在实体框架中通过SQL GROUP BY语句执行GROUP BY查询

Question

I am writing an invoicing system in VB.NET and ASP.NET using Entity Framework to store my objects. I want to sum up all of the billable line items for any specific month and have them collated into an invoice. The following SQL query accomplishes this, however I can't get it working in Entity Framework code-first:

SQL query:

SELECT DISTINCT 
    [database].[dbo].[WorkOrderDetails].PriceCodeID,
    [database].[dbo].[WorkOrderDetails].[Description],
    SUM([database].[dbo].[WorkOrderDetails].[Quantity]) AS [Quantity],
    SUM([Subtotal]) AS Subtotal,
    SUM([Total]) AS Total
FROM 
    [database].[dbo].[WorkOrderDetails] 
INNER JOIN 
    [database].[dbo].[WorkOrders] ON [database].[dbo].[WorkOrderDetails].[WorkOrderID] = [database].[dbo].[WorkOrders].[WorkOrderID]
WHERE 
    [ClientID] = 182 
    AND [WorkOrders].[Date] >= '10/1/2016' 
    AND [WorkOrders].[Date] < '10/31/2016' 
GROUP BY 
    [PriceCodeID], [Description]

The output of this query is similar to the following:

PriceCodeID | Description | Quantity | Subtotal | Total  
------------+-------------+----------+----------+--------
26            BOX REFILE        19         47.50    47.50
28            BOX RETRIEVAL     15         37.50    37.50
98            Del/Pu Out       376        545.20   545.20
95            Shredding      16893        760.19   760.19

My objects are:

• WorkOrder : WorkOrderID, Date, ClientID (foreign key) , List (of WorkOrderDetail )

• WorkOrderDetail : WorkOrderDetailID, PriceCodeID (foreign key) , Description, UnitPrice, Quantity, Subtotal, Tax, Total, WorkOrderID (foreign key)

• PriceCode : PriceCodeID, ShortCode, Description, UnitPrice, Tax

I'm attempting to use the statement below, but I'm unsure how to use the GroupBy statement.

newInvoice.Details = _db.WorkOrderDetails
                        .Include("WorkOrder")
                        .Where(Function(wod) wod.WorkOrder.Date >= newInvoice.StartDate And 
                                             wod.WorkOrder.Date < newInvoice.EndDate And 
                                             wod.WorkOrder.ClientID = newInvoice.ClientID)
                        .GroupBy(...)
                        .ToList()

Answer 1

You can get the aggregated results by

Dim aggregate = From wod in _db.WorkOrderDetails
                Where wod.WorkOrder.Date >= newInvoice.StartDate And 
                      wod.WorkOrder.Date < newInvoice.EndDate And 
                      wod.WorkOrder.ClientID = newInvoice.ClientID)
                Group wod By Key = New With { Key wod.PriceCodeID, Key Description }
                Into Group
                Select agg = Key.PriceCodeID,
                             Key.Description,
                             Quantity = Group.Sum(Function(wod) wod.Quantity),
                             Subtotal = Group.Sum(Function(wod) wod.Subtotal),
                             Total = Group.Sum(Function(wod) wod.Total)

You can't directly create new WorkOrderDetail in this query, because EF doesn't allow creating new entity types in a LINQ query. But you can use aggregate.AsEnumerable() to continue:

newInvoice.Details = aggregate.AsEnumerable()
                     .Select(Function (wod) New WorkOrderDetail ...)