C#

string sConnection = "Data Source=127.0.0.1,1433;Persist Security Info=True;Initial Catalog=GMAO;User ID=sa;Password=sa";
string sSQL = "SELECT ID, com FROM energie";

SqlConnection conn = new SqlConnection(sConnection);
SqlCommand comm = new SqlCommand(sSQL, conn);
SqlDataAdapter da = new SqlDataAdapter(comm);

try
{
    DataSet ds = new DataSet();

    comm.Connection.Open();
    
    da.Fill(ds);
    
    comboBox1.DataSource = da.Table[0];
    comboBox1.DisplayMember = "com";
    comboBox1.ValueMember = "ID";
}
catch (SqlException ex)
{
    MessageBox.Show(ex.Message);
}
finally
{
    comm.Connection.Close();
}

public static OleDbDataReader GetAll(OleDbConnection conn, bool status)
        {
            try
            {
                string query =
                    "SELECT [Id], [Name], [CreatedDate], [CreatedBy], " +
                    "   [UpdatedDate], [UpdatedBy] " +
                    "FROM [Role] " +
                    "WHERE [Status] = @pStatus " +
                    "ORDER BY [Name] ASC";

                OleDbCommand cmd = new OleDbCommand(query, conn);
                OleDbParameter pStatus = cmd.Parameters.Add("@pStatus", 
                    OleDbType.Boolean);
                pStatus.Value = status;
                OleDbDataReader dr = cmd.ExecuteReader();

                return dr;
            }
            catch (OleDbException ex)
            {
                throw new Exception("OleDb Error: " + ex.Message);
            }
            catch (Exception ex)
            {
                throw ex;
            }
        }

public List<Role> GetAll(bool status)
        {
            List<Role> listRole = new List<Role>();

            try
            {
                if (conn.State != ConnectionState.Open)
                {
                    conn.Open();
                }

                OleDbDataReader dr = RoleData.GetAll(conn, status);

                if (dr.HasRows)
                {
                    while (dr.Read())
                    {
                        Role role = new Role();
                        role.Id = int.Parse(dr["Id"].ToString());
                        role.Name = dr["Name"].ToString();
                        role.CreatedBy = dr["CreatedBy"].ToString();
                        role.CreatedDate = (string.Empty.Equals(dr["CreatedDate"].ToString()) ?
                            DateTime.MinValue :
                            DateTime.Parse(dr["CreatedDate"].ToString()));
                        role.UpdatedBy = dr["UpdatedBy"].ToString();
                        role.UpdatedDate = (string.Empty.Equals(dr["UpdatedDate"].ToString()) ? 
                            DateTime.MinValue : 
                            DateTime.Parse(dr["UpdatedDate"].ToString()));
                        listRole.Add(role);
                    }
                }

                return listRole;
            }
            catch (OleDbException ex)
            {
                throw new Exception("OleDb Error: " + "\n" + ex.Message);
            }
            catch (Exception e)
            {
                throw new Exception(e.Message);
            }
            finally
            {
                conn.Close();
            }
        }