C#LINQ從串列中選擇，其中值不包含在資料庫中-有解無憂

我正在開發 .NET CORE 5 應用程式和 Entity Framework CORE。我有字串串列，我需要從串列中過濾掉資料庫中不存在的記錄，以便我只能處理這些記錄。在以下嘗試中，我收到空錯誤。我正在使用 Contain 但不確定它是否真的適合，例如我有大約 4000 條記錄

error

   Value cannot be null. (Parameter 'value')

Code

 List<string> PaymentSourceReferences = new List<string>();
        PaymentSourceReferences.Add("e3gdf210-f933-ec11-xxxx-00505691aaaa");
        PaymentSourceReferences.Add("gg34b580-f843-ec11-xxxx-00505691rrrr");
        PaymentSourceReferences.Add("43gf353d-f8fe-ec11-xxxx-00505691tttr");
        PaymentSourceReferences.Add("h4gd5170-7943-ec11-xxxx-00505687bbbb");
        PaymentSourceReferences.Add("4gdv5170-7965-ec11-xxxx-005056874gdg");

   var d2 = (from x in PaymentSourceReferences
             where !x.Contains(db.myTable)
             select PaymentSourceReference).ToList();

uj5u.com熱心網友回復：

var d2 = PaymentSourceReferences.Where(x => !db.myTable.Any(t => t.Id == x)).ToList();

uj5u.com熱心網友回復：

這些當您PaymentSourceReference為空時。您不能將 null 傳遞給Contains 您可以分配空字串，如果它為 null，例如。PaymentSourceReference??String.Empty

下面我修改了你的代碼，你可以在 contains 方法中檢查


List<string> PaymentSourceReferences = new List<string>();
        PaymentSourceReferences.Add("e3gdf210-f933-ec11-xxxx-00505691aaaa");
        PaymentSourceReferences.Add("gg34b580-f843-ec11-xxxx-00505691rrrr");
        PaymentSourceReferences.Add("43gf353d-f8fe-ec11-xxxx-00505691tttr");
        PaymentSourceReferences.Add("h4gd5170-7943-ec11-xxxx-00505687bbbb");
        PaymentSourceReferences.Add("4gdv5170-7965-ec11-xxxx-005056874gdg");

  string PaymentSourceReference = null;
   var d2 = (from x in PaymentSourceReferences
             where !x.Contains(PaymentSourceReference??String.Empty)
             select PaymentSourceReference).ToList();

uj5u.com熱心網友回復：

找到答案；

  var existingPaymentReferences = 
           (from payment in db.BoPcnPayments
            where PaymentSourceReferences.Contains(payment.PaymentSourceReference)
            select payment.PaymentSourceReference).ToList();

  var paymentReferencesToProcess = 
           (from csvPayements in PaymentSourceReferences
            where !existingPaymentReferences.Contains(csvPayements)
            select csvPayements).ToList();

轉載請註明出處，本文鏈接：https://www.uj5u.com/gongcheng/318201.html

標籤：C＃林克实体框架核心 .net-5

上一篇：如何分組多列并計數？

下一篇：如何構造特定的linq查詢？