perf(backend): avoid N+1 selects from user table when packing many entities (#13911)

* perf(backend): avoid N+1 selects from `user` table when packing many entities

* perf(backend): use `packMany` instead of mapping to `pack`

packages/backend/src/server/api/endpoints/roles/users.ts

@@ -92,9 +92,12 @@ export default class extends Endpoint<typeof meta, typeof paramDef> { // eslint-
 				.limit(ps.limit)
 				.getMany();
 
+			const _users = assigns.map(({ user, userId }) => user ?? userId);
+			const _userMap = await this.userEntityService.packMany(_users, me, { schema: 'UserDetailed' })
+				.then(users => new Map(users.map(u => [u.id, u])));
 			return await Promise.all(assigns.map(async assign => ({
 				id: assign.id,
-				user: await this.userEntityService.pack(assign.user!, me, { schema: 'UserDetailed' }),
+				user: _userMap.get(assign.userId) ?? await this.userEntityService.pack(assign.user!, me, { schema: 'UserDetailed' }),
 			})));
 		});
 	}