Hello everyone,

In the last few days I was trying to create a DataGridView that shows

data from two tables related with a foreign key constraint. The

DataGridView should have 2 columns. The first one, called 'Name' is a

bounded column that gets data from the first table and the second

column is an unbounded one of DataGridViewComboBoxColumn type that

shows 'details' from the second table. This is a classic example of,

lets say, region-city data binding. The DataGridView is formed by a

number of regions (each region represents one row in the grid) and for

each region a combo box shows the cities from that region...

I've tried the examples from MSDN and even the given examples, but with

no success... The error I get is: "DataGridViewComboBox cell value is

not valid".

The code should talk for itself:

---

using System;

using System.Collections.Generic;

using System.ComponentModel;

using System.Data;

using System.Data.SqlClient;

using System.Drawing;

using System.Text;

using System.Windows.Forms;

namespace nradatagridview

{

public partial class Form1 : Form

{

DataSet dsArticle;

BindingSource bsArticleSource;

DataGridView dgArticleGrid;
public Form1()

{

InitializeComponent();

}

private void Form1_Load(object sender, EventArgs e)

{

dsArticle = LoadDBData();

bsArticleSource = new BindingSource(dsArticle, "Articles");

InitializeGrid();

}

private void InitializeGrid()

{

dgArticleGrid = new DataGridView();

dgArticleGrid.Name = "MasterGrid";

dgArticleGrid.MultiSelect = false;

dgArticleGrid.AutoGenerateColumns = false;

dgArticleGrid.DataSource = bsArticleSource;

dgArticleGrid.AllowUserToAddRows = false;

dgArticleGrid.SelectionMode = DataGridViewSelectionMode.FullRowSelect;

dgArticleGrid.AlternatingRowsDefaultCellStyle.BackColor =

SystemColors.InactiveCaptionText;

dgArticleGrid.Dock = DockStyle.Fill;

dgArticleGrid.VirtualMode = true;

//Name (ID) column (textbox)

DataGridViewTextBoxColumn colGestID = new DataGridViewTextBoxColumn();

colGestID.Name = "colGestID";

colGestID.DataPropertyName = "RegionName";

colGestID.HeaderText = "Region";

//colName.AutoSizeMode = DataGridViewAutoSizeColumnMode.DisplayedCells;

colGestID.ReadOnly = false;

dgArticleGrid.Columns.Add(colGestID);

//Details (combobox)

DataGridViewComboBoxColumn colCombo = new DataGridViewComboBoxColumn();

colCombo.Name = "colCombo";

colCombo.HeaderText = "ComboTest";

BindingSource bs = new BindingSource();

bs.DataSource = bsArticleSource;

bs.DataMember = "FK_Relation";

colCombo.DataSource = bs;

colCombo.DataPropertyName = "SelectedCityName"; //the exception is

trown here, why?

colCombo.DisplayMember = "CityName";

colCombo.ValueMember = "CityName";

colCombo.ReadOnly = false;

colCombo.AutoSizeMode =

DataGridViewAutoSizeColumnMode.None;

dgArticleGrid.Columns.Add(colCombo);

this.Controls.Add(dgArticleGrid);

}

private DataSet LoadDBData()

{

try

{

DataSet ds = new DataSet();

using (SqlConnection conn = new SqlConnection("Data Source=BLA;Initial

Catalog=BLA;User ID=BLA"))

{

conn.Open();

SqlCommand cmd = new SqlCommand();

cmd.CommandText = "select * from

regions";

cmd.Connection = conn;

using (SqlDataReader drArticles = cmd.ExecuteReader())

{

ds.Load(drArticles, LoadOption.OverwriteChanges, new string[] {

"Regions" });

}

//cmd.CommandText = "select * from cities";

using (SqlDataReader drGest = cmd.ExecuteReader())

{

ds.Load(drGest, LoadOption.OverwriteChanges, new string[] { "Cities" });

}

ds.Relations.Add(new

DataRelation("FK_Relation",ds.Tables["Regions"].Columns["ID"],ds.Tables["Cities"].Columns["RegionID"]));
conn.Close();

}

return ds;

}

catch (Exception e)

{

MessageBox.Show(e.ToString());

return null;

}

}

}

}

}

}

---

The table structure looks like this:

Region Table:

ID,RegionName,.....,SelectedCityName

City Table:

ID,RegionID,CityName,...