如何在entity framework查询中使用左连接？

我正在使用entity framework4.5。 我必须将SQL查询转换为实体查询：

SELECT Customer.CustCode, Invoice.InvoiceId, Invoice.BatchNumber, Invoice.InvoiceDate, Invoice.AdjustFlag, Invoice.InvoiceAmount, Invoice.InvoiceNote, Invoice.AmountPaid, Customer.BillingContact, Customer.BillingCompany, Customer.BillingStreet1, Customer.BillingStreet2, Customer.BillingCity, Customer.BillingState, Customer.BillingZip, [Order].PickupDate, [Order].OrderNumber, [Order].OrderTotal, [Order].ProNumber, [Order].PickupCompany, [Order].PickupCity, [Order].PickUpState, [Order].Dcompany, [Order].Dcity, [Order].Dstate, CONVERT(varchar(5), DeliverInTime, 114) AS DelInTime, [Order].PiecesWeight1, [Order].BaseRATE, [Order].POD, [Order].Requester, [Order].Po1, [Order].Po2, AccessorialCharge.Description, OrderDriverExtraCharge.AccessorialChargeDesc, OrderDriverExtraCharge.AccessorialChargeAmount, [Order].NormalDiscount, - 1 * [Order].DISCAmount AS DISCAmount FROM (((Invoice INNER JOIN [Order] ON Invoice.InvoiceId = [Order].InvoiceId) INNER JOIN Customer ON Invoice.CustID = Customer.CustID) LEFT JOIN OrderDriverExtraCharge ON [Order].OrderNumberId = OrderDriverExtraCharge.OrderNumberId) LEFT JOIN AccessorialCharge ON OrderDriverExtraCharge.AccessorialChargeId = AccessorialCharge.AccessorialChargeId where Invoice.InvoiceId = '1117782' 

如果我更改OrderDriverExtraCharge.OrderNumberId) LEFT JOIN到OrderDriverExtraCharge.OrderNumberId) JOIN （简单连接）或内连接它没有显示正确的结果。

我试过这个：

 from I in db.Invoices join O in db.Orders on I.InvoiceId equals O.InvoiceId join C in db.Customers on I.CustId equals C.CustId join OD in db.OrderDriverExtraCharges on O.OrderNumberId equals OD.OrderNumberId join AC in db.AccessorialCharges on OD.AccessorialChargeId equals AC.AccessorialChargeId where I.InvoiceId == invoice.InvoiceId select new PrintInvoiceViewModel() 

但它没有显示所需的结果。 请帮助我，如果它适合我​​，我会标记你的答案。 谢谢。

Answer 1

你可以这样做：

 from I in db.Invoices join O in db.Orders on I.InvoiceId equals O.InvoiceId join C in db.Customers on I.CustId equals C.CustId from OD in db.OrderDriverExtraCharges .Where(w=>w.OrderNumberId==O.OrderNumberId).DefaultIfEmpty() from AC in db.AccessorialCharges .Where(w=>w.AccessorialChargeId==OD.AccessorialChargeId).DefaultIfEmpty() where I.InvoiceId == invoice.InvoiceId select new PrintInvoiceViewModel() 

Answer 2

您应该使用DefaultIfEmpty方法，该方法返回IEnumerable的元素，或者如果序列为空则返回默认值的单例集合：

 from I in db.Invoices join O in db.Orders on I.InvoiceId equals O.InvoiceId join C in db.Customers on I.CustId equals C.CustId join OD in db.OrderDriverExtraCharges on O.OrderNumberId equals OD.OrderNumberId into ODs from OD in ODs.DefaultIfEmpty() join AC in db.AccessorialCharges on OD.AccessorialChargeId equals AC.AccessorialChargeId into ACs from AS in ACs.DefaultIfEmpty() where I.InvoiceId == invoice.InvoiceId select new PrintInvoiceViewModel()