Build Master Detail (Expand Collapse) Windows Form DataGridView using C# and VB.Net

Hi satabeach,

The DataGridView does not support the expand / collapse (+/-).

You have to use DataGrid, which is replaced by the DataGridView.

The expand / collapse (+/-) buttons work only with two related DataTables in a DataSet.

Check this example. Now please take its reference and correct your code.

Database

For this example I have used of Northwind database that you can download using the link given below.

Download Northwind Database

Namespaces

C#

using System.Data;
using System.Data.SqlClient;

VB.Net

Imports System.Data
Imports System.Data.SqlClient

Code

C#

private void Form1_Load(object sender, EventArgs e)
{
    DataTable dtCategories = GetData("SELECT CategoryID AS Id,CategoryName AS Name,Description FROM Categories");
    DataTable dtProducts = GetData(@"SELECT CategoryID AS Id,ProductName AS Name,CAST(UnitPrice AS NUMERIC(18,2)) AS Price 
                                    FROM (SELECT *,ROW_NUMBER() OVER(PARTITION BY CategoryID ORDER BY ProductName DESC) AS Row_No FROM Products) 
                                    t WHERE Row_No <= 5");

    DataSet ds = new DataSet();
    ds.Tables.Add(dtCategories);
    ds.Tables.Add(dtProducts);
    DataRelation Datatablerelation = new DataRelation("Products", ds.Tables[0].Columns["Id"], ds.Tables[1].Columns["Id"], true);
    ds.Relations.Add(Datatablerelation);
    dataGrid1.DataSource = ds.Tables[0];
}

private DataTable GetData(string query)
{
    string conString = "Server=.;DataBase=Northwind;UID=sa;PWD=pass@123";
    using (SqlConnection con = new SqlConnection(conString))
    {
        using (SqlCommand cmd = new SqlCommand(query, con))
        {
            using (SqlDataAdapter sda = new SqlDataAdapter(cmd))
            {
                using (DataTable dt = new DataTable())
                {
                    sda.Fill(dt);

                    return dt;
                }
            }
        }
    }
}

VB.Net

Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
    Dim dtCategories As DataTable = GetData("SELECT CategoryID AS Id,CategoryName AS Name,Description FROM Categories")
    Dim dtProducts As DataTable = GetData("SELECT CategoryID AS Id,ProductName AS Name,CAST(UnitPrice AS NUMERIC(18,2)) AS Price 
                                            FROM (SELECT *,ROW_NUMBER() OVER(PARTITION BY CategoryID ORDER BY ProductName DESC) AS Row_No FROM Products) 
                                            t WHERE Row_No <= 5")
    Dim ds As DataSet = New DataSet()
    ds.Tables.Add(dtCategories)
    ds.Tables.Add(dtProducts)
    Dim Datatablerelation As DataRelation = New DataRelation("Products", ds.Tables(0).Columns("Id"), ds.Tables(1).Columns("Id"), True)
    ds.Relations.Add(Datatablerelation)
    dataGrid1.DataSource = ds.Tables(0)
End Sub

Private Function GetData(ByVal query As String) As DataTable
    Dim conString As String = "Server=.;DataBase=Northwind;UID=sa;PWD=pass@123"
    Using con As SqlConnection = New SqlConnection(conString)
        Using cmd As SqlCommand = New SqlCommand(query, con)
            Using sda As SqlDataAdapter = New SqlDataAdapter(cmd)
                Using dt As DataTable = New DataTable()
                    sda.Fill(dt)

                    Return dt
                End Using
            End Using
        End Using
    End Using
End Function

Screenshot

Note: Add the DataGrid control if not present to by right clicking the toolbar then Choose Items. From the .Net Framework Components tab add DataGrid.