Adding, Updating and Deleting in the grid box - NOT THE NORMAL WAY!

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Gridview

database

DataGridView

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I am making an admin main page for my website.
It contains a drop down box that should retrieve the name of all the tables in the db.
When a table is selected, the contents of it should be displayed in the grid box.
Once the contents are displayed a user can update/edit/add/delete using the same grid box.

Currently I have the data entered in grid box manually that contains name of each and every table.
Also when a user selects a table, the contents are displayed in the grid box using following code:

protected void ddSelectTable_SelectedIndexChanged(object sender, EventArgs e)
        {


            SqlConnection conn = new SqlConnection();
            conn = new SqlConnection("Data Source=.\\sqlexpress;Initial Catalog=OCBF;Integrated Security=True");

            conn.Open();
            SqlCommand cmd = new SqlCommand();
            //cmd.Parameters.AddWithValue("selectedValue", Convert.ToString(ddSelectTable.SelectedValue));
            sqlquery = "select * from " + Convert.ToString(ddSelectTable.Text);


            cmd.Connection = conn;

            cmd.CommandText = sqlquery;
            cmd.CommandType = CommandType.Text;
            SqlDataAdapter da = new SqlDataAdapter(cmd);

            DataTable dt = new DataTable();
            da.Fill(dt);


            gvData.DataSource = dt;
            gvData.DataBind();

            conn.Close();

        }

-------------------
THE PROBLEM ARISES WHEN I TRY TO UPDATE OF DELETE ANYTHING.
I have business logic where the variables are defined.

The main data for edit/update/add is in Data Access Class where the select/edit functions are defined.

And below is the code of the actual page: It has a drop down box, a grid box and a button.

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

public partial class Masters_CategoryMaster : System.Web.UI.Page
{

    #region Variables

    clsDACategory objDACategory;
    clsBOCategory objBOCategory;
    

    #endregion

    void FillGrid()
    {
        gvCategory.DataSource = new clsDACategory().select();
        gvCategory.DataBind();
    }

    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            FillGrid();

        }
    }
    protected void gvCategory_RowEditing(object sender, GridViewEditEventArgs e)
    {
        gvCategory.EditIndex = e.NewEditIndex;
        FillGrid();

    }
    protected void gvCategory_RowUpdating(object sender, GridViewUpdateEventArgs e)
    {
        objBOCategory = new clsBOCategory();
        objBOCategory.CategoryID=Convert.ToInt32(((Label)gvCategory.Rows[e.RowIndex].Controls[1].Controls[1]).Text); //typecasting - converting control to label
        objBOCategory.CategoryName = ((TextBox)gvCategory.Rows[e.RowIndex].FindControl("txtCategoryNameEdit")).Text;

        if (new clsDACategory().update(objBOCategory) > 0)
        {
            Response.Write("Updated Successfully!");
            gvCategory.EditIndex = -1; // it'll make edit option disable and blocked for any further change.
            FillGrid();
        }
        else
        {
            Response.Write("Updation failed");
        }
    }
    protected void gvCategory_RowCancelingEdit(object sender, GridViewCancelEditEventArgs e)
    {
        gvCategory.EditIndex = -1;
        FillGrid();
    }
    protected void btnAdd_Click(object sender, EventArgs e)
    {
        if (btnAdd.Text.Equals("Add"))
        {
            gvCategory.FooterRow.Visible = true; //a text box gets visible in footer side of the grid box. by default its hidden.
            btnAdd.Text = "Save";
        }
        else
        {
            objDACategory = new clsDACategory();
            objBOCategory = new clsBOCategory();

            objBOCategory.CategoryName = ((TextBox)gvCategory.FooterRow.FindControl("txtCategoryNameAdd")).Text;
            if (objDACategory.insert(objBOCategory) > 0)
            {
                Response.Write("Inserted Succesfully");
                FillGrid();
                btnAdd.Text = "Add";
            }
            else {
                Response.Write("Insertion Failed");
            }

        }
    }
}

---------------------------


Note : The above coding is only for one single table named as CategoryMaster.

I need serious quick help on getting this logic to work with the proper coding as I have invested a week after this and not reaching any conclusion.