我有一个关系模型,其中两个用户可以进行交易以交换两个项目。
class User < ActiveRecord::Base
has_many :owned_items, class_name: "Item"
has_many :trades_received, class_name: "Trade", through: :owned_items, source: :trades
has_many :trades
has_many :wanted_items, class_name: "Item", through: :trades, source: :item
end
class Item < ActiveRecord::Base
belongs_to :owner, class_name: "User", foreign_key: :user_id
has_many :trades, dependent: :destroy
has_many :trade_requesters, through: :trades
has_many :trade_recipients, through: :trades
end
class Trade < ActiveRecord::Base
belongs_to :trade_requester, class_name: "User"
belongs_to :trade_recipient, class_name: "User"
belongs_to :wanted_item, class_name: "Item", foreign_key: :wanted_item_id
belongs_to :collateral_item, class_name: "Item", foreign_key: :collateral_item_id
end
我的 Trades 表上的迁移如下所示:
create_table :trades do |t|
t.belongs_to :trade_requester
t.belongs_to :trade_recipient
t.belongs_to :wanted_item
t.belongs_to :collateral_item
end
堆栈跟踪指向我用来列出所有交易请求的辅助方法。该行表示 @trades = current_user.trades_received.requested.count
,然后向下到 User 上的模型关联,其中 has_many :owned_items, class_name: "Item"
。根据我的理解,它看起来像 trades_received
方法,它被称为 through: :owned_items
和 source::trades
应该引用 :wanted_item_id
迁移中的外键。但事实并非如此。如果我创建一个迁移以添加 item_id
,它会起作用,但是一个 Trade 需要两个项目,所以我将它分成两个 wanted_item
和 collateral_item
协会。我如何设置该用户关联,以便它引用另一个用户正在请求的项目? Items has_many :trades
应该是我拥有的方式,还是应该 Items belongs_to :trades
?
完整错误:
PG::UndefinedColumn: ERROR: column trades.item_id does not exist
LINE 1: ...LECT COUNT(*) FROM "trades" INNER JOIN "items" ON "trades"."...
^
: SELECT COUNT(*) FROM "trades" INNER JOIN "items" ON "trades"."item_id" = "items"."id" WHERE "items"."user_id" = $1 AND "trades"."approved" IS NULL
tldr:我需要跟踪一堆复杂的 has_many :through
关联,我认为我的数据模型不正确,需要帮助理解原因。谢谢。
最佳答案
你在 User
和 Item
之间建立了两个 has_many :through
关系,以 Trade
作为加入两者的表。你有一些关系混淆。这是基于您的迁移的设置:
class User < ActiveRecord::Base
has_many :received_trades, class_name: "Trade", foreign_key: "trade_recipient"
has_many :requested_trades, class_name: "Trade", foreign_key: "trade_requester"
has_many :collateral_items, through: :received_trades
has_many :wanted_items, through: :requested_trades
end
class Item < ActiveRecord::Base
has_many :collateral_items, class_name: "Trade", foreign_key: "collateral_item"
has_many :wanted_items, class_name: "Trade", foreign_key: "wanted_item"
has_many :trade_requesters, through: :wanted_items
has_many :trade_recipients, through: :collateral_items
end
class Trade < ActiveRecord::Base
belongs_to :trade_requester, class_name: "User"
belongs_to :trade_recipient, class_name: "User"
belongs_to :wanted_item, class_name: "Item"
belongs_to :collateral_item, class_name: "Item"
end
##migration
create_table :trades do |t|
t.belongs_to :trade_requester
t.belongs_to :trade_recipient
t.belongs_to :wanted_item
t.belongs_to :collateral_item
end
一些解释:
Item has_many :collateral_item ## item_id in table collateral_items
Item has_many :collateral_item, class_name: "Trade", foreign_key: "collateral_item"
##collateral_item_id in trades table.
关于ruby-on-rails - 为什么列 trades.item_id 不存在?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/46045484/