如何在Visual Studio中解决此错误："Parameter ?_1 has no default value."？

Question

我正在创建一个带有一些"代码隐藏"的 asp.net Web 表单，用于将数据发送到 MS Access 数据库。

提交表单后，我收到"参数 ？_1 没有默认值"。我已经浏览了大约 6 个网站，但我找不到足够接近我的解决方案，我可以在有限的 VB 词汇中使用。我对VB或C#语言不是很熟悉（我只用过Java和C++）。

我是否需要默认值，如果需要，如何添加默认值？

以下是.aspx.vb代码（错误源于何处）：

   Imports System.Data.OleDb
Partial Class _Default
    Inherits System.Web.UI.Page
    Protected Sub SciFairSubmit_Click(sender As Object, e As EventArgs) Handles SciFairSubmit.Click
        'form data requests----------------------------------------------------------------------------C:UsersNCG-PCWebmasteringTamugSciFair13WebSite1Default1.aspx.vb
        Dim strName As String = Request.Form("FirsNtame") 'In paraenthesis may be the item name in the form
        Dim strLasNtame As String = Request.Form("LasNtame")
        Dim strStudentEmail As String = Request.Form("StudentEmail")
        Dim strSchool As String = Request.Form("School")
        Dim numGrade As Integer = Request.Form("Grade") '*Dropdown list
        Dim strTeacher As String = Request.Form("Teacher") 'Teacher's LasNtame name
        Dim strTeacherEmail As String = Request.Form("TeacherEmail")
        Dim strCatagory As String = Request.Form("Catagory") '*Dropdown list
        Dim strExibitTite As String = Request.Form("ExibitTite") 'Note : "Title" by itself is a keyword and cannot be used
        Dim strElectricity As String = Request.Form("Electricity") '*possible boolean for electricity
        'Open Db Connection---------------------------------------------------------------------------------------------------------
        Dim strSQL As String
        Dim dbconn As OleDbConnection = Nothing
        dbconn = New OleDbConnection("Provider=Microsoft.ACE.OLEDB.12.0;data source=" & Server.MapPath("GalvestonScienceFairApp_Datasf13.mdb"))
        dbconn.Open()
        'SQL actions ----------------------------------------------------------------------------------------------------------
        strSQL = "INSERT INTO Exhibits (FirsNtame, LasNtame, StudentEmail, School, Grade, Teacher, TeacherEmail, Category, ExibitTite, Electricity) values (@FirsNtame, @LasNtame, @StudentEmail, @School, @Grade, @Teacher, @TeacherEmail, @Category, @ExibitTite, @Electricity)"
        Dim objcmd = New OleDbCommand(strSQL, dbconn)
        objcmd.Parameters.Add(New System.Data.OleDb.OleDbParameter("@FirsNtame", strName))
        objcmd.Parameters.Add(New System.Data.OleDb.OleDbParameter("@LasNtame", strLasNtame))
        objcmd.Parameters.Add(New System.Data.OleDb.OleDbParameter("@StudentEmail", strStudentEmail))
        objcmd.Parameters.Add(New System.Data.OleDb.OleDbParameter("@School", strSchool))
        objcmd.Parameters.Add(New System.Data.OleDb.OleDbParameter("@Grade", numGrade))
        objcmd.Parameters.Add(New System.Data.OleDb.OleDbParameter("@Teacher", strTeacher))
        objcmd.Parameters.Add(New System.Data.OleDb.OleDbParameter("@TeacherEmail", strTeacherEmail))
        objcmd.Parameters.Add(New System.Data.OleDb.OleDbParameter("@Category", strCatagory))
        objcmd.Parameters.Add(New System.Data.OleDb.OleDbParameter("@ExibitTite", strExibitTite))
        objcmd.Parameters.Add(New System.Data.OleDb.OleDbParameter("@Electricity", strElectricity))

        objcmd.ExecuteNonQuery()
        'Number of query values and destination fields are not the same.
        'Close DB Connection
        dbconn.Close()
        Response.Write("Thank you for registering!")
    End Sub
End Class

