最后,不支持LastOrDefault [英] Last and LastOrDefault not supported
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问题描述
我试图让在列表中的第一个值和最终值。查询操作符一()
是支持的,但末()
和 LastOrDefault()
给出错误。我使用了末()
运营商在不正确的方式。
VAR purchaseBills = db.PurchaseBills.Where(
P => p.BillDate> = DateTime.Now.Date和放大器;&安培;
p.BillDate< DateTime.Now.AddDays(1).Date&安培;&安培;
!(布尔)p.IsDeleted).OrderBy(P => p.BillID);
如果(purchaseBills.Count()大于0)
{
变种firstBill = purchaseBills.First(); //这是支持
//尝试1
变种lastBill = purchaseBills.Last(); // 不支持
//尝试2
变种lastBill = purchaseBills.LastOrDefault(); //不支持
//尝试3
VAR lastBill = purchaseBills.Reverse()一()。 //不支持
textBoxPurchaseBillFrom.Text = firstBill.BillNo.ToString();
textBoxPurchaseBillTo.Text = lastBill.BillNo.ToString();
}
更新: --errors -
尝试1:查询运算符'最后'不支持
尝试2:不支持查询运算符LastOrDefault
尝试3:不支持查询运算符反向
解决方案
- 而不是把它变成自己的名单通过调用
了ToList()
或的ToArray()
我想preFER使用AsEnumerable()
。 - 此外像其他人一样,你应该尝试
OrderByDescending()
- 而不是
计数()
我会用任何()
。
I am trying to get the First value in the list and the last value. The query operator First()
is supported but Last()
and LastOrDefault()
gives error. Am I using the Last()
operator in incorrect manner.
var purchaseBills = db.PurchaseBills.Where(
p => p.BillDate >= DateTime.Now.Date &&
p.BillDate < DateTime.Now.AddDays(1).Date &&
!(bool)p.IsDeleted).OrderBy(p => p.BillID);
if (purchaseBills.Count() >0)
{
var firstBill= purchaseBills.First(); //This is supported
//Attempt 1
var lastBill = purchaseBills.Last(); // Not supported
//Attempt 2
var lastBill = purchaseBills.LastOrDefault(); //Not supported
//Attempt 3
var lastBill = purchaseBills.Reverse().First(); //Not supported
textBoxPurchaseBillFrom.Text = firstBill.BillNo.ToString();
textBoxPurchaseBillTo.Text = lastBill.BillNo.ToString();
}
Update: --Errors--
Attempt 1: The query operator 'Last' is not supported.
Attempt 2: The query operator 'LastOrDefault' is not supported.
Attempt 3: The query operator 'Reverse' is not supported.
解决方案
- Instead of putting it into an own list by calling
ToList()
orToArray()
i would prefer to useAsEnumerable()
. - Additionally like the others you should try
OrderByDescending()
- Instead of
Count()
i would useAny()
.
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