Rails 5.2 多态关联与多态条件

Question

型号：

class Car < ApplicationRecord
  belongs_to :user

  has_one  :listing, as: :listable
  has_one  :firm, as: :firmable
  has_one  :seller, as: :sellable
end

class Truck < ApplicationRecord
  belongs_to :user

  has_one  :listing, as: :listable
  has_one  :firm, as: :firmable
  has_one  :seller, as: :sellable
end

class Listing < ApplicationRecord
  belongs_to :listable, polymorphic: true
  has_many :favorites, dependent: :destroy
  has_many :users_who_favorited, through: :favorites, source: :user
end

并假设 Car 和 Truck 都有一个 user_id 字段....

Listing.includes(:listable) returns 一个 eargerloaded listings AR 关系。

但是，我需要按 user_id 进行筛选，所以我尝试...

Listing.includes(:listable).where(user_id: 100)

但是我得到一个错误..

ActiveRecord::StatementInvalid (PG::UndefinedColumn: ERROR: column listings.user_id does not exist) LINE 1: SELECT "listings".* FROM "listings" WHERE "listings"."user_...

因为它似乎在查找 user_id 列表。但是，我需要在 listables table 上进行过滤，因此这意味着 Car 或 Truck tables。然而 listable 被定义了。

我也试过：

Listing.includes(listable:[:user]).where('users.id = 100')

但我明白了...

ActiveRecord::StatementInvalid (PG::UndefinedTable: ERROR: missing FROM-clause entry for table "users") LINE 1: SELECT "listings".* FROM "listings" WHERE (users.id = 100) ... ^ : SELECT "listings".* FROM "listings" WHERE (users.id = 100) LIMIT

更新：

然后试了

class Listing < ApplicationRecord
  belongs_to :listable, polymorphic: true
  has_many :favorites, dependent: :destroy
  has_many :users_who_favorited, through: :favorites, source: :user

  belongs_to :car, -> { includes(:listable).where(listable: { listable_type: Car.to_s }) }, foreign_key: :listable_id
  belongs_to :truck, -> { includes(:listable).where(listable: { listable_type: Truck.to_s }) }, foreign_key: :listable_id

end

并尝试了 Listing.includes(:car, :truck) 但得到了..

ActiveRecord::ConfigurationError (Can't join 'Car' to association named 'listable'; perhaps you misspelled it?)

因此，在上面的方法起作用之前，我无法尝试下面的方法。

Listing.includes(:car, :truck).where(cars: { user_id: 1 }).or(Listing.includes(:car, :truck).where(trucks: { user_id: 1 }))

但是，我可以做到 Listing.includes(:listable) 它确实有效，当我添加条件时它会中断。

Answer 1

这是一个非常有趣的问题，我问了好几个月。然后我找到了解决办法。

在您的 Listing 模型中，为了能够包含您的 polymorphic 模型，您需要告诉您的模型它们是相关的。

class Car < ApplicationRecord
  belongs_to :user

  has_one  :listing, as: :listable
  has_one  :firm, as: :firmable
  has_one  :seller, as: :sellable
end

class Truck < ApplicationRecord
  belongs_to :user

  has_one  :listing, as: :listable
  has_one  :firm, as: :firmable
  has_one  :seller, as: :sellable
end

class Listing < ApplicationRecord
  belongs_to :listable, polymorphic: true
  has_many :favorites, dependent: :destroy
  has_many :users, through: :favorites

  #magic happens here
  belongs_to :car, -> { includes(:listable).where(listings: { listable_type: Car.to_s }) }, foreign_key: :listable_id
  belongs_to :truck, -> { includes(:listable).where(listings: { listable_type: Truck.to_s }) }, foreign_key: :listable_id

end

现在，您只需执行以下操作：Listing.includes(:car, :truck)，它将完美运行:-)

针对您的情况：

Listing.includes(:car, :truck).where(cars: { user_id: 1 }).or(Listing.includes(:car, :truck).where(trucks: { user_id: 1 }))

Answer 2

对于那些可能和我一样难以解决这个问题的人...

我的最终解决方案：

    def left_join_listable(table_name, listable_type_value)
      "LEFT OUTER JOIN \"#{table_name}\" "\
      "ON \"#{table_name}\".\"id\" = \"listings\".\"listable_id\" "\
      "AND \"listings\".\"listable_type\" = #{listable_type_value}"
    end

   def left_join_users_on(*table_names)
      join = "LEFT OUTER JOIN \"users\" ON "
      conditionals = table_names.map {|table_name| "\"users\".\"id\" = \"#{table_name}\".\"user_id\"" }.join(" OR ")
      join + conditionals
    end

Listing.joins(left_join_listable('cars',"\'Car\'"))
       .joins(left_join_listable('trucks',"\'Trucks\'"))
       .joins(left_join_users_on('cars','trucks')
       .where(users.id = (?), 100)

Rails 5.2 多态关联与多态条件

Rails 5.2 Polymorphic Association with polymorphic conditional

ruby-on-rails

ruby

polymorphism

ruby-on-rails-5.2

型号：

更新：

我的最终解决方案：