在循环中加载 sql 参数时出错，VB.Net

Question

我目前在 Microsoft visual studio express 2013 工作，后端为 sql。我正在尝试运行循环遍历 2 个组合框和一个 datetimepicker，用于选中复选框的任何实例。但是，我运行遇到了一个错误，它显示 "System.ArgumentException: No Mapping exists from Object type system.windows.forms.datetimepicker to a known managed provider native type." 当我运行代码时，我已经对参数值进行了观察，并且它没有将数据保存到变量之前sql 命令触发。我想我需要以不同的方式存储变量以允许访问变量。这是我的代码：

Try

Using conn1 As New SqlConnection(connstring)
    conn1.Open()
    Using comm1 As New SqlCommand("SELECT isnull(max(AuditID) + 1, 1) as 'AuditID' FROM table1", conn1)
        Dim reader1 As SqlDataReader = comm1.ExecuteReader
        reader1.Read()
        Dim AuditID As Integer = reader1("AuditID")
        reader1.Dispose()

        'Loop through all checkboxes and write into sql tables
        Dim Run As Integer
        For Run = 1 To 5
            Dim LineItem = DirectCast(Me.Controls("CB" & Run), CheckBox)
            If LineItem.Checked = True Then
                Dim DateTime = DirectCast(Me.Controls("DTP" & Run), DateTimePicker)
                Dim Frequency = DirectCast(Me.Controls("CBWeek" & Run), ComboBox)
                Dim Repeat = DirectCast(Me.Controls("CBRepeat" & Run), ComboBox)

                'sql statements
                'select ID
                Using conn2 As New SqlConnection(connstring)
                    conn2.Open()
                    Using comm2 As New SqlCommand("SELECT isnull(max(AuditID) + 1, 1) as 'ID' FROM table1", conn1)
                        Dim reader As SqlDataReader = comm2.ExecuteReader
                        reader.Read()
                        Dim ID As Integer = reader("ID")
                        reader.Dispose()

                        'Insert into table audit line
                        Using conn3 As New SqlConnection(connstring)
                            conn3.Open()
                            Using comm3 As New SqlCommand("INSERT INTO table1 (ID, AuditID, DateStart, Freq, repeats) " _
                                                          & "VALUES (@ID, @AuditID, @DateStart, @Freq, @Repeats)", conn3)
                                With comm3.Parameters
                                    .AddWithValue("@ID", ID)
                                    .AddWithValue("@AuditID", AuditID)
                                    .AddWithValue("@DateStart", DateTime)
                                    .AddWithValue("@Freq", Frequency)
                                    .AddWithValue("@Repeats", Repeat)
                                End With
                                comm3.ExecuteNonQuery()
                            End Using
                            conn3.Close()
                        End Using
                    End Using
                    conn2.Close()
                End Using
            End If
        Next
    End Using
    conn1.Close()
End Using

Catch ex As Exception
    MsgBox(ex.ToString)

我的 try 语句在这一行停止了我的代码：

 comm3.ExecuteNonQuery()

但是，我知道这个错误是在我添加参数时出现的，特别是这 3 行：

.AddWithValue("@DateStart", DateTime)
.AddWithValue("@Freq", Frequency)
.AddWithValue("@Repeats", Repeat)

我正在尝试根据此处的设计名称使用循环语句获取这些变量：

Dim DateTime = DirectCast(Me.Controls("DTP" & Run), DateTimePicker)
Dim Frequency = DirectCast(Me.Controls("CBWeek" & Run), ComboBox)
Dim Repeat = DirectCast(Me.Controls("CBRepeat" & Run), ComboBox)

程序似乎不喜欢使用上面的这些维度插入 sql table。有谁知道我可以将这些值传递给 sql 参数语句的方法吗？

Answer 1

我已经解决了这个问题，我需要将我的循环变量放入 .value 类型变量中。我添加了这个来修复它：

              Dim DateTime = DirectCast(Me.Controls("DTP" & Run), DateTimePicker)
                        Dim Frequency = DirectCast(Me.Controls("CBWeek" & Run), ComboBox)
                        Dim Repeat = DirectCast(Me.Controls("CBRepeat" & Run), ComboBox)



                        Dim Time As Date = DateTime.Value
                        Dim Freq As Integer = Frequency.SelectedValue
                        Dim Again As Integer = Repeat.SelectedValue

Answer 2

有很多事情我会做不同的事情。首先，始终使用 Option Strict，它会捕获您正在进行的一些类型转换。

我会从显式列表中获取控件，而不是从 Controls 中获取控件。只需制作几个数组来保存控件引用，这样您就不需要在集合中找到它们：

Private DTPs As DateTimePicker() = {DTP1, DTP2...}

这将避免转换它们的需要，减少箍和隐式转换，如 "DTP" & Run:

Dim dt As DateTime           ' vars for the SQL
Dim freq As Integer
For Run As Integer = 0 To 4
    dt = DTPs(Run).Value
    freq = cboFreq(Run).SelectedValue
    ...

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