How to update .mdb files with a C# web application?

Question

Hi, 


I am writing a app that must have the ability to :


 - GUI should be seen on a web interface (Thus I'm using C# Web Application)
 - Be able to select .mdb files
 - Add rows
 - Delete rows
 - Edit rows
 - Save everything back to the .mdb file.


I have googled for ages.


I have written a similar application in a normal C# windows form application, I used OLEdb to do everything and it worked fine, it wasn't restricted to only one .mdb file.


In the C# Windows Form app I used Gridview control.
As the Web Application doesn't have Gridview, I used a datagrid.


Here is the code is have so far : 

    public partial class _Default : System.Web.UI.Page

    {

        string databasePath = "____________.mdb";

        DataTable userTable = new DataTable();

        OleDbDataAdapter adapter;

        OleDbConnection connection;

        OleDbCommand command;

        OleDbCommandBuilder builder;

        DataSet ds;

        DataSet tempDs;

        public string DatabaseName = null;

        string connectionString = "Provider=Microsoft.Jet.OLEDB.4.0; Data Source=";

        protected void Page_Load(object sender, EventArgs e)

        {

            tbDatabasePath.Text = databasePath;

        }

        protected void btnLoadData_Click(object sender, EventArgs e)

        {

            ReadRecords();

        }

        protected void btnGetTables_Click(object sender, EventArgs e)

        {

            try

            {

                ddTables.Items.Clear();

                ddTables.Text = null;

                getTables();

            }

            catch (Exception ex)

            {

                ClientScript.RegisterStartupScript(this.GetType(), "myalert", "alert('Could not retrieve the Tables');", true);

            }

        }

        private void getTables()

        {

            string tempstring = "";

            string getTConnection = connectionString + databasePath; ;

            OleDbConnection myConnection = new OleDbConnection(getTConnection);

            myConnection.Open();

            DataTable datT = myConnection.GetSchema("Tables");

            for (int i = 0; i < datT.Rows.Count; i++)

            {

                tempstring = datT.Rows[i][2].ToString();

                if (tempstring.Contains("MSys"))

                {

                }

                else

                {

                    ddTables.Items.Add(datT.Rows[i][2].ToString());

                }

            }

            myConnection.Close();

        }

        private void ReadRecords()

        {

            datagrid.DataSource = null;

            OleDbDataReader reader = null;

            try

            {

                connection = new OleDbConnection("Provider=Microsoft.Jet.OLEDB.4.0; " + "Data Source=" + databasePath);

                OleDbCommand cmd = new OleDbCommand("Select * FROM " + ddTables.Text, connection);

                adapter = new OleDbDataAdapter(cmd);

                builder = new OleDbCommandBuilder(adapter);

                ds = new DataSet("MainDataSet");

                tempDs = new DataSet("TempDataSet");

                connection.Open();

                adapter.Fill(tempDs);

                tempDs.Clear();

                tempDs.Dispose();

                adapter.Fill(ds, ddTables.Text);

                userTable = ds.Tables[ddTables.Text];

            }

            catch

            {

                ClientScript.RegisterStartupScript(this.GetType(), "myalert", "alert('Could not load the data');", true);

            }

            finally

            {

                if (reader != null) reader.Close();

                //if (connection != null) connection.Close();

                datagrid.ShowFooter = true;

            }

            CreateTempTable(0, 10);

            ClientScript.RegisterStartupScript(this.GetType(), "myalert", "alert('DONE');", true);

        }

        private void ReadRecords2()

        {

           // datagrid.DataSource = null;

         

            OleDbDataReader reader = null;

            try

            {

                connection = new OleDbConnection("Provider=Microsoft.Jet.OLEDB.4.0; " + "Data Source=" + databasePath);

                OleDbCommand cmd = new OleDbCommand("Select * FROM " + ddTables.Text, connection);

                adapter = new OleDbDataAdapter(cmd);

                builder = new OleDbCommandBuilder(adapter);

                ds = new DataSet("MainDataSet");

                tempDs = new DataSet("TempDataSet");

                connection.Open();

                adapter.Fill(tempDs);

                tempDs.Clear();

                tempDs.Dispose();

                adapter.Fill(ds, ddTables.Text);

                userTable = ds.Tables[ddTables.Text];

            }

            catch

            {

                ClientScript.RegisterStartupScript(this.GetType(), "myalert", "alert('Could not load the data');", true);

            }

            finally

            {

                if (reader != null) reader.Close();

                //if (connection != null) connection.Close();

            }

            CreateTempTable(0, 10);

            ClientScript.RegisterStartupScript(this.GetType(), "myalert", "alert('DONE');", true);

        }

        private void CreateTempTable(int startRecord, int noOfRecords)

        {

            try

            {

                userTable.Rows.Clear();

                adapter.Fill(ds, "");

                userTable = ds.Tables[""];

            }

            catch (Exception ex)

            {

                ClientScript.RegisterStartupScript(this.GetType(), "myalert", "alert('Could not load the data in  CreateTempTable');", true);

            }

            datagrid.DataSource = userTable.DefaultView;

            datagrid.DataBind();

        }

        protected void datagrid_RowEditing(object sender, GridViewEditEventArgs e)

        {

            datagrid.EditIndex = e.NewEditIndex;

            ReadRecords();

         

        }

        protected void datagrid_SelectedIndexChanged(object sender, EventArgs e)

        {

        }

        protected void datagrid_RowUpdated(object sender, GridViewUpdatedEventArgs e)

        {

            adapter.Update(userTable);

        }

        protected void datagrid_RowUpdating(object sender, GridViewUpdateEventArgs e)

        {

           

            adapter.Update(userTable);

            ReadRecords();

        }

        protected void datagrid_RowCancelingEdit(object sender, GridViewCancelEditEventArgs e)

        {

           datagrid.EditIndex = -1;

           ReadRecords();

        }

        protected void datagrid_RowDeleting(object sender, GridViewDeleteEventArgs e)

        {

            int rowToDelete = e.RowIndex;

            datagrid.DeleteRow(rowToDelete);

            adapter.Update(userTable);

            ReadRecords();

        }

    }

}

It can : 


 - get the .mdb file
 - get the tables in the file and display it
 - read the data out of the selected table and display it in the gridview
 - add the edit delete buttons


Now when I click the edit button, it makes the selected row editable.
But when I click the update button I get "Object reference not set to an instance of an object."
The code worked in the Forms application.. 


Is there any way the adapter.Update(userTable); will be able to work the same it worked in the forms application?


Can anybody please help me see my problem. If I can only get it to save the changes back to the .mdb file I would be extremely glad.