c# - 如何在 linq 查询中将可为空的 guid 与 guid 进行比较？

Question

尝试运行时出现错误:

 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.

我认为强制转换为可空 guid 在这里不起作用。 c.CorporationId 是一个可为 null 的 guid，而 p.corporationid 只是一个 guid。

有什么建议吗？

Answer 1

您是否尝试过放弃转换并将 c.CorporationId 等同于 ng.Value？:

 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
              };