has_many 关系的finder_sql

Question

给定以下两个（简化的）模型：

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，这似乎工作得很好：

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

但是当我尝试跟随我得到一个mysql错误：

>> 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'

所以，Rails 正在生成一个无效的 SQL 语句。原因可能是我的finder_sql，因为没有finder_sql的关联按预期工作。

我已经尝试删除所有可选插件 (will_paginate)。我想要实现的事情其实很简单：在我的关联中包含所有符合条件(users.customer_id = 1 OR users.customer_id IS NULL) 的用户模型。

感谢任何帮助！

Answer 1

如果你真的有一个特殊的“全球”客户，你可能会发现它更容易，这样你就不需要处理 NULL 的尴尬。

这是使用Null Object pattern 的示例。

Answer 2

这些都应该工作

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"}