Avoid async overhead for sync reads

drift/lib/src/runtime/api/connection_user.dart

@@ -19,7 +19,7 @@ abstract class DatabaseConnectionUser {
 
   /// A [SqlTypes] mapping configuration to use when mapping values between Dart
   /// and SQL.
-  SqlTypes get typeMapping => options.createTypeMapping(executor.dialect);
+  late final SqlTypes typeMapping = options.createTypeMapping(executor.dialect);
 
   /// The database class that this user is attached to.
   @visibleForOverriding

drift/lib/src/runtime/query_builder/statements/select/select.dart

@@ -87,8 +87,8 @@ class SimpleSelectStatement<T extends HasResultSet, D> extends Query<T, D>
     return table.map(row);
   }
 
-  Future<List<D>> _mapResponse(List<Map<String, Object?>> rows) {
-    return rows.mapAsyncAndAwait(_mapRow);
+  FutureOr<List<D>> _mapResponse(List<Map<String, Object?>> rows) {
+    return rows.mapAsyncAndAwait(table.map);
   }
 
   /// Creates a select statement that operates on more than one table by

drift/lib/src/utils/async.dart

@@ -6,7 +6,12 @@ import 'package:meta/meta.dart';
 /// Drift-internal utilities to map potentially async operations.
 extension MapAndAwait<T> on Iterable<T> {
   /// A variant of [Future.wait] that also works for [FutureOr].
-  Future<List<R>> mapAsyncAndAwait<R>(FutureOr<R> Function(T) mapper) {
+  FutureOr<List<R>> mapAsyncAndAwait<R>(FutureOr<R> Function(T) mapper) {
+    if (mapper is R Function(T)) {
+      // It's actually all synchronous
+      return map(mapper).toList();
+    }
+
     return Future.wait(map((e) => Future.sync(() => mapper(e))));
   }
 }

drift/lib/src/utils/async_map.dart

@@ -15,14 +15,14 @@ extension AsyncMapPerSubscription<S> on Stream<S> {
   /// controller. Since we need the behavior of `asyncMap` internally though, we
   /// re-implement it in a simple variant that transforms each subscription
   /// individually.
-  Stream<T> asyncMapPerSubscription<T>(Future<T> Function(S) mapper) {
+  Stream<T> asyncMapPerSubscription<T>(FutureOr<T> Function(S) mapper) {
     return Stream.multi(
       (listener) {
         late StreamSubscription<S> subscription;
 
         void onData(S original) {
           subscription.pause();
-          mapper(original)
+          Future.sync(() => mapper(original))
               .then(listener.addSync, onError: listener.addErrorSync)
               .whenComplete(subscription.resume);
         }