LINQ Sum与GroupBy

Question

（不确定我是否需要GroupBy）

我的（简化）表：

Products（ProductID，Name，Code）
Invoices（InvoiceID，Number，IsPaid）
Invoices_Products（InvoiceID，ProductID，Quantity，Price） - 多对多链接表

我需要显示按产品代码分组的付款发票的发票_产品列表（数量*价格）。

我首先用来获取可以绑定到UI的集合的代码：

IEnumerable<Invoices_Products> invoices_products = db.Invoices_Products
.Where(ip => ip.Invoice.IsPaid).DistinctBy(m => m.Product.Code);

然后我遍历这个以将其绑定到UI：

List<BindableInvoiceProduct> bindableInvoiceProducts = 
new List<BindableInvoiceProduct>();

foreach (var item in invoices_products)
{
    decimal salesValue = db.Invoices_Products.Where(ip => ip.Invoice.IsPaid 
    && ip.Product.Code == item.Product.Code).Sum(m => (m.Price * m.Quantity));

    bindableInvoiceProducts.Add(new BindableInvoiceProduct()
    {
        A = item.A,
        B = item.B,
        SalesValue = salesValue.ToString()
    });
}

（来自morelinq的DistinctBy方法）

为什么这不完全正确？

编辑

一些数据：

产品 - ProductID = 1，Name = 123，Code = A
产品 - ProductID = 2，Name = 456，Code = A
发票 - InvoiceID = 1，Number = INV123，IsPaid = True
发票_产品 - InvoiceID = 1，ProductID = 1，数量= 10，价格= 100
Invoices_Products - InvoiceID = 1，ProductID = 2，Quantity = 10，Price = 200

预期结果：

代码= A，SalesValue = 3000

Answer 1

from invoice in invoices
where invoice.IsPaid
from xr in invoice.InvoiceProducts
group xr.Quantity * xr.Price by xr.Product.Code into g
select new {Code = g.Key, SalesValue = g.Sum()};

如果您想要每张发票，那么：

from invoice in invoices
where invoice.IsPaid
from xr in invoice.InvoiceProducts
group xr.Quantity * xr.Price
  by new {Code = xr.Product.Code, Invoice = invoice }
  into g
select new {
  Code = g.Key.Code,
  Invoice = g.Key.Invoice,
  SalesValue = g.Sum()};

Answer 2

根据您的描述，我会写：

var bindableInvoiceProducts = db.Invoices_Products
    .Where(ip => ip.Invoice.IsPaid)
    .GroupBy(ip => ip.Product.Code, 
             (code, ips) => new BindableInvoiceProduct()
                {
                    Code = code,
                    SalesValue = ips.Sum(ip => (ip.Price*ip.Quantity))
                })
    .ToList();

那是你需要的吗？您的代码中的item.A和item.B是什么？