private DbProviderFactory Factory = null;
        private string ProviderName = "ODBC";
        private string ConnectionString = "...";
        
        public void AnyMethodPublic()
        {
            Factory = System.Data.Common.DbProviderFactories.GetFactory(ParseProviderName(ProviderName));
            DbDataAdapter adapter = Factory.CreateDataAdapter();
            DataSet ds = AnyMethodPrivate(adapter);
        }
      
        private DataSet AnyMethodPrivate(IDbDataAdapter adapter)
        {
            DataSet ds = new DataSet();
            using (DbConnection connection = Factory.CreateConnection())
            {
                connection.ConnectionString = ConnectionString;
                try
                {
                    connection.Open();
                    using (DbCommand command1 = Factory.CreateCommand())
                    {
                        command1.Connection = connection;
                        command1.CommandText = "SELECT * FROM one";
                        adapter.SelectCommand = command1;

                        (adapter as DbDataAdapter).Fill(ds, "one");
                    }
                    using (DbCommand command2 = Factory.CreateCommand())
                    {
                        command2.Connection = connection;
                        command2.CommandText = "SELECT * FROM two";
                        adapter.SelectCommand = command2;
                        (adapter as DbDataAdapter).Fill(ds, "two");
                    }
                    return ds;
                }
                catch (DbException)
                {
                    return null;
                }
            }
        }

        private static string ParseProviderName(string name)
        {
            DataTable dt = DbProviderFactories.GetFactoryClasses();
            List<string> providers = new List<string>();
            foreach (DataRow row in dt.Rows)
            {
                providers.Add(row["InvariantName"].ToString());
            }
            foreach (string provider in providers)
            {
                if (Regex.IsMatch(provider, name, RegexOptions.IgnoreCase))
                    return provider;
            }
            throw new ApplicationException(String.Format("Провайдер {0} не найден", name));
        }

public sealed class OleDbDataAdapter : DbDataAdapter, IDbDataAdapter, IDataAdapter, ICloneable

public sealed class SqlDataAdapter : DbDataAdapter, IDbDataAdapter, IDataAdapter, ICloneable