has_one ：条件被解释为属性？

Question

这个协会：

class Business < ActiveRecord::Base
  has_one    :map_address, :as=>:addressable, :class_name => 'Address', :conditions => {'addresses.map_address'=>true}, :dependent => :destroy
end

导致此错误：

ruby-1.8.7-p334 :005 > n = Business.new
ruby-1.8.7-p334 :006 > n.build_map_address
ActiveRecord::UnknownAttributeError: unknown attribute: addresses.map_address

用来读取的代码

:conditions => {:map_address=>true}

但缺少表名会导致查找时出现此问题（它将字段名放在错误的表上）：

ActiveRecord::StatementInvalid (PGError: ERROR:  column counties.map_address does not exist
                                                             ^
SELECT "businesses".* FROM "businesses"   INNER JOIN "addresses" ON ("businesses"."id" = "addresses"."addressable_id" AND "addresses"."addressable_type" = 'Business')  INNER JOIN "counties" ON ("counties"."id" = "addresses"."county_id") AND counties."map_address" IS NULL  WHERE (counties.id = 23)  ORDER BY businesses.updated_at DESC):

这个选项：

"adresses.map_address is true"

在查找时产生此错误：

PGError: ERROR:  missing FROM-clause entry for table "adresses"
LINE 1: ..." ON ("states"."id" = "addresses"."state_id") AND adresses.m...
                                                             ^
: SELECT "businesses".* FROM "businesses"   INNER JOIN "addresses" ON ("businesses"."id" = "addresses"."addressable_id" AND "addresses"."addressable_type" = 'Business')  INNER JOIN "states" ON ("states"."id" = "addresses"."state_id") AND adresses.map_address is NULL  WHERE (states.id = 4)  ORDER BY businesses.updated_at DESC

所以我的问题是为什么 rails 会试图将这种情况转化为属性？我怎样才能让它双向工作？我的猜测是 rails 正在尝试将条件设置为新记录的默认值。

Answer 1

为什么不

has_one    :map_address, :as=>:addressable, :class_name => 'Address', :conditions => {:map_address => true}, :dependent => :destroy

Answer 2

map_attribute 是一个字段吗？在这种情况下会出现错误，因为您有addresses.map_address，但是您在谈论什么地址对象？通过写地址你不是指一个特定的地址
换句话说，Map_address 似乎是一个对象的属性，所以 object1 有它的 map_address，object2 有它的 map_address，但是当你输入地址时，你不是指任何对象，并导致错误。