error with select using Scope_Identity

Question

I am trying to understand what is wrong with this select. I want to get the last user_Id which was been added.

Here is the error message: The parameterized query '(@Id_user int)SELECT SCOPE_IDENTITY() AS id_user' expects the parameter '@Id_user', which was not supplied.

Here is the SQL statement:

        if (count >= 1)   /* <===  verification from the insert SQL  */
        {
            string selectStatement = "SELECT SCOPE_IDENTITY() AS id_user";
            SqlCommand selectCommand = new SqlCommand(selectStatement, sqlConnection);
            selectCommand.Parameters.Add("@Id_user", SqlDbType.Int, 0, "Id_user");
            int newID = (int)selectCommand.ExecuteScalar();

            int User_ID = Convert.ToInt32(selectCommand.Parameters["@Id_user"].Value);
            Session["Id_user"] = User_ID;

            buserIdAuthenticated = true;                   
            Session["userIdAuthenticated"] = buserIdAuthenticated;
            Response.Redirect("../pages/Welcome.aspx");
        }
    }

    catch (SqlException ex)
    {
        lblMessage.Text = ex.Message;
    }

    finally
    {
        sqlConnection.Close();
    }

Answer 1

you haven't defined an @parameter in your sql statement so you don;t need to add the parameter at all - just get the result of ExecuteScalar - you should be able to cast it to an int - although I cast it specifically in the sql statement too -

select cast(Scope_identity() as int) ....

so you'd end up with somthing like

        string selectStatement = "SELECT cast(SCOPE_IDENTITY() AS int)";
        SqlCommand selectCommand = new SqlCommand(selectStatement, sqlConnection);
        object newIDobj = (int)selectCommand.ExecuteScalar();
        if(newIDobj!=null)
            Session["Id_user"] = (int)newIDobj;

Even better you could create a stored procedure and have the insert done there, where it can then return scope identity.

Edited to include example with insert. (just typed in here - so likely some typos)

int newID = -1;
string commandString = "insert (code, desc, numbervalue) values (@code,    @desc,@numbervalue); select cast(scope_identity() as int);"
using(SqlCommand cmd = new SqlCommand(commandString))
{
    try
    {
          cmd.Parameters.Add("@code", )
          // etc
          int newid=(int)(cmd.ExecuteScalar()??-1);
    }
    catch(Exception e)
    {
         // something went wrong
    }
}

if(newID!=-1)
{
    // do something;
}