参数@Something 没有默认值（访问数据库，Visual Studio VB.NET）

Question

我正在使用 Access 数据库来存储错误发生的记录，以跟踪错误的数量和频率。多亏了这个网站上一些有天赋的程序员的大力帮助，我现在离我的最终目标越来越近了，即将出现次数从数据库中提取出来，并放入 Visual Studio 程序的图表中。

我运行遇到的问题是我的函数中的这一行抛出错误：

count = command.ExecuteScalar()

错误如下：

System.Data.OleDb.OleDbException: 'Parameter @MY_OF_LOG has no default value.'

我成功地为计数返回了一个值，即 0。这是一个可能的值，但我现在想知道计数 returns 为零这一事实是否可能部分促成了这一点错误？

注意：每个月从这些计数返回的值将用作图表的 y 值。

有人知道为什么会出现这个错误吗？我将在下面插入我的代码片段。感谢您的帮助。

Private Function CountMissedParts() Handles MyBase.Load

    Dim sql = $"SELECT COUNT(*)
        FROM DataCollection
        WHERE [MISSED PART] = 'Missed Part'
        AND [M/Y OF LOG] = @MY_OF_LOG;"
    Dim JANmyOfLog = #1/1/2021#
    Dim FEBmyOfLog = #2/1/2021#
    Dim MARmyOfLog = #3/1/2021#
    Dim APRmyOfLog = #4/1/2021#
    Dim MAYmyOfLog = #5/1/2021#
    Dim JUNmyOfLog = #6/1/2021#
    Dim JULmyOfLog = #7/1/2021#
    Dim AUGmyOfLog = #8/1/2021#
    Dim SEPmyOfLog = #9/1/2021#
    Dim OCTmyOfLog = #10/1/2021#
    Dim NOVmyOfLog = #11/1/2021#
    Dim DECmyOfLog = #12/1/2021#
    Dim count As Integer
    Dim JanuaryMP As Double
    Dim FebruaryMP As Double
    Dim MarchMP As Double
    Dim AprilMP As Double
    Dim MayMP As Double
    Dim JuneMP As Double
    Dim JulyMP As Double
    Dim AugustMP As Double
    Dim SeptemberMP As Double
    Dim OctoberMP As Double
    Dim NovemberMP As Double
    Dim DecemberMP As Double

    Using connection As New OleDbConnection("Provider=Microsoft.ACE.OLEDB.12.0;Data Source=|DataDirectory|\Database1.accdb"),
            command As New OleDbCommand(sql, connection)
        JanuaryMP = command.Parameters.Add("@MY_OF_LOG", OleDbType.Date).Value = JANmyOfLog
        FebruaryMP = command.Parameters.Add("@MY_OF_LOG", OleDbType.Date).Value = FEBmyOfLog
        MarchMP = command.Parameters.Add("@MY_OF_LOG", OleDbType.Date).Value = MARmyOfLog
        AprilMP = command.Parameters.Add("@MY_OF_LOG", OleDbType.Date).Value = APRmyOfLog
        MayMP = command.Parameters.Add("@MY_OF_LOG", OleDbType.Date).Value = MAYmyOfLog
        JuneMP = command.Parameters.Add("@MY_OF_LOG", OleDbType.Date).Value = JUNmyOfLog
        JulyMP = command.Parameters.Add("@MY_OF_LOG", OleDbType.Date).Value = JULmyOfLog
        AugustMP = command.Parameters.Add("@MY_OF_LOG", OleDbType.Date).Value = AUGmyOfLog
        SeptemberMP = command.Parameters.Add("@MY_OF_LOG", OleDbType.Date).Value = SEPmyOfLog
        OctoberMP = command.Parameters.Add("@MY_OF_LOG", OleDbType.Date).Value = OCTmyOfLog
        NovemberMP = command.Parameters.Add("@MY_OF_LOG", OleDbType.Date).Value = NOVmyOfLog
        DecemberMP = command.Parameters.Add("@MY_OF_LOG", OleDbType.Date).Value = DECmyOfLog
        connection.Open()
        count = command.ExecuteScalar()

        ' set 0,0
        NotInEpicorCHRT.Series("Missed Part").Points.AddXY(0, 0)
        ' other points
        NotInEpicorCHRT.Series("Missed Part").Points.AddXY(1, JanuaryMP)

        NotInEpicorCHRT.Series("Missed Part").Points.AddXY(2, FebruaryMP)

        NotInEpicorCHRT.Series("Missed Part").Points.AddXY(3, MarchMP)

        NotInEpicorCHRT.Series("Missed Part").Points.AddXY(4, AprilMP)

        NotInEpicorCHRT.Series("Missed Part").Points.AddXY(5, MayMP)

        NotInEpicorCHRT.Series("Missed Part").Points.AddXY(6, JuneMP)

        NotInEpicorCHRT.Series("Missed Part").Points.AddXY(7, JulyMP)

        NotInEpicorCHRT.Series("Missed Part").Points.AddXY(8, AugustMP)

        NotInEpicorCHRT.Series("Missed Part").Points.AddXY(9, SeptemberMP)

        NotInEpicorCHRT.Series("Missed Part").Points.AddXY(10, OctoberMP)

        NotInEpicorCHRT.Series("Missed Part").Points.AddXY(11, NovemberMP)

        NotInEpicorCHRT.Series("Missed Part").Points.AddXY(12, DecemberMP)

    End Using
    NotInEpicorCHRT.ChartAreas(0).AxisX.Minimum = 0.0
    NotInEpicorCHRT.ChartAreas(0).AxisX.Maximum = 12
    NotInEpicorCHRT.ChartAreas(0).AxisX.Interval = 1
    NotInEpicorCHRT.ChartAreas(0).AxisY.Minimum = 0.0
    NotInEpicorCHRT.ChartAreas(0).AxisY.Maximum = 45
    NotInEpicorCHRT.ChartAreas(0).AxisY.Interval = 5

End Function

Answer 1

一个小警告：我对图表没有太多经验，但其他东西应该没问题。

重要的部分是：

Dim logDates() As DateTime ...

