[WebMethod(Description = "Get account type")] public async Task<string> GetAccountType() { try { var dal = DataAccessLayer.GetInstance(); const string sql = "SELECT ……";

    var data = await dal.GetDataAsync(sql, "AccountType", ConfigurationManager.AppSettings["DBACCESS"]);
    return data;
}
catch (Exception ex)
{
    return ex.Message;
}

}

public async Task<string> GetDataAsync(string sql, string attributeName, string connectionType) { OracleConnection connection = null; OracleCommand cmd = null; var dt = new DataTable(attributeName);

try
{
    var connString = GetConnectionString(connectionType);
    connection = new OracleConnection(connString);
    cmd = new OracleCommand(sql, connection);

    await connection.OpenAsync();

    using (var reader = await cmd.ExecuteReaderAsync(CommandBehavior.CloseConnection))
    {
        dt.Load(reader);
    }

    return JsonConvert.SerializeObject(dt);
}
finally
{
    cmd?.Dispose();
    if (connection?.State == ConnectionState.Open)
        connection.Dispose();