C# LINQ select 来自列表，其中值不包含在数据库中

Question

我正在开发 .NET CORE 5 应用程序以及 Entity Framework CORE。我有字符串列表，我需要从列表中过滤掉数据库中不存在的记录，以便我只能处理这些记录。在接下来的尝试中，我得到了空错误。我正在使用 Contain 但不确定它是否真的适合，例如我有大约 4000 条记录

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();

Answer 1

当您的 PaymentSourceReference 为空时。您不能将 null 传递给 Contains 如果为空，则可以分配空字符串例如。 PaymentSourceReference??String.Empty

下面我已经修改了你的代码你可以检查里面包含的方法


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();

Answer 2

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

Answer 3

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();

C# LINQ select 来自列表，其中值不包含在数据库中

C# LINQ select from List where value is not contained in database

c#

linq

entity-framework-core

.net-5