Question

class Project < ActiveRecord::Base
 has_many :photos, -> { order(main: :desc, id: :asc) }, as: :photoable, class_name: 'Photo', dependent: :destroy

class Photo < ActiveRecord::Base
  belongs_to :photoable, polymorphic: true

projects = Project.limit(10).includes(:photos)

SELECT  "projects".* FROM "projects" WHERE "projects"."is_deleted" = $1 LIMIT 10  [["is_deleted", "f"]]
Photo Load (0.5ms)  SELECT "photos".* FROM "photos" WHERE "photos"."photoable_type" = 'Project' AND "photos"."photoable_id" IN (1, 403, 371, 8784, 12, 34, 11, 1111, 31, 22)  ORDER BY "photos"."main" DESC, "photos"."id" ASC

 projects.first.photo
 Photo Load (0.6ms)

它正在发送一个在（0.6ms）内执行的数据库查询。知道如何避免数据库查询吗？

我正在使用Rails 4.2.6＆amp; Ruby 2.3.1p112

Answer 1

projects = Project.includes(:photos).limit(10)

然后遍历项目。它不会触发另一个查询。

projects.each do |project|
  project.photo
end

Rails预加载不适用于多态关系

1 个答案: