后裔中的 For 循环（序列不包含元素）c#

Question

我有一个复杂的 XML 文件，我想从特定的事务标签中检索值。最后，我需要将这些值保存到 CSV 文件中。

我正在尝试在它所在的每个事务标签中检索下面的值。

<szCustomerID>2988880562567</szCustomerID>

   <szCustomerName>130808125028SHM </szCustomerName>

   <szExternalID>3177@06/07/17</szExternalID>

注意所有的交易标签都不一样
不幸的是，它正在循环所有事务标签，我得到错误序列不包含元素

有没有一种方法可以让我循环使用后代并总是跳过第二个交易标签，因为我不需要它

  try
        {
            string strSource_voucher = @"C:\\TempFid";

                  string[] files = Directory.GetFiles(strSource_voucher, "*.xml", SearchOption.AllDirectories);

            if (files.Length > 0) // Check if files has values
            {
                StringBuilder dataToBeWritten = new StringBuilder();


                foreach (string file in files)
                {

                    dataToBeWritten.Append("szCustomerID");
                    dataToBeWritten.Append(",");
                    dataToBeWritten.Append("szCustomerName");
                    dataToBeWritten.Append(",");
                    dataToBeWritten.Append("szExternalID");
                    dataToBeWritten.Append(",");

                    dataToBeWritten.Append(Environment.NewLine);

                    XDocument xDocument = XDocument.Load(file);


                    int results = xDocument.Descendants("Transaction").Count();

                    foreach (var trans in xDocument.Descendants("Transaction"))

                    {
                           //var trans = xDocument.Descendants("Transaction");

                           var val1 = (string)trans.Descendants("Set").Elements("szCustomerID").First();

                            var val2 = (string)trans.Descendants("Set").Elements("szCustomerName").First();


                            var val3 = (string)trans.Descendants("Set").Elements("szExternalID").First();

                            dataToBeWritten.Append(val1);
                            dataToBeWritten.Append(",");

                            dataToBeWritten.Append(val2);
                            dataToBeWritten.Append(",");

                            dataToBeWritten.Append(val3);
                            dataToBeWritten.Append(",");

                            dataToBeWritten.Append(Environment.NewLine);


                    } // End of For each var trans


                    Console.WriteLine(dataToBeWritten.ToString());

                    Console.ReadLine();

Answer 1

您可以使用Element 代替Elements 并检查该值是否不是null

foreach (var trans in xDocument.Descendants("Transaction"))
{
    XElement setElement = trans.Descendants("Set").FirstOrDefault();
    if (setElement != null)
    {
        var val1 = (string)setElement.Element("szCustomerID");
        var val2 = (string)setElement.Element("szCustomerName");
        var val3 = (string)setElement.Element("szExternalID");

        if (val1 != null && val3 != null && val3 != null)
        {
            dataToBeWritten.Append(val1);
            dataToBeWritten.Append(",");

            dataToBeWritten.Append(val2);
            dataToBeWritten.Append(",");

            dataToBeWritten.Append(val3);
            dataToBeWritten.Append(",");

            dataToBeWritten.Append(Environment.NewLine);
        }
    }
}

Answer 2

只需使用for 循环并将i 增加2，如下所示：

var transactions = xDocument.Descendants("Transaction").ToList();
for (int i = 0; i < transactions.Count(); i += 2)
{

    //var trans = xDocument.Descendants("Transaction");
    var val1 = (string)transactions[i].Descendants("Set").Elements("szCustomerID").First();
    var val2 = (string)transactions[i].Descendants("Set").Elements("szCustomerName").First();
    var val3 = (string)transactions.Descendants("Set").Elements("szExternalID").First();

    dataToBeWritten.Append(val1);
    dataToBeWritten.Append(",");

    dataToBeWritten.Append(val2);
    dataToBeWritten.Append(",");

    dataToBeWritten.Append(val3);
    dataToBeWritten.Append(",");

    dataToBeWritten.Append(Environment.NewLine);
} // End of For each var trans

Answer 3

如果您愿意使用库（Cinchoo ETL - 一个开源 ETL 库），还有另一种方法可以进行这种类型的转换

基于流，只需几行代码即可快速将任何 xml 转换为 csv 格式。

我相信您想从您的 xml 中生成仅包含 CUSTOMER 表元素的 CSV 文件。

这里是你可以如何使用这个库

using (var parser = new ChoXmlReader("sample.xml").WithXPath("/UpdateDB/Transaction")
    .WithField("Table", xPath: "/Insert/Table")
    .WithField("szCustomerID", xPath: "/Insert/Set/szCustomerID")
    .WithField("szCustomerName", xPath: "/Insert/Set/szCustomerName")
    .WithField("szExternalID", xPath: "/Insert/Set/szExternalID")
    )
{
    using (var writer = new ChoCSVWriter("sample.csv").WithFirstLineHeader())
        writer.Write(parser.Where(r => r.Table == "CUSTOMER").Select(r => new { szCustomerID = r.szCustomerID, szCustomerName = r.szCustomerName, szExternalID = r.szExternalID }));
}

输出如下所示

szCustomerID,szCustomerName,szExternalID
2988880562567,130808125028SHM,3177@06/07/17
12345,130808125028SHM,3177@06/07/17

更新：

为了将 szExternalID 拆分为 2 列（szExternalID、szExternalDate），您必须使用 valueconverter 来解析和加载它们。示例展示了如何

using (var parser = new ChoXmlReader("sample.xml").WithXPath("/UpdateDB/Transaction")
    .WithField("Table", xPath: "/Insert/Table")
    .WithField("szCustomerID", xPath: "/Insert/Set/szCustomerID")
    .WithField("szCustomerName", xPath: "/Insert/Set/szCustomerName")
    .WithField("szExternalID", xPath: "/Insert/Set/szExternalID", valueConverter: (v) => ((string)v).Split('@')[0])
    .WithField("szExternalDate", xPath: "/Insert/Set/szExternalID", valueConverter: (v) => ((string)v).Split('@')[1])
    )
{
    using (var writer = new ChoCSVWriter("sample.csv").WithFirstLineHeader())
        writer.Write(parser.Where(r => r.Table == "CUSTOMER").Select(r => new { szCustomerID = r.szCustomerID, szCustomerName = r.szCustomerName, szExternalID = r.szExternalID, szExternalDate = r.szExternalDate }));
}

新的输出如下所示

szCustomerID,szCustomerName,szExternalID,szExternalDate
2988880562567,130808125028SHM,3177,06/07/17
12345,130808125028SHM,3177,06/07/17

披露：我是这个库的作者。