Getting error as Invalid column name C#.NET

Question

I am new to C#.net. I am developing a small application where the data in one drop down list gets populated based on the value selected in another drop down list. Upon viewing the output, I am getting the error Invalid column name 'CategoryBasedList' . Can you please point out where I went wrong. I am attaching the code below. Thanks in advance.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data.SqlClient;
using System.Configuration;
using System.Data;


public partial class UserLogin : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
       if (!IsPostBack)
        {
          populate();
        }
    }
    protected void ddlCategoryBasedList_SelectedIndexChanged(object sender, EventArgs e)
        {

        }

    protected void ddlListOfBooks_SelectedIndexChanged(object sender, EventArgs e)
        {

        string constr = ConfigurationManager.ConnectionStrings["CONN_STR"].ToString();
        SqlConnection con = new SqlConnection(constr);
        con.Open();
        SqlCommand com = new SqlCommand("Select distinct(CategoryBasedList) from Category where CategoryList = '" +  (ddlListOfBooks.SelectedValue).ToString() + "'", con);
        SqlDataAdapter da = new SqlDataAdapter(com);
        DataSet ds = new DataSet();
        da.Fill(ds);
        ddlCategoryBasedList.DataTextField = ds.Tables[0].Columns["CategoryBasedList"].ToString();
        ddlCategoryBasedList.DataSource = ds.Tables[0];
        ddlCategoryBasedList.DataBind();

        }
    protected void SqlDataSource1_Selecting(object sender, SqlDataSourceSelectingEventArgs e)
        {

        }
    public void populate()
    {
    string constr = ConfigurationManager.ConnectionStrings["CONN_STR"].ToString();
    SqlConnection con = new SqlConnection(constr);
    con.Open();
    SqlCommand com = new SqlCommand(" Select distinct(CategoryList) from Category", con);
    SqlDataAdapter da = new SqlDataAdapter(com);
    DataSet ds = new DataSet();
    da.Fill(ds);
    ddlListOfBooks.DataTextField = ds.Tables[0].Columns["CategoryList"].ToString();
    ddlListOfBooks.DataSource = ds.Tables[0];
    ddlListOfBooks.DataBind();
    }
}

The database structure of the above mentioned table - CATEGORY is as follows.

CREATE TABLE [dbo].[Category](
    [[CategoryBasedList]]] [varchar](100) NOT NULL,
    [CategoryList] [varchar](100) NOT NULL,
    [Authors] [varchar](100) NULL
) ON [PRIMARY]

GO

SET ANSI_PADDING OFF 
GO

Answer 1

Your slq tries to acces a column that is not there:

new SqlCommand(@"
Select distinct(CategoryBasedList) from Category 
where CategoryList = '" + (ddlListOfBooks.SelectedValue).ToString() + "'", con); 

check the columnname in the table Category : according to your DDL your DB-Column is named [CategoryBasedList] .

---

After fixing that, google Sql Injection and/or read Why do we always prefer using parameters in SQL statements? Use SqlParameters to supply parameters to your sql-statements.

---

Additionally you should start using using(var con = new SqlConnection(constr)) { ..... } to correctly dispose of your IDIsposable-Implementing DB-Objects in case they throw exceptions.

For pointers you can look here: in a "using" block is a SqlConnection closed on return or exception?

Answer 2

You need to sort out brackets around CategoryBasedList . As you show it now, field name is actually [CategoryBasedList]] , not as you might expect CategoryBasedList . Just rename that column name to remove extra brackets and you should be good to go.

Also, as already mentioned, you need to be aware about SQL Injections . Instead of constructing query by string concatination you need to use SQL Parameters