我正在尝试将SQL查询转换为lambda表达式。
SQL查询如下所示：
select
po.OrderID as order_number,
pc.emailaddress as user_email,
pc.CustomerID as customer_code,
pb.DisplayName as bank,
poab.street1 + ' ' + poab.Street2 as 'billing_address',
po.createdate as 'created_date',
'tr' as currency,
po.TotalPrice - po.TotalPromotionPrice as discount_amount,
null as 'extra_field',
pbi.InstalmentCount as installment_count,
pp.DisplayName as payment_type,
poas.street1 + ' ' + poas.street2 as 'shipping_address',
'UPS' as shipping_company,
pos.Displayname as status,
po.ShipmentReferenceNo as 'tracking_number'
from
PrmOrder po
inner join
prmcustomer pc on po.CustomerID = pc.customerid
inner join
PrmBank pb on po.BankId = pb.BankId
inner join
prmorderaddress poab on po.orderid = poab.orderid and poab.isbillingaddress = 1
left join
PrmBankInstalment pbi on pbi.BankInstalmentID = po.BankInstalmentID
inner join
PrmPaymentType pp on po.PaymentTypeID = pp.PaymentTypeId
inner join
prmorderaddress poas on po.orderid = poas.orderid and poas.isshippingaddress = 1
inner join
prmorderstatus pos on po.orderstatusid = pos.orderstatusid
由于这两个表之间的一对多连接以及我需要显示两条线，我内部加入了同一个表两次。基本上，OrderID可以在OrderAddress表上有两个记录，一个用于记帐地址，另一个用于发货地址。它在SQL上运行良好但我无法将其转换为lambda表达式。
我先尝试过这样的事情;
var OrderHeader = db.PrmOrders
.Include(x => x.PrmCustomer)
.Include(x => x.PrmBank)
.Include(x => x.PrmOrderAddresses)
.Include(x => x.PrmBankInstalment)
.Include(x => x.PrmPaymentType)
.Include(x => x.PrmOrderStatu)
.Where(x => x.PrmCustomer.EmailAddress != null && x.OrderStatusID != 1 && x.OrderID > OrderID)
.OrderBy(x => x.OrderID)
.Select(x => new HeaderDTO()
{
order_number = x.OrderID,
user_email = x.PrmCustomer.EmailAddress,
customer_code = x.PrmCustomer.CustomerID,
order_amount = x.GrandTotal,
bank = x.PrmBank.DisplayName,
billing_address = x.PrmOrderAddresses
.Where(c => c.IsBillingAddress == true && c.OrderID == x.OrderID)
.Select(c => c.Street1 + " " + c.Street2).ToString(),
created_date = x.OrderDate,
currency = "TRY",
discount_amount = x.TotalPrice - x.TotalPromotionPrice,
installment_count = x.PrmBankInstalment.InstalmentCount == null ? 0 : x.PrmBankInstalment.InstalmentCount,
payment_type = x.PrmPaymentType.DisplayName,
shipping_address = x.PrmOrderAddresses
.Where(c => c.IsShippingAddress == true & c.OrderID == x.OrderID)
.Select(c => c.Street1 + " " + c.Street2 + " " + c.PrmAddressCity.DisplayName + " " + c.PrmAddressCountry.DisplayName).ToString(),
shipping_company = "UPS",
status = x.PrmOrderStatu.DisplayName,
tracking_number = x.ShipmentReferenceNo == null ? "" : x.ShipmentReferenceNo
});
这导致V alues of type 'collection[Edm.String(Nullable=True,DefaultValue=,MaxLength=,Unicode=,FixedLength=)]' can not be converted to string.错误，并且Edmx中的删除/重新添加表不起作用，如建议的那样。
所以现在我正在尝试使用Lambda表达式进行三重连接，它感觉不太正常，看起来有点混乱
var OrderHeader = db.PrmOrders
.Include(x => x.PrmCustomer)
.Include(x => x.PrmBank)
.Include(x => x.PrmOrderAddresses)
.Include(x => x.PrmBankInstalment)
.Include(x => x.PrmPaymentType)
.Include(x => x.PrmOrderStatu)
.Where(x => x.PrmCustomer.EmailAddress != null && x.OrderStatusID != 1 && x.OrderID > OrderID)