这是.asp页面（我很确定错误不是来自这里）：

<%@ Page Language="VB" MasterPageFile="~/Site.master" AutoEventWireup="false" CodeFile="ScienceFair.aspx.vb" Inherits="_Default" %>
<asp:Content ID="Content1" ContentPlaceHolderID="HeadContent" Runat="Server">

    <style type="text/css">
        .auto-style1 {
            text-align: center;
        }
    </style>

</asp:Content>
<asp:Content ID="Content2" ContentPlaceHolderID="MainContent" Runat="Server">
    <div id="RuleBreaker">
    <h2 class="auto-style1">Science Fair Registration</h2>
    <p class="auto-style1" >
        First Name:
        <br />
        <asp:TextBox ID="FirsNtame" runat="server" AutoCompleteType="FirstName"></asp:TextBox>
        <br />
<asp:RequiredFieldValidator id="FirsNtameValidator1" runat="server"
  ControlToValidate="FirsNtame"
  ErrorMessage="A first name is required."
  ForeColor="Red">
</asp:RequiredFieldValidator>
        <br />
        Last Name:
        <br />
        <asp:TextBox ID="LasNtame" runat="server" AutoCompleteType="LastName"></asp:TextBox>
        <br />
<asp:RequiredFieldValidator id="LasNtameValidator2" runat="server"
  ControlToValidate="LasNtame"
  ErrorMessage="A last name is required."
  ForeColor="Red">
</asp:RequiredFieldValidator>
        <br />
        Student Email Address:
        <br />
        <asp:TextBox ID="StudentEmail" runat="server" AutoCompleteType="Email"></asp:TextBox>
        <br />
<asp:RequiredFieldValidator id="StudentEmailValidator3" runat="server"
  ControlToValidate="StudentEmail"
  ErrorMessage="A Student Email is required."
  ForeColor="Red">
</asp:RequiredFieldValidator>
         <br />
         <br />
        School:
         <br />
        <asp:TextBox ID="School" runat="server"></asp:TextBox>
        <br />
<asp:RequiredFieldValidator id="SchoolValidator4" runat="server"
  ControlToValidate="School"
  ErrorMessage="Your school name is required."
  ForeColor="Red">
</asp:RequiredFieldValidator>
         <br />
        Grade:
        <br />
            <asp:DropDownList id="Grade" runat="server" Width="86px">
                <asp:ListItem>7</asp:ListItem>
                <asp:ListItem>8</asp:ListItem>
                <asp:ListItem>9</asp:ListItem>
                <asp:ListItem>10</asp:ListItem>
                <asp:ListItem>11</asp:ListItem>
                <asp:ListItem>12</asp:ListItem>
            </asp:DropDownList>
        <br />
<asp:RequiredFieldValidator id="GradeValidator5" runat="server"
  ControlToValidate="Grade"
  ErrorMessage="A grade is required."
  ForeColor="Red">
</asp:RequiredFieldValidator>
        <br />
            Teacher's Last Name (only):<br />
            <asp:TextBox id="Teacher" runat="server" Width="500px"></asp:TextBox>
            <br />
<asp:RequiredFieldValidator id="TeacherValidator6" runat="server"
  ControlToValidate="Teacher"
  ErrorMessage="A teacher last name is required."
  ForeColor="Red">
</asp:RequiredFieldValidator>
        <br />
            Teacher E-mail:<br />&nbsp;<asp:TextBox ID="TeacherEmail" runat="server" 
                Width="500px"></asp:TextBox>
            <br /> 
<asp:RequiredFieldValidator id="TeacherEmailValidator7" runat="server"
  ControlToValidate="TeacherEmail"
  ErrorMessage="A teacher email is required field."
