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在我的 Rails 应用程序中，我遇到了 N+1 问题，我需要对数据库进行额外调用以一遍又一遍地获取相关数据，特别是在记录每个模型的印象数时。

例如：

Started GET "/" for 127.0.0.1 at 2018-12-02 16:21:05 -0500
Processing by JobsController#index as HTML
  Job Load (4.4ms)  SELECT  "jobs".* FROM "jobs" WHERE "jobs"."published_at" IS NOT NULL ORDER BY "jobs"."published_at" DESC LIMIT $1 OFFSET $2  [["LIMIT", 30], ["OFFSET", 0]]
  ↳ app/controllers/jobs_controller.rb:22
  User Load (1.1ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 ORDER BY "users"."id" ASC LIMIT $2  [["id", 13], ["LIMIT", 1]]
  ↳ app/controllers/jobs_controller.rb:24
  Impression Exists (1.3ms)  SELECT  1 AS one FROM "impressions" WHERE "impressions"."impressionable_id" = $1 AND "impressions"."impressionable_type" = $2 AND "impressions"."session_hash" = $3 LIMIT $4  [["impressionable_id", 705], ["impressionable_type", "Job"], ["session_hash", "d80d52dd401011a626d600167140e49f"], ["LIMIT", 1]]
  ↳ app/controllers/jobs_controller.rb:24
  Impression Exists (0.6ms)  SELECT  1 AS one FROM "impressions" WHERE "impressions"."impressionable_id" = $1 AND "impressions"."impressionable_type" = $2 AND "impressions"."session_hash" = $3 LIMIT $4  [["impressionable_id", 704], ["impressionable_type", "Job"], ["session_hash", "d80d52dd401011a626d600167140e49f"], ["LIMIT", 1]]
  ↳ app/controllers/jobs_controller.rb:24
  Impression Exists (0.4ms)  SELECT  1 AS one FROM "impressions" WHERE "impressions"."impressionable_id" = $1 AND "impressions"."impressionable_type" = $2 AND "impressions"."session_hash" = $3 LIMIT $4  [["impressionable_id", 703], ["impressionable_type", "Job"], ["session_hash", "d80d52dd401011a626d600167140e49f"], ["LIMIT", 1]]
  ↳ app/controllers/jobs_controller.rb:24

我正在使用印象派宝石并impressionist直接使用该方法，获取Jobs页面上的所有内容并记录印象。问题是因为我只记录独特的印象，对于已经有的记录impression，这些额外的调用是多余的。我试图用它@jobs.includes(:impressions).each来预加载相关数据，希望 Rails 足够聪明，可以找出存在哪些记录，但 Rails 仍然会输出大量Impression Exists查询。

@jobs.each{|job| impressionist(job,'', :unique => [:session_hash])}
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