Linq to Entities Join, Group, Sum with Northwind Orders答案

【问题标题】：Linq to Entities Join, Group, Sum with Northwind OrdersLinq to Entities Join, Group, Sum with Northwind Orders
【发布时间】：2018-07-17 13:33:27
【问题描述】：

我正在尝试编写一个 linq 查询，它应该对 Northwind.mdb 中的 order_detail 行求和，然后返回汇总的总数以及负责员工的一些详细信息。我正在使用 LINQpad 对其进行测试，这就是我目前所拥有的

void Main()
{
    var result = (from e in Employees
        join o in Orders on e.EmployeeID equals o.EmployeeID
        join d in OrderDetails on o.OrderID equals d.OrderID
        where o.OrderID == 10250
        group new { e, o, d } by new 
        {
             o.OrderID, e.Address, e.BirthDate, e.City, e.Country,
             e.LastName, e.FirstName, e.Title, e.TitleOfCourtesy, e.HireDate,
             e.Region, e.PostalCode, e.HomePhone,
             e.Extension, e.ReportsTo,e.PhotoPath, e.EmployeeID,
             d.Quantity, d.UnitPrice, d.Discount
        }
        into grp select new   
        {
            Name = grp.Key.FirstName + " " + grp.Key.LastName,
            OrderID = grp.Key.OrderID,      
            Address = grp.Key.Address,
            SalesTotal = grp.Sum(x => x.d.UnitPrice * x.d.Quantity)
        });

        result.Dump();       
}

Output from LINQPad

我只期待一行，总共 1813.00。谁能告诉我我做错了什么？

【问题讨论】：

标签： c# linq linqpad

【解决方案1】：

您没有在正确的级别进行分组。如果您将其更改为按员工分组，那么您应该得到正确的结果：

void Main()
{
    var result = (from e in Employees
        join o in Orders on e.EmployeeID equals o.EmployeeID
        join d in OrderDetails on o.OrderID equals d.OrderID
        where o.OrderID == 10250
        group new { e, o, d } by new 
        {
             e.EmployeeID, e.FirstName, e.LastName, e.Address
        }
        into grp select new   
        {
            Name = grp.Key.FirstName + " " + grp.Key.LastName,
            Address = grp.Key.Address,
            SalesTotal = grp.Sum(x => x.d.UnitPrice * x.d.Quantity)
        });

        result.Dump();       
}

如果您希望每个订单有一行，也可以按此分组：

void Main()
{
    var result = (from e in Employees
        join o in Orders on e.EmployeeID equals o.EmployeeID
        join d in OrderDetails on o.OrderID equals d.OrderID
        where o.OrderID == 10250
        group new { e, o, d } by new 
        {
             e.EmployeeID, e.FirstName, e.LastName, e.Address,
             o.OrderID
        }
        into grp select new   
        {
            Name = grp.Key.FirstName + " " + grp.Key.LastName,
            OrderID = grp.Key.OrderID,
            Address = grp.Key.Address,
            SalesTotal = grp.Sum(x => x.d.UnitPrice * x.d.Quantity)
        });

        result.Dump();       
}

【讨论】：