How to Fill Comboboxes and Text Boxes Based on Multiple Combo Boxes Selected Values in C#

I have an SQL Table of Accounts[COA]. That Table has the following columns:

• [Bus Unit] - Combobox


• [BU Description] - TextBox


• [Obj] - Combobox


• [Obj Description] - TextBox


• [Sub] - Combobox


• [PEC] - TextBox

[Bus Unit] is bound to a combobox. A second combobox needs to be filled with [Obj] based on the [Bus Unit] combobox selected value and the third and final combobox needs to filled based on the [Obj] selected value. The remaining three columns are fields that need to populate text boxes based on the various selection of comboboxes.

For example: My [Bus Unit] combobox selected value is "10000". Now I need that selected index change to fill the [Obj] combobox with all the data associated with a [Bus Unit] of "10000". Not only that, but I also need it to fill a text box with [BU Description] that correlates directly with the [Bus Unit] of "10000".

The first two comboboxes will fill the following combobox as well as the following text box. The last combobox will fill the final textbox[PEC] as well as change the [Obj Description] text box if the value has changed.

I am struggling to figure out how to do all this. The following is what I have so far:

    public void bindBusUnitToComboboxes()
    {
        SqlConnection cs = new SqlConnection(@"Data Source=MARYANNEBORJA\SQLEXPRESS;Initial Catalog=jdeDatabase;Persist Security Info=True;User ID=Jordan;Password=*******");
        SqlDataAdapter daBU = new SqlDataAdapter("SELECT DISTINCT [Bus Unit] FROM COA", cs);

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

        for (int i = 0; i < dt.Rows.Count; i++)
        {
            bus_UnitComboBox.Items.Add(dt.Rows[i]["Bus Unit"]);
        }

        bus_UnitComboBox.DisplayMember = "Bus Unit";
        bus_UnitComboBox.SelectedIndex = 0;

    }

    private void bus_UnitComboBox_SelectedIndexChanged(object sender, EventArgs e)
    {

        if (bus_UnitComboBox.SelectedItem != null)
        {
            dv = jDEDatabaseDataSet.Tables[2].DefaultView;
            dv.RowFilter = "[Bus Unit] = '" + bus_UnitComboBox.SelectedItem + "'"; 
            objComboBox.DataSource = dv;
            objComboBox.DisplayMember = "Obj";
            objComboBox.ValueMember = "Obj";

            using (SqlConnection connection = new SqlConnection(@"Data Source=MARYANNEBORJA\SQLEXPRESS;Initial Catalog=jdeDatabase;Persist Security Info=True;User ID=Jordan;Password=*******"))
            {
                SqlCommand command =
                new SqlCommand("SELECT * FROM [COA] WHERE [Bus Unit]='" + bus_UnitComboBox.Text + "'", connection);
                connection.Open();

                SqlDataReader read = command.ExecuteReader();

                while (read.Read())
                {
                   bU_DescriptionTextBox.Text = (read["BU Description"].ToString());
                }
                read.Close();
            }
        }
        else { MessageBox.Show("Something is happening when you try to bind data to BUS UNIT COMBOBOX"); }

    }

    private void objComboBox_SelectedIndexChanged(object sender, EventArgs e)
    {

            dv = jDEDatabaseDataSet.Tables[2].DefaultView;
            dv.RowFilter = "[Bus Unit] = '" + bus_UnitComboBox.SelectedItem + "' AND [Obj] ='" + objComboBox.Text + "'";
            subComboBox.DataSource = dv;
            subComboBox.DisplayMember = "Sub";
            subComboBox.ValueMember = "Sub";

            using (SqlConnection connection = new SqlConnection(@"Data Source=MARYANNEBORJA\SQLEXPRESS;Initial Catalog=jdeDatabase;Persist Security Info=True;User ID=Jordan;Password=*******"))
            {
                SqlCommand command =
                new SqlCommand("SELECT * FROM [COA] WHERE [Obj]='" + objComboBox.Text + "'", connection);
                connection.Open();

                SqlDataReader read = command.ExecuteReader();

                while (read.Read())
                {
                    obj_DescriptionTextBox.Text = (read["Obj Description"].ToString());
                }
                read.Close();
            }

    }

    private void subComboBox_SelectedIndexChanged(object sender, EventArgs e)
    {

            using (SqlConnection connection = new SqlConnection(@"Data Source=MARYANNEBORJA\SQLEXPRESS;Initial Catalog=jdeDatabase;Persist Security Info=True;User ID=Jordan;Password=*******"))
            {
                SqlCommand command = new SqlCommand("SELECT * FROM [COA] WHERE [Bus Unit]='" + bus_UnitComboBox.Text + "' AND [Obj] ='" + objComboBox.Text + "'AND [Sub] ='" + subComboBox.Text + "'");
                command.Connection = connection;
                connection.Open();

                SqlDataReader read = command.ExecuteReader();

                while (read.Read())
                {

                    if (!read.IsDBNull(8))
                    {
                        pECTextBox.Text = read.GetString(8);
                    }
                    else
                    {
                        pECTextBox.Text = "";
                    }

                    obj_DescriptionTextBox.Text = (read["Obj Description"].ToString());
                }
                read.Close();
            }

    }

I am able to bind the [Obj] combobox and [Sub] combobox. The problem is that when I select a value in the [Obj] combobox it does not fill the [Obj Description] Textbox with the correct value every time. I have the same problem with the [Sub] Combobox trying to change the value of the [Obj Description] Textbox.