不支持 Last 和 LastOrDefault

问题描述

我正在尝试获取列表中的第一个和最后一个值.支持查询运算符 First()，但 Last() 和 LastOrDefault() 会出错.我是否错误地使用了 Last() 运算符?

I am trying to get the first and last values in a list. The query operator First() is supported but Last() and LastOrDefault() give an error. Am I using the Last() operator incorrectly?

var purchaseBills = db.PurchaseBills.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();
}

更新:

--错误--

尝试 1:不支持查询运算符Last".

Attempt 1: The query operator 'Last' is not supported.

尝试 2:不支持查询运算符LastOrDefault".

Attempt 2: The query operator 'LastOrDefault' is not supported.

尝试 3:不支持查询运算符Reverse".

Attempt 3: The query operator 'Reverse' is not supported.

问题描述

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