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如何从两个不同的外键访问模型?

activerecord ruby-on-rails-4 postgresql ruby ruby-on-rails

Ulysse BN · 技术社区 · 6 年前

我有两个相关的模型,旅行和乘坐。一次旅行可能有一次旅行或一次回程旅行。我的ActiveRecord模型如下:

class Route < ActiveRecord::Base
    has_one :trip
end

class Trip < ActiveRecord::Base
    belongs_to :going_route,     class_name: "Route"
    belongs_to :returning_route, class_name: "Route"
end

但是,当我想从一条路线上访问一次旅行时,这会给我带来一个问题:

Route.first.trip

这将引发PostgreSQL错误:

pg::undefinedcolumn:错误:列trips.route id不存在

我怎样才能告诉 Route 他旅行的班级 going_route_id 或 returning_route_id ?或者也许还有别的办法?

P.S:我一直在寻找类似的问题,有很多,但没有一个完全像这个问题,解决了我的问题。如果你对如何使区别更清楚有什么建议,尤其是标题。 Here 是类似的问题吗

编辑:

我也试过使用lambda,比如 matthew's duplicate proposition :

class FavoriteRoute < ActiveRecord::Base
    has_one :favorite_trip, -> (route) { where("going_route_id = :id OR returning_route_id = :id", id: route.id) }
end

这将引发相同的错误。如果我认为我应该使用 find_by 而不是 where 因为我只需要一个结果,我还有一个错误,我真的不明白:

nomethodError:未定义的方法'except',用于行程:0x0007F827B9D13E0>

4 回复 | 直到 5 年前

max Mike Williams 6 年前

belongs_to has_one has_many

class Trip < ActiveRecord::Base
    # specifying foreign_key here is not needed since AR
    # will deduce that its outbound_route_id
    belongs_to :outbound_route,
      class_name: "Route"
    belongs_to :return_route, 
      class_name: "Route"
end

class Route < ActiveRecord::Base
  has_one :trip_as_outbound,
    class_name: 'Trip',
    foreign_key: :outbound_route_id
  has_one :trip_as_returning,
    class_name: 'Trip',
    foreign_key: :return_route_id

  def trip
    trip_as_outbound || trip_as_returning
  end
end

class Route < ApplicationRecord 
end

class Routes::Outbound < ::Route
  self.table_name = 'routes'
  has_one :trip, foreign_key: :outbound_route_id
end

class Routes::Return < ::Route
  self.table_name = 'routes'
  has_one :trip, foreign_key: :return_route_id
end

class Trip < ApplicationRecord
  belongs_to :outbound_route,
    class_name: '::Routes::Outbound'
  belongs_to :return_route,
    class_name: '::Routes::Return'
end

Routes::Return.all Route.all

type routes

Jocko 6 年前

going returning

trip_routes

create_table :trip_routes do |t|
   t.integer :trip_id
   t.integer :route_id
   t.string  :route_type
   t.boolean :favorite
end

# Consider this part based on how you think your indexes are best built, I'm 
# just making note that DB performance can be impacted particularly on these
# two fields.
add_index :trip_routes, :trip_id
add_index :trip_routes, :route_id

trip_route

class TripRoute < ActiveRecord::Base
    belongs_to :trip
    belongs_to :route

    # This model knows whether it's the 'going' or 'returning' route, so do your 
    # route functionality here.
end

trip

class Trip < ActiveRecord::Base
    has_many :trip_routes
    has_many :route, through: trip_routes

    # Helper to get the going route
    def going_trip_route
        self.trip_routes.find_by(route_type: "going")
    end

    # Helper to get the going route
    def returning_trip_route
        self.trip_routes.find_by(route_type: "returning")
    end

end

route

class Route < ActiveRecord::Base
    has_many :trip_routes
    has_many :trips, through: trip_routes
end

Ulysse BN 6 年前

class Route
    def trip
        @trip ||= Trip.find_by("going_route_id = :id OR returning_route_id = :id", id: id)
    end
end

Christian Angel Galamay 6 年前

add_column :routes, :going_key,     :integer
add_column :routes, :returning_key, :integer

class Route < ActiveRecord::Base
  belongs_to :going_route, foreign_key: :going_key, class_name: Trip
  belongs_to :returning_route, foreign_key: :returning_key, class_name: Trip
end

class Trip < ActiveRecord::Base
end

Route.first.going_route 
Route.first.returning_route