这声明了一个 DateTime 数组。当您打算遍历值时，数组是一种存储相同类型的多个值的简单方法。我还冒昧地使用 VB.Net DateTime 类型来明确说明年、月和日期值。这种方法将使您和阅读您代码的其他人更加清楚。

For counter As Integer = 0 To logDates.Count - 1

数据库命令执行 12 次，对数组中的每个条目执行一次。

   Using Command As New OleDbCommand(sql, connection)
       Command.Parameters.Add("MY_OF_LOG", OleDbType.Date).Value = logDates(counter)
       Dim returnValue = Command.ExecuteScalar()

       Dim count As Integer = Integer.Parse(returnValue.ToString)

       ' other points
       NotInEpicorCHRT.Series("Missed Part").Points.AddXY(counter + 1, count)
   End Using

ExecuteScalar 的 return 值然后使用您原来的索引放入图表系列

整个代码建议如下：

    Public Sub CountMissedParts()
        Dim logDates() As DateTime = {New DateTime(2021, 1, 1),
                                      New DateTime(2021, 2, 1),
                                      New DateTime(2021, 3, 1),
                                      New DateTime(2021, 4, 1),
                                      New DateTime(2021, 5, 1),
                                      New DateTime(2021, 6, 1),
                                      New DateTime(2021, 7, 1),
                                      New DateTime(2021, 8, 1),
                                      New DateTime(2021, 9, 1),
                                      New DateTime(2021, 10, 1),
                                      New DateTime(2021, 11, 1),
                                      New DateTime(2021, 12, 1)}

        ' set 0,0
        NotInEpicorCHRT.Series("Missed Part").Points.AddXY(0, 0)

        Using connection As New OleDbConnection("Provider=Microsoft.ACE.OLEDB.12.0;Data Source=|DataDirectory|\Database1.accdb")
            connection.Open()

            For counter As Integer = 0 To logDates.Count - 1
                Dim sql = $"SELECT COUNT(*) FROM DataCollection WHERE [MISSED PART] = 'Missed Part' AND [M/Y OF LOG] = @MY_OF_LOG;"
                Using Command As New OleDbCommand(sql, connection)
                    Command.Parameters.Add("MY_OF_LOG", OleDbType.Date).Value = logDates(counter)
                    Dim returnValue = Command.ExecuteScalar()

                    Dim count As Integer = Integer.Parse(returnValue.ToString)

                    ' other points
                    NotInEpicorCHRT.Series("Missed Part").Points.AddXY(counter + 1, count)
                End Using
            Next
        End Using

        NotInEpicorCHRT.ChartAreas(0).AxisX.Minimum = 0.0
        NotInEpicorCHRT.ChartAreas(0).AxisX.Maximum = 12
        NotInEpicorCHRT.ChartAreas(0).AxisX.Interval = 1
        NotInEpicorCHRT.ChartAreas(0).AxisY.Minimum = 0.0
        NotInEpicorCHRT.ChartAreas(0).AxisY.Maximum = 45
        NotInEpicorCHRT.ChartAreas(0).AxisY.Interval = 5
    End Sub

Answer 2

既然你已经接受了答案，我认为你的问题已经解决了。我的函数看起来像这样。

Private Function CountMissedParts() As DataTable
    Dim sql = "SELECT [M/Y OF LOG], COUNT([Missed Part]) As Total 
                FROM [Data Collection] 
                WHERE [MISSED PART] = 'MISSED PART' GROUP BY [M/Y OF LOG]  
                ORDER BY [M/Y OF LOG];"
    Using dt As New DataTable
        Using connection As New OleDbConnection("Provider=Microsoft.ACE.OLEDB.12.0;Data Source=|DataDirectory|\Database1.accdb"),
        command As New OleDbCommand(sql, connection)
            connection.Open()
            Using reader = command.ExecuteReader
                dt.Load(reader)
            End Using
        End Using
        Return dt
    End Using
End Function

用法。

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
    Dim dt = CountMissedParts()
    'Add a grid to your form just to see what data was returned
    'If all is well delete grid and the following line
    DataGridView1.DataSource = dt
    'To show you how to access the data
    'Inside the For loop is where you would put the code to fill you graph
    For Each row As DataRow In dt.Rows
        Debug.Print($"{row("M/Y OF LOG")}  -  {row("Total")}")
    Next
End Sub

顺便说一句，如果之前的答案没有成功，您可以再次点击检查并选择另一个答案。

参数@Something 没有默认值（访问数据库，Visual Studio VB.NET）

Parameter @Something Has No Default Value (Access Database, Visual Studio VB.NET)

vb.net

oledb

parameters

ms-access

visual-studio