多表发票SUM比较

Question

假设我在rails应用程序中有3个表：

发票

id  | customer_id  | employee_id  | notes
---------------------------------------------------------------
1   | 1            | 5            | An order with 2 items.
2   | 12           | 5            | An order with 1 item.
3   | 17           | 12           | An empty order.
4   | 17           | 12           | A brand new order.

invoice_items

id  | invoice_id  | price  | name
---------------------------------------------------------
1   | 1           | 5.35   | widget
2   | 1           | 7.25   | thingy
3   | 2           | 1.25   | smaller thingy
4   | 2           | 1.25   | another smaller thingy

invoice_payments

id  | invoice_id  | amount  | method      | notes
---------------------------------------------------------
1   | 1           | 4.85    | credit card | Not enough 
2   | 1           | 1.25    | credit card | Still not enough
3   | 2           | 1.25    | check       | Paid in full

这代表4个订单：

第一项有2项，总计12.60项。它有两笔付款，总付款金额为6.10。此订单已部分支付。

第二项只有一项，一项付款，总计1.25。此订单全额支付。

第三个订单没有物品或付款。这对我们很重要，有时我们会使用这种情况。它被认为是全额付款。

最终订单再次有一个项目，共计1.25，但尚未付款。

现在我需要一个查询：

告诉我所有未完全支付的订单;也就是说，所有订单都使得项目总数大于付款总额。

我可以在纯sql中做到这一点：

SELECT      invoices.*,
            invoice_payment_amounts.amount_paid AS amount_paid,
            invoice_item_amounts.total_amount AS total_amount
FROM        invoices
LEFT JOIN   (
                SELECT      invoices.id AS invoice_id,
                            COALESCE(SUM(invoice_payments.amount), 0) AS amount_paid
                FROM        invoices
                LEFT JOIN   invoice_payments
                ON          invoices.id = invoice_payments.invoice_id
                GROUP BY    invoices.id
            ) AS invoice_payment_amounts
ON          invoices.id = invoice_payment_amounts.invoice_id
LEFT JOIN   (
                SELECT      invoices.id AS invoice_id,
                            COALESCE(SUM(invoice_items.item_price), 0) AS total_amount
                FROM        invoices
                LEFT JOIN   invoice_items
                ON          invoices.id = invoice_items.invoice_id
                GROUP BY    invoices.id
            ) AS invoice_item_amounts
ON          invoices.id = invoice_item_amounts.invoice_id
WHERE       amount_paid < total_amount

但是......现在我需要把它变成rails（可能作为范围）。我可以使用find_by_sql，但然后返回一个数组，而不是ActiveRecord :: Relation，这不是我需要的，因为我想将它与其他范围链接（例如，有一个过期的范围，它使用这个）等

所以原始SQL可能不是正确的方式去这里.....但是什么是？我无法在activerecord的查询语言中执行此操作。

我到目前为止最接近的是：

Invoice.select('invoices.*, SUM(invoice_items.price) AS total, SUM(invoice_payments.amount) AS amount_paid').
  joins(:invoice_payments, :invoice_items).
  group('invoices.id').
  where('amount_paid < total')

但是失败了，因为在＃1这样的订单上，多次付款，它错误地使订单的价格加倍（由于多次加入），显示它仍然是无偿的。我在SQL中遇到了同样的问题，这就是我按照我的方式构建它的原因。

这有什么想法？

Answer 1

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