SQLBulkCopy Oracle到SQL Guid錯誤

執行SqlBulkCopy將200k +記錄從Oracle移動到SQL。在執行WriteToServer時遇到將字符串轉換為guid的錯誤。在Oracle中，表將guid保存為nvarchar（50）; SQL它是一個唯一的標識符。 sql語句沒有什麼特別之處 - 只需從Oracle源表中選擇所有數據。

public void BulkCopyFromOrl(OracleDataReader rdr, string targetTableName) 
{
    // open Sql connection
    var _con = GetConnection();

    // Sql Bulk Copy instance
    var _bc = new SqlBulkCopy(_con);

    // set destination table
    _bc.DestinationTableName = targetTableName;

    // set batch size (optional)
    _bc.BatchSize = 10000;

    // set time out (optional)
    _bc.BulkCopyTimeout  = 600;

    // write to server
    _bc.WriteToServer(rdr);

    // close and dispose
    _bc.Close();

    // close and dispose
    Terminate(null, _con);
}

public SqlDataReader GetSourceData(string tableName)
{
    // todo: should be parameterized but for demonstration in the console app, 
    // just add columns and table name 
    var sql = string.Format("SELECT {0} FORM {1}", MappedColumns(), tableName);
    return ExecuteReader(sql);
}