  ForeColor="Red">
</asp:RequiredFieldValidator>
        <br />
            <%-- Teacher Phone Number:<br />&nbsp;<asp:TextBox id="TPhone" runat="server" Width="500px"></asp:TextBox> --%>
            <%-- Might put the above in later --%>
            Catagory :<br />&nbsp;<asp:DropDownList id="Catagory" runat="server" Width="212px">
                <asp:ListItem>Behavorial &amp; Social Sciences</asp:ListItem>
                <asp:ListItem>Biochemistry &amp; Microbiology</asp:ListItem>
                <asp:ListItem>Botany</asp:ListItem>
                <asp:ListItem>Environmental Sciences</asp:ListItem>
                <asp:ListItem>Medicine &amp; Health</asp:ListItem>
                <asp:ListItem>Zoology</asp:ListItem>
                <asp:ListItem>Chemistry</asp:ListItem>
                <asp:ListItem>Computer Science</asp:ListItem>
                <asp:ListItem>Earth &amp; Space Sciences</asp:ListItem>
                <asp:ListItem>Engineering</asp:ListItem>
                <asp:ListItem>Mathematics</asp:ListItem>
                <asp:ListItem>Physics</asp:ListItem>
            </asp:DropDownList>
            <br />
<asp:RequiredFieldValidator id="CatagoryValidator8" runat="server"
  ControlToValidate="Catagory"
  ErrorMessage="A catagory is required."
  ForeColor="Red">
</asp:RequiredFieldValidator>
        <br />
            Exibit Title :<br />&nbsp;<asp:TextBox id="ExibitTite" runat="server" Width="500px"></asp:TextBox>
            <br />
<asp:RequiredFieldValidator id="ExibitTiteValidator9" runat="server"
  ControlToValidate="ExibitTite"
  ErrorMessage="A title is required."
  ForeColor="Red">
</asp:RequiredFieldValidator>
        <br />
            Does your exhibit use electricity?<br />
            <%-- Possible issues here, may need to use 1 & 0 instead--%>
            <asp:DropDownList id="Electricity" runat="server">
                <asp:ListItem Value="Yes">Yes</asp:ListItem>
                <asp:ListItem Value="No">No</asp:ListItem>
            </asp:DropDownList>
        <br />
 <asp:RequiredFieldValidator id="ElectricityValidator10" runat="server"
  ControlToValidate="Electricity"
  ErrorMessage="Does your computer use electricity?"
  ForeColor="Red">
</asp:RequiredFieldValidator>
        <br />
    </p>
        <p class="auto-style1" >
            <asp:Button ID="SciFairSubmit" runat="server" Text="Submit" />
            <br />
            <br />
    </p>
    </div>
</asp:Content>

Answer 1

查询应为：

INSERT INTO Exhibits (FirsNtame, LasNtame, StudentEmail, School, Grade, Teacher, TeacherEmail, Category, ExibitTite, Electricity) values (@FirsNtame, @LasNtame, @StudentEmail, @School, @Grade, @Teacher, @TeacherEmail, @Category, @ExibitTite, @Electricity)

请参阅：使用参数访问 2007 oledb 示例。问号用于旧的 ADO 而不是 ADO.NET

编辑参数值不能为空。设置为无的参数将被视为缺失。

可能的提示：

Dim strLasNtame As String = if(Request.Form("LasNtame"),"")
objcmd.Parameters.Add(New System.Data.OleDb.OleDbParameter("@FirsNtame", if(strName,DBNull.Value)))
For Each param As System.Data.OleDb.OleDbParameter In objcmd.Parameters
  If param.Value Is Nothing Then
     param.Value = DBNull.Value
  End If
Next

Answer 2

在尝试传递可能为"null"的字符串参数时，我遇到了这个问题，使用一些 C# 代码，解决方案很简单：

  cmd.Parameters.AddWithValue("@TEXTCOL", myString ?? (object)DBNull.Value);