finder_sql爲的has_many關係

Question

鑑於以下兩個（簡體）型號：

class Customer < ActiveRecord::Base 
    # finder sql to include global users in the association 
    has_many :users, :dependent => :destroy, 
    :finder_sql => 'SELECT `u`.* FROM `users` `u` 
    WHERE (`u`.`customer_id` = "#{id}" OR `u`.`customer_id` IS NULL)' 

    validates_presence_of :name 
end 

class User < ActiveRecord::Base 
    # most users belong to a customer. 
    # however, the customer_id may be NULL 
    # to implement the concept of "global" users. 
    belongs_to :customer 
    validates_presence_of :email 
end 

起初，這似乎只是很好地工作：

>> Customer.first.users # => Array of users including global users 

但是當我嘗試下我得到一個MySQL錯誤：

>> Customer.first.users.find_by_email("test@example.com") 
ActiveRecord::StatementInvalid: Mysql::Error: Operand should contain 1 column(s): 
SELECT * FROM `users` 
WHERE (`users`.`email` = 'test@example.com') AND 
(
    SELECT `u`.* FROM `users` `u` 
    WHERE (`u`.`customer_id` = "1" OR `u`.`customer_id` IS NULL) 
    ORDER BY u.nickname 
) LIMIT 1 
from /Library/Ruby/Gems/1.8/gems/activerecord-2.2.2/lib/active_record/connection_adapters/abstract_adapter.rb:188:in `log' 
from /Library/Ruby/Gems/1.8/gems/activerecord-2.2.2/lib/active_record/connection_adapters/mysql_adapter.rb:309:in `execute' 
from /Library/Ruby/Gems/1.8/gems/activerecord-2.2.2/lib/active_record/connection_adapters/mysql_adapter.rb:563:in `select' 
from /Library/Ruby/Gems/1.8/gems/activerecord-2.2.2/lib/active_record/connection_adapters/abstract/database_statements.rb:7:in `select_all_without_query_cache' 
from /Library/Ruby/Gems/1.8/gems/activerecord-2.2.2/lib/active_record/connection_adapters/abstract/query_cache.rb:62:in `select_all' 
from /Library/Ruby/Gems/1.8/gems/activerecord-2.2.2/lib/active_record/base.rb:635:in `find_by_sql' 
from /Library/Ruby/Gems/1.8/gems/activerecord-2.2.2/lib/active_record/base.rb:1490:in `find_every' 
from /Library/Ruby/Gems/1.8/gems/activerecord-2.2.2/lib/active_record/base.rb:1452:in `find_initial' 
from /Library/Ruby/Gems/1.8/gems/activerecord-2.2.2/lib/active_record/base.rb:587:in `find' 
from /Library/Ruby/Gems/1.8/gems/activerecord-2.2.2/lib/active_record/base.rb:1812:in `find_by_email' 
from /Library/Ruby/Gems/1.8/gems/activerecord-2.2.2/lib/active_record/base.rb:1800:in `send' 
from /Library/Ruby/Gems/1.8/gems/activerecord-2.2.2/lib/active_record/base.rb:1800:in `method_missing' 
from /Library/Ruby/Gems/1.8/gems/activerecord-2.2.2/lib/active_record/associations/association_collection.rb:370:in `send' 
from /Library/Ruby/Gems/1.8/gems/activerecord-2.2.2/lib/active_record/associations/association_collection.rb:370:in `method_missing' 
from /Library/Ruby/Gems/1.8/gems/activerecord-2.2.2/lib/active_record/base.rb:2003:in `with_scope' 
from /Library/Ruby/Gems/1.8/gems/activerecord-2.2.2/lib/active_record/associations/association_proxy.rb:202:in `send' 
from /Library/Ruby/Gems/1.8/gems/activerecord-2.2.2/lib/active_record/associations/association_proxy.rb:202:in `with_scope' 
from /Library/Ruby/Gems/1.8/gems/activerecord-2.2.2/lib/active_record/associations/association_collection.rb:366:in `method_missing' 

因此，Rails正在生成無效的SQL語句。原因可能是我的finder_sql，因爲沒有finder_sql的關聯按預期工作。

我已經嘗試刪除所有可選插件（will_paginate）。我試圖實現的事情其實很簡單：在我的關聯中包含與以下條件(users.customer_id = 1 OR users.customer_id IS NULL)匹配的所有用戶模型。

感謝任何幫助！

Answer 1

這些要麼應該工作

User.find(:all, :conditions => ['customer_id = ? OR customer_id IS NULL', Customer.first[:id]]) 

或

Customer.first.users.select{|user| user.email == "test@example.com"} 

Answer 2

您可能會發現更容易，如果你確實有一個特殊的「全球性」的客戶，所以你並不需要處理的尷尬的NULL。

這是使用Null Object pattern的示例。