Question

我有一个函数，它根据传入的变量值创建不同类型的表达式。

Protected Function BuildSortPredicate(ByVal tableType As Object, ByRef expr As Expression)
    Dim sortExpression As Expression
    If tableType Is "Job" Then
        sortExpression = Expression.Lambda(Of Func(Of Job, String))(expr)
    ElseIf tableType Is "User" Then
        sortExpression = Expression.Lambda(Of Func(Of User, Integer))(expr)
    ...
    End If
    Return sortExpression
End Function

如何避免冗长的if / else（或case switch）结构？理想情况下，我正在寻找这样的东西：

Protected Function BuildSortPredicate(ByVal tableType As Object, ByRef exprt As Expression)
    Dim sortExpression As Expression
    sortExpression = Expression.Lambda(Of Func(Of tableType, String))(expr)
    Return sortExpression
End Function

这里的总体目标是将表达式转换为适当的类型，以便我可以在LINQ查询中使用它。

Answer 1

您想要制作通用功能

Protected Function BuildSortPredicate(Of T)(ByVal expr As Expression) As Expression
    Dim sortExpression As Expression
    sortExpression = Expression.Lambda(Of Func(Of T, String))(expr)
    Return sortExpression
End Function

在表达式中使用属性类型

1 个答案: