Saving data in a Database C# WPF [duplicate]

This is my first time using Databases so maybe I am missing something but my Database is not being updated.

I have created a Database in Visual Studio named MainAreas with two columns: MainAreaId (primary key) and MainAreaName(string).

In my application the user adds, deletes and updates main areas and I want to save this information in the database so when the program is closed and opened again the main areas added previously are still there.

The design I´ve done is the following (this part may not be the more appropiate solution, I accept advice): I have created a class called DatabaseConnection which connects to the Database, and a class called RoomsDatabaseHandler which updates the database with the MainAreas added in the AreasUserControl (see attached diagram):Class diagram

At the moment I have implemented a function that adds a new row in the MainAreas Table of the database and a function that retrieves all the MainAreas in the MainAreas table when starting up the application. But this doesn´t work.

This is my DatabaseConnection class:

class DatabaseConnection
{
    private string sql_string;
    private string strCon;
    private System.Data.SqlClient.SqlDataAdapter da_1;

    public string Sql
    {
        set { sql_string = value; }
    }

    public string connection_string
    {
        set { strCon = value; }
    }

    public System.Data.DataSet GetConnection
    {
        get 
        { return MyDataSet();}
    }
    public void UpdateDatabase(System.Data.DataSet ds)
    {
        System.Data.SqlClient.SqlCommandBuilder cb = new System.Data.SqlClient.SqlCommandBuilder(da_1);
        cb.DataAdapter.Update(ds.Tables[0]);
    }

    private System.Data.DataSet MyDataSet()
    {
        System.Data.SqlClient.SqlConnection con = new System.Data.SqlClient.SqlConnection(strCon);

        da_1 = new System.Data.SqlClient.SqlDataAdapter(sql_string, con);
        System.Data.DataSet dat_set = new System.Data.DataSet();
        da_1.Fill(dat_set, "MainAreas");
        //da_1.Fill(dat_set);
        con.Close();

        return dat_set;

    }
}

This is my RoomsDatabaseHandler class:

public class RoomsDatabaseHandler
{
    DatabaseConnection objConnect;
    string conString;

    DataSet ds;
    DataRow dRow;

    public RoomsDatabaseHandler()
    {
        objConnect = new DatabaseConnection();
        conString = Properties.Settings.Default.MyDatabaseConnectionString;

        objConnect.connection_string = conString;
        objConnect.Sql = Properties.Settings.Default.SQL;

        ds = objConnect.GetConnection;
    }
    public void AddNewMainArea(string mainAreaName)
    {
        DataRow row = ds.Tables[0].NewRow();
        row[0] = ds.Tables[0].Rows.Count;
        row[1] = mainAreaName;

        ds.Tables[0].Rows.Add(row);

        try
        {
            objConnect.UpdateDatabase(ds);
            MessageBox.Show("Database updated", "OK",
                    MessageBoxButton.OK, MessageBoxImage.Information);
        }
        catch(Exception err)
        {
            MessageBox.Show(err.Message);
        }
    }
    public List<string> LoadMainAreas()
    {
        List<string> mainAreasList = new List<string>();

        for (int it = 0; it < ds.Tables[0].Rows.Count; it++ )
        {
            dRow = ds.Tables[0].Rows[it];
            mainAreasList.Add(dRow.ItemArray.GetValue(1).ToString());
        }

        return mainAreasList;
    }
}

Could you please give me a hand on what´s wrong here? When the user adds a new main Area, the message box "Database updated" is shown but if I have a look to the MainAreas table data in the Server Explorer I cannot see any row added. And when I restart the application, and the LoadMainAreas method is called, the table looks empty.

Thanks in advance!! And sorry for the long text.