Question

我正在尝试收集一些发票，这些发票不属于尚未完成的借记卡。

因此，对于每张发票，不存在未完成的借记因此，没有借方的发票或只有完成的借方的发票都是有效的

Invoice通过联合模型InvoiceDebit

与借方有一个has_many关系

class Invoice < ActiveRecord::Base
   has_many :debit_invoices
   has_many :debits, :through => :debit_invoices
end

class DebitInvoice < ActiveRecord::Base
   belongs_to :invoice
   belongs_to :debit
end

class Debit < ActiveRecord::Base
   attr_accessible :completed

   has_many :debit_invoices
   has_many :invoices, :through => :debit_invoices
end

我宁愿不在SQL中写出整个查询，因为我已经使用AREL来限制当前登录用户的发票池。

Answer 1

您可以将高效的where子句构造为SQL片段。

def does_not_have_an_incomplete_debit
  self.where("not exists
               (select null
                  from debit_invoices di
                  join debits         d on d.id = di.debit_id
                 where di.invoice_id = invoices.id and
                       d.completed   = false)")
end

然后：

Invoices.for_current_user(current_usser.id).does_not_have_an_incomplete_debit.all

Rails关联：通过NOT EXIST

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