0 
 <%- @lessons.includes(:bookmarks).each_with_index do |lesson, index| -%>
          <tr>
            <td class="w6 pl">
              <%- bookmark = lesson.bookmarks.where(user_id: current_user).first -%>
              <%= render :partial => "student/lessons/bookmark", :locals => {:bookmark => bookmark, :lesson => lesson} %>
            </td>
          </tr>
 <%- end -%>

上記のコードは、次のN+1クエリを生成します。

  Bookmark Load (0.3ms)  SELECT "bookmarks".* FROM "bookmarks" WHERE "bookmarks"."lesson_id" IN (1, 2, 3, 4, 5, 6)
  Bookmark Load (0.3ms)  SELECT "bookmarks".* FROM "bookmarks" WHERE "bookmarks"."lesson_id" = 1 AND "bookmarks"."user_id" = 1 LIMIT 1
Rendered student/lessons/_bookmark.html.erb (1.4ms)
  Bookmark Load (0.3ms)  SELECT "bookmarks".* FROM "bookmarks" WHERE "bookmarks"."lesson_id" = 2 AND "bookmarks"."user_id" = 1 LIMIT 1
Rendered student/lessons/_bookmark.html.erb (0.6ms)
  Bookmark Load (0.3ms)  SELECT "bookmarks".* FROM "bookmarks" WHERE "bookmarks"."lesson_id" = 3 AND "bookmarks"."user_id" = 1 LIMIT 1
Rendered student/lessons/_bookmark.html.erb (0.6ms)
  Bookmark Load (0.3ms)  SELECT "bookmarks".* FROM "bookmarks" WHERE "bookmarks"."lesson_id" = 4 AND "bookmarks"."user_id" = 1 LIMIT 1
Rendered student/lessons/_bookmark.html.erb (0.6ms)
  Bookmark Load (0.2ms)  SELECT "bookmarks".* FROM "bookmarks" WHERE "bookmarks"."lesson_id" = 5 AND "bookmarks"."user_id" = 1 LIMIT 1
Rendered student/lessons/_bookmark.html.erb (0.6ms)
  Bookmark Load (0.1ms)  SELECT "bookmarks".* FROM "bookmarks" WHERE "bookmarks"."lesson_id" = 6 AND "bookmarks"."user_id" = 1 LIMIT 1

ループ内でwhereクエリを使用しているので、最初のクエリの後に追加のクエリを防ぐにはどうすればよいですか？

ありがとう！

4

1 に答える 1

2

2 つのクエリを手動で実行する必要があります。

@lessons = Lesson.all # i.e.
@bookmarks = Bookmark.select("bookmarks.*, DISTINCT(lesson_id)").where(user_id: current_user.id)

その後

@lessons.each do |lesson|
  ...
  bookmark = @bookmarks.detect{ |b| b.lesson_id == lesson.id }
  ...
end
于 2012-06-13T20:42:09.130 に答える