平均值范围

Question

我正在尝试在我的电影模型上定义一个范围，以便 select 所有平均评分高于所提供值的电影。

到目前为止我有以下型号：

class Movie < ActiveRecord::Base
  # Callbacks & Plugins

  # Associations
  has_and_belongs_to_many :categories
  has_many :ratings

  # Validations
  validates :name, presence: true, uniqueness: true
  validates :description, presence: true

  # Scopes
  scope :category, -> (category) { joins(:categories).where("categories.id = ?", category) }
  scope :searchable, -> (query) { where("name LIKE '%?%'", query) }
  scope :rating, -> (rating) { joins(:ratings).average("ratings.value")) }
end

class Rating < ActiveRecord::Base
  # Callback & plugins

  # Associations
  belongs_to :user
  belongs_to :movie, counter_cache: true

  # Validations
  validates :value, presence: true, numericality: { only_integer: true, greater_than_or_equal_to: 1, less_than_or_equal_to: 5 }
  validates :user, presence: true, uniqueness: { scope: :movie_id }
end

现在我正在研究 Rails 中的查询选项。我想要做的是有一个 select 特定电影的所有评级的范围。使用评级的值属性计算平均值。如果该值等于或高于提供的值，则该电影是 selected.

在代码中我一直在玩 joins 和 average 查询选项，但我不确定如何将它们结合起来得到我想要的。

Answer 1

我想我找到了...

scope :rating, -> (rating) { joins(:ratings).group("movies.id").having("AVG(ratings.value) > ? OR AVG(ratings.value) = ?", rating, rating) }

为我生成以下查询：

 Movie Load (1.9ms)  SELECT "movies".* FROM "movies" INNER JOIN "ratings" ON "ratings"."movie_id" = "movies"."id" GROUP BY movies.id HAVING AVG(ratings.value) > 1 OR AVG(ratings.value) = 1

我想我想要的。现在将用一些 Rspec 来测试它是否有效。

平均值范围

Scope on average value

sql

activerecord

ruby-on-rails