如何将一个可空的guid与一个linq查询中的guid进行比较？

Question

我得到一个错误，当这种尝试运行：

Nullable<Guid> ng = corpid; 

    var qry1 = from c in entities.Transactions 
      join p in entities.Products on c.CorporationId equals (Nullable<Guid>) p.CorporationId 
       where c.Branch == br && 
        c.AccountNumber == accountnumber && 
        c.CorporationId == ng 
       orderby c.TransactionDate descending 
       select new 
       { 
       Date = c.TransactionDate, 
       RefNo = c.ReferenceNumber, 
       DlvryAcct = c.DeliveryAccount, 
       Desc = p.Description, 
       GasQty = c.GasQuantity, 
       Total = c.Amount, 
       Balance = c.Balance 
       }; 

这是消息：

 
LINQ to Entities does not recognize the method 
'System.Linq.IQueryable`1[f__AnonymousType1`7[System.Nullable`1[System.DateTime], 
    System.String,System.String,System.String,System.Nullable`1[System.Decimal], 
    System.Nullable`1[System.Decimal],System.Nullable`1[System.Decimal]]] 
Reverse[f__AnonymousType1`7](System.Linq.IQueryable`1[f__AnonymousType1`7[System.Nullable`1[System.DateTime], 
    System.String,System.String,System.String,System.Nullable`1[System.Decimal], 
    System.Nullable`1[System.Decimal],System.Nullable`1[System.Decimal]]])' 
method, and this method cannot be translated into a store expression. 

我不认为中投可空GUID是在这里工作。 c.CorporationId是一个可以为空的指导，但p.corporationid只是一个指导。

有什么建议吗？

Answer 1

您是否尝试过前述的铸造和等同c.CorporationId到ng.Value代替？：

Nullable<Guid> ng = corpid; 

    var qry1 = from c in entities.Transactions 
      join p in entities.Products on c.CorporationId equals p.CorporationId 
       where c.Branch == br && 
        c.AccountNumber == accountnumber && 
        c.CorporationId == ng.Value 
       orderby c.TransactionDate descending 
       select new 
       { 
       Date = c.TransactionDate, 
       RefNo = c.ReferenceNumber, 
       DlvryAcct = c.DeliveryAccount, 
       Desc = p.Description, 
       GasQty = c.GasQuantity, 
       Total = c.Amount, 
       Balance = c.Balance 
       }; 

Answer 2

这似乎是在抱怨SELECT子句中的匿名构造函数。 c.TransactioDate,c.GasQuantity,c.Amount和c.Balance都显示为可空。尝试这样的事情，看看这些领域是否是问题。

Nullable<Guid> ng = corpid; 

var qry1 = from c in entities.Transactions 
      join p in entities.Products on c.CorporationId equals (Nullable<Guid>) p.CorporationId 
      where c.Branch == br && 
       c.AccountNumber == accountnumber && 
       c.CorporationId == ng.Value 
      orderby c.TransactionDate descending 
      select new 
      { 
       Date = c.TransactionDate.Value, 
       RefNo = c.ReferenceNumber, 
       DlvryAcct = c.DeliveryAccount, 
       Desc = p.Description, 
       GasQty = c.GasQuantity.Value, 
       Total = c.Amount.Value, 
       Balance = c.Balance.Value 
      }; 

Answer 3

这是一个古老的问题，但由于没有答案，所以这里就是骨感。在C＃中GUID是一个非空的对象，所以你永远不能映射为null的Guid，但你可以映射NULL来的Guid？所以这里的解决方案：

var qry1 = from c in entities.Transactions 
       join p in entities.Products on c.CorporationId equals p.CorporationId 
      where c.Branch == branch 
       && c.AccountNumber == accountNumber 
       && ((Guid?)c.CorporationId).Value == null // This is the secret sauce 
      orderby c.TransactionDate descending 
      select new 
        { 
         Date = c.TransactionDate, 
         RefNo = c.ReferenceNumber, 
         DlvryAcct = c.DeliveryAccount, 
         Desc = p.Description, 
         GasQty = c.GasQuantity, 
         Total = c.Amount, 
         Balance = c.Balance 
        }; 

不过，我可能会做这样的：

var qry1 = from c in entities.Transactions.Where(t => ((Guid?)t.CorporationId).Value == null) 
       join p in entities.Products on c.CorporationId equals p.CorporationId 
      where c.Branch == branch 
       && c.AccountNumber == accountNumber 
      orderby c.TransactionDate descending 
      select new 
        { 
         Date = c.TransactionDate, 
         RefNo = c.ReferenceNumber, 
         DlvryAcct = c.DeliveryAccount, 
         Desc = p.Description, 
         GasQty = c.GasQuantity, 
         Total = c.Amount, 
         Balance = c.Balance 
        }; 

但是你要问，如果你有，为什么模型此列确定施放此为不可为空的（如果设置正确，你可能不会面临不得不投的问题在此刻）。