Question

I have a Combobox to fill the data for City, State and PinCode
these combobox is dopdown list and the user will pick it.

and it loads once the form opens.

Here is the CODE:

            /// CODE TO BRING A DATA FROM SQL INTO THE FORM DROP LIST

            /// To fill the sates from States Table

            cn = new SqlConnection(@"Data Source=Nick-PC\SQLEXPRESS;Initial Catalog=AutoDB;Integrated Security=True");
            cmd= new SqlCommand("select * from TblState",cn);
            cn.Open();
            SqlDataReader dr;

            try
            {
                dr = cmd.ExecuteReader();
                while (dr.Read())

                {
                    SelectState.Items.Add(dr["State"].ToString());
                }

            }

            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }

            finally
            {
                cn.Close();
            }

            //To fill the Cities from City Table

            cn1 = new SqlConnection(@"Data Source=Nick-PC\SQLEXPRESS;Initial Catalog=AutoDB;Integrated Security=True");
            cmd1 = new SqlCommand("SELECT * FROM TblCity", cn);
            cn.Open();
            SqlDataReader ds;

            try
            {
                ds = cmd1.ExecuteReader();
                while (ds.Read())
                {
                    SelectCity.Items.Add(ds["City"].ToString());
                }

            }

            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }

            finally
            {
                cn1.Close();
            }

            // To fill the Data in the Pincode from the City Table
            cn2 = new SqlConnection(@"Data Source=Nick-PC\SQLEXPRESS;Initial Catalog=AutoDB;Integrated Security=True");
            cmd2 = new SqlCommand("SELECT (Pincode) FROM TblCity ", cn2);
            cn2.Open();
            SqlDataReader dm;

            try
            {
                dm = cmd2.ExecuteReader();
                while (dm.Read())
                {
                    SelectPinCode.Items.Add(dm["Pincode"].ToString());
                }

            }

            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }

            finally
            {
                cn2.Close();
            }

its kinda Big, i am doing the same steps for all the combo-box, but is there a way i can merge it in a simple way.

Answer 1

The stick-to-the-basics approach – refactor your code into a single method.

static IEnumerable<string> Load(string tableName, string columnName)
{
    List<string> result = new List<string>();

    try
    {
        using (var cn = new SqlConnection(@"Data Source=Nick-PC\SQLEXPRESS;Initial Catalog=AutoDB;Integrated Security=True"))
        {
            cn.Open();
            using (var cmd = new SqlCommand("SELECT * FROM " + tableName, cn))
            {
                using (var reader = cmd.ExecuteReader())
                {
                    while (reader.Read())
                    {
                        result.Add(reader[columnName].ToString());
                    }
                }
            }
        }
    }
    catch (Exception ex)
    {
        MessageBox.Show(ex.Message);
    }

    return result;
}

Crude assumptions made:

1. Only querying 1 table, 1 column.
2. Not checking for nulls on the IDataReader.