Question

我在其他地方使用过这段代码，效果很好。那么为什么它会在第一个AddWithValue命令中给我一个空值异常？我假设其他人会遇到同样的问题。

这是标记：

Select a Category:<br />
<asp:DropDownList ID="ddlCategory" runat="server" AutoPostBack="True"
    DataSourceID="AccessDataSource1" DataTextField="ORG_NAME" 
    DataValueField="ID">
</asp:DropDownList>

<asp:AccessDataSource ID="AccessDataSource1" runat="server"
    DataFile="~/App_Data/webvideos.mdb"
    SelectCommand="SELECT * FROM [ORGANIZATIONS]"/>
<br />

Select an Organization:<br />
<asp:DropDownList ID="ddlOrg" runat="server"
    DataSourceID="AccessDataSource2" DataTextField="SectionName"
    DataValueField="ID">
</asp:DropDownList>

<asp:AccessDataSource ID="AccessDataSource2" runat="server"
    DataFile="~/App_Data/webvideos.mdb"
    SelectCommand="SELECT ID,SectionName FROM ORG_SECTIONS WHERE OrgID=@OrgID ">
    <SelectParameters>
        <asp:ControlParameter ControlID="ddlCategory"
            PropertyName="SelectedValue"
            Name="ID" Type="String"
            DefaultValue="" />
    </SelectParameters>
</asp:AccessDataSource>
<br />

Select an Attorney:<br />
<asp:DropDownList ID="ddlAtty" runat="server" 
    DataSourceID="AccessDataSource3" DataTextField="Expr1" DataValueField="ATTY_ID">
</asp:DropDownList>

<asp:AccessDataSource ID="AccessDataSource3" runat="server" 
    DataFile="~/App_Data/webvideos.mdb" 
    SelectCommand="SELECT ATTY_ID, NAME & ' ' & INITIAL & ' ' & LASTNAME AS Expr1 FROM ATTORNEYS ORDER BY NAME & INITIAL & ' ' & LASTNAME">
</asp:AccessDataSource>
<br />
<br />


<asp:Button ID="Button1" runat="server" Text="Submit" OnClick="AddRec" />

这是背后的代码：

protected void AddRec(object sender, EventArgs e)
{
    DropDownList ddlCategory = (DropDownList)this.FindControl("ddlCategory");
    DropDownList ddlOrg = (DropDownList)this.FindControl("ddlOrg");
    DropDownList ddlAtty = (DropDownList)this.FindControl("ddlAtty");

    string constr = @"Provider=Microsoft.Jet.OLEDB.4.0;Data Source=|DataDirectory|\webvideos.mdb;";
    string cmdstr = "INSERT INTO [Org_Sec_Atty] ([OrgID], [SecID], [AttyID]) VALUES (?, ?, ?)";


    OleDbConnection con = new OleDbConnection(constr);
    OleDbCommand com = new OleDbCommand(cmdstr, con);

    con.Open();
    com.Parameters.AddWithValue("@OrgID", ddlCategory.SelectedValue);
    com.Parameters.AddWithValue("@SecID", ddlOrg.SelectedValue);
    com.Parameters.AddWithValue("@AttyID", ddlAtty.SelectedValue);
    com.ExecuteNonQuery();
    con.Close();
    Response.Redirect("ManageProfAffs.aspx");
}

我的Org_Sec_Atty表（ID字段）中还有一个字段是自动递增的。我需要以某种方式记账吗？非常感谢任何帮助，谢谢你。

为什么我有空值？

0 个答案: