Do I still need to use .Open() and .Close() if I already use using statement in C#?

I’m new with Npgsql, my C# Code like below:

Do I still need to use:

conn.Open();
conn.Close();

if I already use using statement?, I have try to remove it but nothing happen.

        try
        {
            using (NpgsqlConnection conn = new NpgsqlConnection(Models.AppSettings.PG_SQL.Connection_String))
            {
                conn.Open();  // do I still need this?, I remove it, but it still working properly

                try
                {
                   string sql = "Select * From mytable1"

                    using (var dr = conn.ExecuteReader(sql, new { } ))
                    {
                        if (dr.Read())
                        {
                            // do some process
                        }
                    }
                }
                catch (Exception e)
                {
                    Helper.SaveLogAsync("Learning.Test: " + e.ToString(), Models.Errs.ErrType.Err);
                }
                finally { }

                conn.Close(); // do I still need this?, I remove it, but it still working properly
            }

        }
        catch (Exception e)
        {
            Helper.SaveLogAsync("Learning.Test: " + e.ToString(), Models.Errs.ErrType.Err);
        }
        finally { }

>Solution :

Yes, you can safely remove conn.Open() and conn.Close() when using a using statement in C#. The using statement ensures that the Dispose() method is called on the NpgsqlConnection object when the block is exited, which takes care of closing the connection.

Your code without conn.Open() and conn.Close() calls:

try
{
    using (NpgsqlConnection conn = new NpgsqlConnection(Models.AppSettings.PG_SQL.Connection_String))
    {
        try
        {
            string sql = "Select * From mytable1";

            using (var dr = conn.ExecuteReader(sql, new { }))
            {
                if (dr.Read())
                {
                    // do some process
                }
            }
        }
        catch (Exception e)
        {
            Helper.SaveLogAsync("Learning.Test: " + e.ToString(), Models.Errs.ErrType.Err);
        }
    }
}
catch (Exception e)
{
    Helper.SaveLogAsync("Learning.Test: " + e.ToString(), Models.Errs.ErrType.Err);
}

In this case, you don’t need to explicitly call conn.Open() because the ExecuteReader method will automatically open the connection if it’s not already open. Similarly, you don’t need to call conn.Close() because the using statement takes care of disposing the connection, which includes closing it.