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/core/entities/PageEntityService.ts

@@ -40,6 +40,9 @@ export class PageEntityService {
 	public async pack(
 		src: MiPage['id'] | MiPage,
 		me?: { id: MiUser['id'] } | null | undefined,
+		hint?: {
+			packedUser?: Packed<'UserLite'>
+		},
 	): Promise<Packed<'Page'>> {
 		const meId = me ? me.id : null;
 		const page = typeof src === 'object' ? src : await this.pagesRepository.findOneByOrFail({ id: src });
@@ -91,7 +94,7 @@ export class PageEntityService {
 			createdAt: this.idService.parse(page.id).date.toISOString(),
 			updatedAt: page.updatedAt.toISOString(),
 			userId: page.userId,
-			user: this.userEntityService.pack(page.user ?? page.userId, me), // { schema: 'UserDetailed' } すると無限ループするので注意
+			user: hint?.packedUser ?? this.userEntityService.pack(page.user ?? page.userId, me), // { schema: 'UserDetailed' } すると無限ループするので注意
 			content: page.content,
 			variables: page.variables,
 			title: page.title,
@@ -110,11 +113,14 @@ export class PageEntityService {
 	}
 
 	@bindThis
-	public packMany(
+	public async packMany(
 		pages: MiPage[],
 		me?: { id: MiUser['id'] } | null | undefined,
 	) {
-		return Promise.all(pages.map(x => this.pack(x, me)));
+		const _users = pages.map(({ user, userId }) => user ?? userId);
+		const _userMap = await this.userEntityService.packMany(_users, me)
+			.then(users => new Map(users.map(u => [u.id, u])));
+		return Promise.all(pages.map(page => this.pack(page, me, { packedUser: _userMap.get(page.userId) })));
 	}
 }