通过 has_many 关系基于多个对象的 ActiveRecord 查询

Question

我有一个Product 类，它是has_many Gender 到Connection 类实例。我想查询以查找同时具有end_a 和end_b 的产品。当前的类方法有两个注意事项：

• 如果搜索end_a 和end_b 相同的位置，则无法正确返回。相反，应该搜索 product 是否有 2 个实例，而不仅仅是一个对象。
• 当我想要 ActiveRecord_Relation 时返回 Array。

类方法.query如下，欢迎反馈或意见。

class Product < ActiveRecord::Base

  has_many   :connections, dependent: :destroy, as: :connectionable
  has_many   :genders,     through:   :connections

  def self.query(end_a, end_b)
    search_base = active.joins(:connections)
    end_a_search = search_base.where(connections: { gender_id: end_a  } )

    end_a_search & search_base.where(connections: { gender_id: end_b  } )
  end
end

ps：一旦解决这个问题，很可能会将其移至Product 的范围内

Answer 1

class Product < ActiveRecord::Base
  has_many :connections, dependent: :destroy, as: :connectionable
  has_many :genders, through: :connections

  scope :with_genders, -> (end_a, end_b) {
    relation = joins('INNER JOIN connections c1 ON c1.connectionable_id = products.id AND c1.connectionable_type = \'Product\'')
      .joins('INNER JOIN connections c2 ON c1.connectionable_id = c2.connectionable_id AND c2.connectionable_type = \'Product\'')
      .where(c1: {gender_id: end_a}, c2: {gender_id: end_b})
      .group('products.id')
    end_a == end_b ? relation.having('COUNT(products.id) > 1') : relation
  }
end