ruby-on-rails - 在 rails 中用 has_many 计数

Question

我有一个Order 和Orderdetails

Orderdetails belongs_to Order

Order has_many Orderdetails

我正在尝试将以下查询转换为 ActiveRecord count 函数

select Count(*) 
from orderdetails A, orders B 
where A.prodid='6' and A.orderid= B.id and B.custid='11'

我试过:

@count = Orderdetail.count(:conditions => "prodid = 6 and order.custid = 11")

然而，这给出了错误:

PGError: ERROR:  syntax error at or near "order"
LINE 1: ...unt_all FROM "orderdetails" WHERE (prodid = 6 and order.cust...

编辑我改为订购s

但现在我得到这个错误:

ActiveRecord::StatementInvalid: PGError: ERROR: missing FROM-clause entry for table "orders" LINE 1: ...unt_all FROM "orderdetails" WHERE (prodid = 6 and orders.cus...

Answer 1

您需要添加 :joins => :order'，因为您的条件包含订单表中的元素(这就是为什么您会收到错误 missing FROM-clause)，尝试:

@count = Orderdetail.count(:joins => :order, :conditions => "prodid = 6 and orders.custid = 11")

在条件下使用数组也更好(更安全):

@count = Orderdetail.count(:joins => :order, :conditions => ["prodid = ? and orders.custid = ?", 6, 11])