在LINQ选择结果中添加计算字段？

Question

我有一个LINQ查询（使用EF）

基本上我想根据另一列的值在Select结果中添加一列。

我在数据库表中有PaymentDate列，但没有Paid列。如果PaymentDate列中存在空，则还会显示付款为false，如果其中包含某个日期，则表示已付款为真。

这是我的疑问，请指导我如何做到这一点。

 var selectedResults=
    from InvoiceSet in Invoices
    join BookedAreasSet in BookedAreas 
    on InvoiceSet.InvoiceID equals BookedAreasSet.InvoiceID
    join AreaSet in Areas on BookedAreasSet.AreaID equals AreaSet.AreaID
    select new     {InvoiceSet.InvoiceNumber,InvoiceSet.Amount,InvoiceSet.TotalDiscount,InvoiceSet.GST,       InvoiceSet.PaymentDate,InvoiceSet.ShoppingCentreID,BookedAreasSet.BookedAreaID,
AreaSet.Name,Here I want to add calculated value column based on InvoiceSet.PaymentDate value}

Answer 1

我认为你应该可以做这样的事情

var selectedResults=
    from InvoiceSet in Invoices
    join BookedAreasSet in BookedAreas 
    on InvoiceSet.InvoiceID equals BookedAreasSet.InvoiceID
    join AreaSet in Areas on BookedAreasSet.AreaID equals AreaSet.AreaID
    select new { InvoiceSet.InvoiceNumber,InvoiceSet.Amount,InvoiceSet.TotalDiscount,InvoiceSet.GST,       
        InvoiceSet.PaymentDate,InvoiceSet.ShoppingCentreID,BookedAreasSet.BookedAreaID,
        AreaSet.Name,Paid = (InvoiceSet.PaymentDate == null) }