如何从DataTable提取指定列填充构造函数生成实体对象列表

现有代码核心问题 #

• 声明的lst1、lst2未初始化，直接调用Add方法会触发空引用异常
• 列名常量Summencode拼写与DataTable实际列名SummenCode（大写C）不匹配，会导致找不到列
• DataTable提供的列中不存在Gesamtmenge字段，需要你确认字段映射逻辑，以下示例暂时用Anzahl列转换为Integer作为替代，你可以根据实际业务调整
• 未处理DBNull值，直接转换类型会抛出异常
• 空Catch块吞掉所有异常，无法排查错误
• 没有判断传入的List参数是否为空，稳定性不足

修正后完整代码 #

Imports System.IO

Public Class MainForm

    ' 修正列名与DataTable实际值匹配
    Private Const KostenArt As String = "KostenArt"
    Private Const UANR As String = "UANR"
    Private Const Ueberbegriff As String = "Ueberbegriff"
    Private Const Benennung As String = "Benennung"
    Private Const Anzahl As String = "Anzahl"
    Private Const Einheit As String = "Einheit"
    Private Const Einzelkosten As String = "Einzelkosten"
    Private Const SummenCode As String = "SummenCode" ' 修正大小写匹配DataTable列名

    Public dt1, dt2 As DataTable
    Public lst1, lst2 As List(Of ISAACService)

    ' 窗体加载时初始化列表
    Private Sub MainForm_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        lst1 = New List(Of ISAACService)()
        lst2 = New List(Of ISAACService)()
    End Sub

    Private Sub btnDatei1_Click(sender As Object, e As EventArgs) Handles btnDatei1.Click
        If OpenFileDialog1.ShowDialog() = DialogResult.OK Then
            If File.Exists(OpenFileDialog1.FileName) Then
                dt1 = FileGenerator.ReadFromProtectedFile(OpenFileDialog1.FileName)
                dgv1.DataSource = dt1
                ' 转换前清空原有数据避免重复添加
                lst1.Clear()
                lst1 = ConvertDataTableToListOfISAACService(dt1, lst1)
            End If
        End If
    End Sub

    Private Sub btnDatei2_Click(sender As Object, e As EventArgs) Handles btnDatei2.Click
        If OpenFileDialog1.ShowDialog() = DialogResult.OK Then
            dt2 = FileGenerator.ReadFromProtectedFile(OpenFileDialog1.FileName)
            dgv2.DataSource = dt2
            lst2.Clear()
            lst2 = ConvertDataTableToListOfISAACService(dt2, lst2)
        End If
    End Sub

    Private Sub btnVergleich_Click(sender As Object, e As EventArgs) Handles btnVergleich.Click
        ' 后续对比逻辑可以直接使用lst1和lst2
        CompareDataTables(lst1, lst2)
    End Sub

    Private Sub CompareDataTables(ByVal lst1 As List(Of ISAACService), ByVal lst2 As List(Of ISAACService))
        ' 你的对比逻辑实现
    End Sub

    Private Function ConvertDataTableToListOfISAACService(dt As DataTable, lst As List(Of ISAACService)) As List(Of ISAACService)
        ' 自动初始化传入的空列表
        If lst Is Nothing Then lst = New List(Of ISAACService)()
        If dt Is Nothing OrElse dt.Rows.Count = 0 Then Return lst

        Try
            For Each row As DataRow In dt.Rows
                ' 处理DBNull值，设置默认值
                Dim kostenArtVal As String = If(row.IsNull(KostenArt), String.Empty, row(KostenArt).ToString())
                Dim uanrVal As String = If(row.IsNull(UANR), String.Empty, row(UANR).ToString())
                Dim ueberbegriffVal As String = If(row.IsNull(Ueberbegriff), String.Empty, row(Ueberbegriff).ToString())
                Dim benennungVal As String = If(row.IsNull(Benennung), String.Empty, row(Benennung).ToString())
                Dim anzahlVal As Double = If(row.IsNull(Anzahl), 0.0, CDbl(row(Anzahl)))
                Dim einheitVal As String = If(row.IsNull(Einheit), String.Empty, row(Einheit).ToString())
                Dim einzelkostenVal As Double = If(row.IsNull(Einzelkosten), 0.0, CDbl(row(Einzelkosten)))
                ' 注意：DataTable无Gesamtmenge列，此处暂时用Anzahl转Integer替代，你可根据实际业务修改映射逻辑
                Dim gesamtmengeVal As Integer = If(row.IsNull(Anzahl), 0, CInt(row(Anzahl)))
                Dim summenCodeVal As String = If(row.IsNull(SummenCode), String.Empty, row(SummenCode).ToString())

                Dim isaac As New ISAACService(kostenArtVal, uanrVal, ueberbegriffVal, benennungVal, anzahlVal, einheitVal, einzelkostenVal, gesamtmengeVal, summenCodeVal)
                lst.Add(isaac)
            Next
        Catch ex As Exception
            ' 输出错误提示方便排查
            MessageBox.Show($"转换数据出错：{ex.Message}", "错误", MessageBoxButtons.OK, MessageBoxIcon.Error)
        End Try

        Return lst
    End Function

End Class

注意事项 #

如果Gesamtmenge字段有其他映射逻辑，你只需要修改gesamtmengeVal的赋值代码即可，比如如果对应DataTable的Summenkosten列就把字段名换成"Summenkosten"。

内容的提问来源于stack exchange，提问作者idontgetit