C# 下拉列表选择的值未设置为 SQL select 语句存储过程

Question

I have a data-bound drop-down list of collegeID values and I want to select one of these values based on a collegeID in an SQL database. I have a stored procedure to select the ID, but the value is not being selected when the page is run.

My SQL stored procedure is as follows:

USE [CONNECTION]
GO
/****** Object:  StoredProcedure [db_owner].[CollegePersonSelectAll]    Script Date: 5/9/2022 10:50:18 PM ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
-- =============================================
-- Author:      Alexander Johnson
-- Create date: 5/9/2022
-- Description: CollegePersonSelectAll
-- =============================================
ALTER PROCEDURE [db_owner].[CollegePersonSelectAll]
    -- Add the parameters for the stored procedure here
    @personID int,
    @collegeID int
AS
BEGIN
    -- SET NOCOUNT ON added to prevent extra result sets from
    -- interfering with SELECT statements.
    SET NOCOUNT ON;

    -- Insert statements for procedure here
SELECT        collegeID
FROM            CollegePerson
WHERE           personID = @personID
END

The code in C# is as follows:

    protected void Page_Load(object sender, EventArgs e)
    {
        personID = RetrieveID();
        if (!Page.IsPostBack)
        {
            string dbConn = System.Configuration.ConfigurationManager.ConnectionStrings["CONNECTIONSTRING"].ConnectionString;
            SqlConnection conn = new SqlConnection(dbConn);
            using (SqlCommand cmd = new SqlCommand("[CollegePersonSelectAll]", conn))
            {
                cmd.CommandType = CommandType.StoredProcedure;
                cmd.Parameters.AddWithValue("@personID", personID);
                try
                {
                    conn.Open();
                    _updateCollege.SelectedValue = Convert.ToString(cmd.ExecuteScalar());
                    collegeID = Convert.ToString(cmd.ExecuteScalar());
                }
                catch (SqlException ex)
                {
                    this._message.Text = "Error from SQL " + ex.Message;
                }
            }
        }
    }

The HTML for the dropdown list is as follows:

        <asp:DropDownList ID="_college" runat="server" DataSourceID="sqlDataCollege" DataTextField="collegeName" DataValueField="collegeID" Width="157px" AppendDataBoundItems="True">
            <asp:ListItem Value="0" SelectedValue='%#bind("stateAbbrev")%>'>-Please Select-</asp:ListItem>
        </asp:DropDownList>

The _updateCollege.SelectedValue does not show the value from the database. Does anyone know why this is?

Answer 1

Remove @collegeID from the input parameter and use ExecuteScalar instead of ExecuteNonQuery .