,30 @@ impl<C> Connection<C> {
 }
 
 #[async_trait]
-impl<Conn> crate::AsyncSimpleConnection<Conn, ConnectionError> for Connection<Conn>
+impl<Conn> crate::AsyncSimpleConnection<Conn> for Connection<Conn>
 where
     Conn: 'static + R2D2Connection,
 {
     #[inline]
-    async fn batch_execute_async(&self, query: &str) -> ConnectionResult<()> {
+    async fn batch_execute_async(&self, query: &str) -> Result<(), diesel::result::Error> {
         let diesel_conn = Connection(self.0.clone());
         let query = query.to_string();
         task::spawn_blocking(move || diesel_conn.inner().batch_execute(&query))
             .await
             .unwrap() // Propagate panics
-            .map_err(ConnectionError::from)
     }
 }
 
 #[async_trait]
-impl<Conn> crate::AsyncConnection<Conn, ConnectionError> for Connection<Conn>
+impl<Conn> crate::AsyncConnection<Conn> for Connection<Conn>
 where
     Conn: 'static + R2D2Connection,
-    Connection<Conn>: crate::AsyncSimpleConnection<Conn, ConnectionError>,
+    Connection<Conn>: crate::AsyncSimpleConnection<Conn>,
 {
     type OwnedConnection = Connection<Conn>;
 
-    async fn get_owned_connection(&self) -> Result<Self::OwnedConnection, ConnectionError> {
-        Ok(Connection(self.0.clone()))
+    async fn get_owned_connection(&self) -> Self::OwnedConnection {
+        Connection(self.0.clone())
     }
 
     fn as_sync_conn(owned: &Self::OwnedConnection) -> MutexGuard<'_, Conn> {