vb.net - 如何通过反射对对象的可为空属性调用 HasValue？

Question

此函数循环对象的所有属性以创建更新查询以将对象保存到数据库。

由于引入了可为 null 的属性，我们必须对其进行一些更改。如果该属性可为空，我们想检查“HasValue”属性。当它具有值(value)时，这确实有效。当该属性没有值时，我们会在 CBool​​ 行收到“非静态方法需要目标”错误

有什么建议吗？使用反射检查属性的“HasValue”属性的另一种方法？

谢谢。

Private Function GetUpdateQuery(ByVal obj As Object, ByRef params As List(Of SqlParameter), Optional ByVal excl As String() = Nothing) As String
     Dim sql As String = String.Empty

     Dim props As PropertyInfo() = obj.GetType().GetProperties

     If excl Is Nothing Then
          excl = New String() {}
     End If

     For Each prop As PropertyInfo In props
          Try
               If Not excl.Contains(prop.Name) And prop.CanWrite = True Then
                    sql &= String.Format("{0} = @{1},", prop.Name, prop.Name)

                    Dim param As SqlParameter

                    Dim value As Object

                    If prop.PropertyType.IsGenericType AndAlso prop.PropertyType.GetGenericTypeDefinition() = GetType(Nullable(Of )) Then

                         If CBool(prop.PropertyType.GetProperty("HasValue").GetValue(prop.GetValue(obj, Nothing), Nothing)) Then
                              value = prop.GetValue(obj, Nothing)
                         Else
                              value = DBNull.Value
                         End If
                    Else
                         If prop.GetValue(obj, Nothing) = Nothing Then
                              value = DBNull.Value
                         Else
                              value = prop.GetValue(obj, Nothing)
                         End If
                    End If
                    param = ConnSql.CreateParameter("@" & prop.Name, value)

                    params.Add(param)
               End If
          Catch ex As Exception

          End Try

     Next

     sql = sql.Substring(0, sql.Length - 1)

     Return sql
End Function

Answer 1

您不需要以下If。您可以将其删除。

If prop.PropertyType.IsGenericType AndAlso prop.PropertyType.GetGenericTypeDefinition() = GetType(Nullable(Of )) Then

但是您确实需要修复以下If:

If prop.GetValue(obj, Nothing) = Nothing Then

至

If prop.GetValue(obj, Nothing) IS Nothing Then

--

完整代码:

Private Function GetUpdateQuery(ByVal obj As Object, ByRef params As List(Of SqlParameter), Optional ByVal excl As String() = Nothing) As String
     Dim sql As String = String.Empty

     Dim props As PropertyInfo() = obj.GetType().GetProperties

     If excl Is Nothing Then
          excl = New String() {}
     End If

     For Each prop As PropertyInfo In props
          If Not excl.Contains(prop.Name) And prop.CanWrite = True Then
               sql &= String.Format("{0} = @{1},", prop.Name, prop.Name)

               Dim param As SqlParameter

               Dim value As Object

               If prop.GetValue(obj, Nothing) Is Nothing Then
                    value = DBNull.Value
               Else
                    value = prop.GetValue(obj, Nothing)
               End If

               param = ConnSql.CreateParameter("@" & prop.Name, value)

               params.Add(param)
          End If
     Next

     sql = sql.Substring(0, sql.Length - 1)

     Return sql
End Function