Question

我似乎无法弄清楚为什么这种关联不起作用：我不确定如何比提供代码示例更好地描述情况：

这是我的应用程序环境：

Ruby version              1.8.7 (universal-darwin10.0)
Rails version             2.3.3

代码示例：

class Account
 has_one :subscription
 has_one :package, :through => :subscription
end

class Subscription
 belongs_to :account
 belongs_to :package
end

class Package
 has_many :subscriptions
 has_many :accounts, :through => :subscriptions
end

>> Account.first.subscription
=> #<Subscription id: 1, account_id: 25, package_id: 4>

>> Account.first.subscription.package
=> #<Package id: 4, name: "Bronze Package">

>> Package.first.accounts
=> [#<Account id: 25, subdomain: "bigbangtechnology">]

>> Package.first.subscriptions
=> [#<Subscription id: 1, account_id: 25, package_id: 4>]

>> Account.first.package
  Package Load (0.0ms)   Mysql::Error: Unknown column 'packages.account_id' in 'where clause': SELECT `packages`.* FROM `packages` WHERE (packages.account_id = 25 ) 
ActiveRecord::StatementInvalid: Mysql::Error: Unknown column 'packages.account_id' in 'where clause': SELECT `packages`.* FROM `packages`    WHERE (packages.account_id = 25 ) 
 from /Users/camwest/Sites/yardstickapp/vendor/rails/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb:212:in `log'
 from /Users/camwest/Sites/yardstickapp/vendor/rails/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb:320:in `execute'
 from /Users/camwest/Sites/yardstickapp/vendor/rails/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb:595:in `select'
 from /Users/camwest/Sites/yardstickapp/vendor/rails/activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb:7:in `select_all_without_query_cache'
 from /Users/camwest/Sites/yardstickapp/vendor/rails/activerecord/lib/active_record/connection_adapters/abstract/query_cache.rb:62:in `select_all'
 from /Users/camwest/Sites/yardstickapp/vendor/rails/activerecord/lib/active_record/base.rb:661:in `find_by_sql'
 from /Users/camwest/Sites/yardstickapp/vendor/rails/activerecord/lib/active_record/base.rb:1548:in `find_every'
 from /Users/camwest/Sites/yardstickapp/vendor/rails/activerecord/lib/active_record/base.rb:615:in `find'
 from /Users/camwest/Sites/yardstickapp/vendor/rails/activerecord/lib/active_record/associations/has_many_through_association.rb:73:in `find_target'
 from /Users/camwest/Sites/yardstickapp/vendor/rails/activerecord/lib/active_record/associations/has_one_through_association.rb:23:in `find_target'
 from /Users/camwest/Sites/yardstickapp/vendor/rails/activerecord/lib/active_record/associations/association_collection.rb:353:in `load_target'
 from /Users/camwest/Sites/yardstickapp/vendor/rails/activerecord/lib/active_record/associations/association_proxy.rb:112:in `reload'
 from /Users/camwest/Sites/yardstickapp/vendor/rails/activerecord/lib/active_record/associations.rb:1219:in `package'
 from (irb):22

Answer 1

从Rails 2.2.1开始，您可以使用委托：

class Account
  delegate :package, :to => :subscription
end

http://apidock.com/rails/Module/delegate

Answer 2

通过阅读文档看起来我找到了答案：

<强>：通过

指定用于执行查询的连接模型。以下选项：class_name和：foreign_key将被忽略，因为关联使用源反射。您只能通过联接模型上的has_one或belongs_to关联使用：through查询。

这告诉我的是，除了订阅模型（我的连接模型）之外，你不能使用：on on has_one。吮！如果有人有任何其他答案，那将是伟大的。

通过has_one：through访问belongs_to关联模型

2 个答案: