Rails 4 ActiveRecord 按关联计数排序

Question

有一个视图我要显示的内容

例如：

recipe.user.name 
recipe.name
recipe.picture
recipe.created_at

排序

recipe.likes.count

控制器：

@recipes_by_likes = Recipe.likes_count.paginate(page: params[:page])

型号：

Recipe has_many :likes

和

Like belongs_to :recipe

范围：

scope :likes_count, -> { 
  select('recipes.*, COUNT(likes.id) AS likes_count').
  joins(:likes).
  order('likes_count DESC')
}

但这给了我

SELECT  recipes.*, COUNT(likes.id) AS likes_count 
FROM "recipes" 
INNER JOIN "likes" ON "likes"."recipe_id" = "recipes"."id"  
ORDER BY "recipes"."created_at" DESC, likes_count DESC 
LIMIT 30 OFFSET 0

只返回 1 个（错误的）结果。

Answer 1

1。查询

您不应该通过他们的id 来计算喜欢，因为它始终是唯一的并且总是返回 1，而是通过 recipe_id 这与某个食谱相关联的喜欢相同。

scope :likes_count, -> { 
  select('recipes.*, COUNT(likes.recipe_id) AS likes_count')
  .joins(:likes)
  .group('recipes.id')
  .order('likes_count DESC')
}

2。计数器缓存方法

您也可以使用counter_cache

class Like < ActiveRecord::Base
  belongs_to :recipe, counter_cache: true
end

并为Recipe模型添加一列

add_column :recipes, :likes_count, :integer, default: 0