LINQ -如何根据DB返回的值修改select

Question

我对Linq比较陌生，我正在用。net开发一个函数，用Linq查询的选定字段实例化POCO。

问题是这些字段中的一个必须在"运行时"进行转换。

这是我的故障示例:

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

问题行是当我给属性AfbInfection赋值时。此属性的值与数据库中的PotentialInfection相反。所以如果I.PotentialInfection是True，那么我的属性AfbInfection应该是False。如上所述将导致IndexOutOfRangeException - Index在数组的边界之外不确定LinQ对not表达式做了什么，但肯定不是我想要的。

是否有任何方法来修改数据库字段值时存储到我的自定义对象?

谢谢!

Answer 1

试试这个:

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