LINQ-如何根據DB返回的值修改選擇

Question

我是Linq的新手，我正在使用.NET開發一個函數，該函數使用linq查詢的選定字段實例化POCO 。

問題在於這些字段之一必須在“運行時”進行轉換。

這是我的故障示例：

Private Shared Function GetInfectionHistory(HiveId As Long) As IList(Of HiveInfectionDetail)
    Using DB As LandDataModelUnitOfWork = Context.CreateUnitOfWork
            Dim historyResult = From I In DB.HiveAfbInfections
                                Where I.HiveId = HiveId
                                Select New HiveInfectionDetail With {
                                    .DateInfected = I.DateInfected,
                                    .DateCleaned = I.DateCleared,
                                    .PotentialAfbInfection = I.PotentialInfection,
                                    .AfbInfection = Not I.PotentialInfection
                                }
            If IsListEmpty(historyResult.ToList()) Then
                Return Nothing
            End If
            Return historyResult.ToList()
        End Using
End Function

和

Private Shared Function IsListEmpty(Of T)(source As IEnumerable(Of T)) As Boolean
        If source Is Nothing Then
            Return True
        End If
        Return Not source.Any()
    End Function
enter code here

問題行是當我為屬性AfbInfection分配值時。 此屬性將與數據庫中的PotentialInfection值相反。 因此，如果I.PotentialInfection為True，則我的屬性AfbInfection應該為False。 如上所述執行此操作將導致IndexOutOfRangeException-索引不在數組的范圍內，不確定LinQ使用該NOT表達式正在做什么，但是肯定不是我想要的。

將數據庫字段值存儲到我的自定義對象中時，有什么方法可以修改它？

謝謝！

Answer 1

嘗試這個：

Private Shared Function GetInfectionHistory(HiveId As Long) As IList(Of HiveInfectionDetail)
    Using DB As LandDataModelUnitOfWork = Context.CreateUnitOfWork
            Dim historyQuery1 = From I In DB.HiveAfbInfections
                                Where I.HiveId = HiveId
                                Select New With {
                                    .DateInfected = I.DateInfected,
                                    .DateCleaned = I.DateCleared,
                                    .PotentialInfection = I.PotentialInfection
                                }
            Dim historyQuery2 = From I In historyQuery1.ToArray()
                                Select New HiveInfectionDetail With {
                                    .DateInfected = I.DateInfected,
                                    .DateCleaned = I.DateCleaned,
                                    .PotentialAfbInfection = I.PotentialInfection,
                                    .AfbInfection = Not I.PotentialInfection
                                }
            Dim historyResult = historyQuery2.ToList()
            If IsListEmpty(historyResult) Then
                Return Nothing
            End If
            Return historyResult
        End Using
End Function