元搜索 has_many 其中所有/无必须匹配
我正在尝试进行元搜索或范围，为我提供所有不具有任何 has_many 关联等于 type == “Something” 的对象。
示例：
class Order < ActiveRecord::Base
has_many :billing_base
end
class InvoiceBase < ActiveRecord::Base
belongs_to :order
end
class Invoice < InvoiceBase
end
class OrderAcknowledgement < InvoiceBase
end
搜索有发票的订单可以通过自定义范围轻松完成：
joins(:invoice_base).where(:invoice_base => {:type => "Invoice"})
或元搜索：
:invoice_base_type_equals => "Invoice"
现在我该如何做相反的事情，找到没有发票的订单？ （应始终允许订单确认）
Im trying to make a metasearch or alternatively a scope that gives me all objects that doesnt have any of its has_many-association equal to type == "Something".
Example:
class Order < ActiveRecord::Base
has_many :billing_base
end
class InvoiceBase < ActiveRecord::Base
belongs_to :order
end
class Invoice < InvoiceBase
end
class OrderAcknowledgement < InvoiceBase
end
Searching for orders that have an invoice is easily done by a custom scope:
joins(:invoice_base).where(:invoice_base => {:type => "Invoice"})
or metasearch:
:invoice_base_type_equals => "Invoice"
Now how do I do the opposite, find orders that have NO invoice? (OrderAcknowledgements should always be allowed)
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当试图在我的计算机上解决这个问题时，我最终编写了一条涉及子查询的 sql 语句。我想知道您是否可以将原始 SQL 填充到 where 方法中。
我在我的网站上尝试了一下，似乎有效。请注意，我使用的是 MySQL
When trying to figure this out on my computer, i ended up writing a sql statement that involves a subquery. I wonder if maybe you can populate the raw SQL into the where method.
I gave this a try on my site and it seemed to work. Note that I am using MySQL