.OrderBy(x => x.OrderID)
.Join(db.PrmOrderAddresses.Where(a => a.IsBillingAddress == true), x => x.OrderID, a => a.OrderID, (x, a) => new
{
BillingAddress = a.Street1 + " " + a.Street2 + " " + a.PrmAddressCity.DisplayName + " " + a.PrmAddressCountry.DisplayName,
OrderID = x.OrderID
})
.Join(db.PrmOrderAddresses.Where(a => a.IsShippingAddress == true), x => x.OrderID, s => s.OrderID, (x, s) => new
{
order_number = x.OrderID,
user_email = x.PrmCustomer.EmailAddress,
customer_code = x.PrmCustomer.CustomerID,
order_amount = x.GrandTotal,
bank = x.PrmBank.DisplayName,
//billing_address = x.PrmOrderAddresses
// .Where(c => c.IsBillingAddress == true && c.OrderID == x.OrderID)
// .Select(c => c.Street1 + " " + c.Street2).ToString(),
created_date = x.OrderDate,
currency = "TRY",
discount_amount = x.TotalPrice - x.TotalPromotionPrice,
installment_count = x.PrmBankInstalment.InstalmentCount == null ? 0 : x.PrmBankInstalment.InstalmentCount,
payment_type = x.PrmPaymentType.DisplayName,
//shipping_address = x.PrmOrderAddresses
// .Where(c => c.IsShippingAddress == true & c.OrderID == x.OrderID)
// .Select(c => c.Street1 + " " + c.Street2 + " " + c.PrmAddressCity.DisplayName + " " + c.PrmAddressCountry.DisplayName).ToString(),
shipping_company = "UPS",
status = x.PrmOrderStatu.DisplayName,
tracking_number = x.ShipmentReferenceNo == null ? "" : x.ShipmentReferenceNo
ShippingAddress = s.Street1 + " " + s.Street2 + " " + s.PrmAddressCity.DisplayName + " " + s.PrmAddressCountry.DisplayName
});
我如何实现我的目标？
答案 0 :(得分：2)
正如错误消息告诉您的那样，您无法将表达式转换为字符串，它没有任何意义。
如果有多个项目，您必须决定使用First / FirstOrDefault，如果总是有一个项目，则需要var OrderHeader = db.PrmOrders
.Where(x => x.PrmCustomer.EmailAddress != null && x.OrderStatusID != 1 && x.OrderID > OrderID)
.OrderBy(x => x.OrderID)
.Select(x => new HeaderDTO
{
order_number = x.OrderID,
user_email = x.PrmCustomer.EmailAddress,
customer_code = x.PrmCustomer.CustomerID,
order_amount = x.GrandTotal,
bank = x.PrmBank.DisplayName,
billing_address = x.PrmOrderAddresses
.Where(c => c.IsBillingAddress && c.OrderID == x.OrderID)
.Select(c => c.Street1 + " " + c.Street2)
.ToList() / .First() / .FirstOrDefault(),
created_date = x.OrderDate,
currency = "TRY",
discount_amount = x.TotalPrice - x.TotalPromotionPrice,
installment_count = x.PrmBankInstalment.InstalmentCount == null ? 0 : x.PrmBankInstalment.InstalmentCount,
payment_type = x.PrmPaymentType.DisplayName,
shipping_address = x.PrmOrderAddresses
.Where(c => c.IsShippingAddress && c.OrderID == x.OrderID)
.Select(c => c.Street1 + " " + c.Street2 + " " + c.PrmAddressCity.DisplayName + " " + c.PrmAddressCountry.DisplayName)
.ToList() / .First() / .FirstOrDefault(),
shipping_company = "UPS",
status = x.PrmOrderStatu.DisplayName,
tracking_number = x.ShipmentReferenceNo == null ? "" : x.ShipmentReferenceNo
});
;如果没有项目，则需要>> xmlread()
warning: the 'xmlread' function is not yet implemented in Octave
Please read <http://www.octave.org/missing.html> to learn how you can
contribute missing functionality.
error: 'xmlread' undefined near line 1 column 1
：
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