How can I select only some child nodes from an XML file in C#?

Question

I have an XML file that I want to parse. It is longer than what I shall post here, but only this part interests me in this question:

       <Team>
        <TeamId>1187457</TeamId>
        <TeamName>Zanardi Redwings</TeamName>
        <Arena>
          <ArenaId>1184019</ArenaId>
          <ArenaName>Evolution</ArenaName>
        </Arena>
        <League>
          <LeagueId>37</LeagueId>
          <LeagueName>România</LeagueName>
        </League>
        <Country>
          <CountryId>36</CountryId>
          <CountryName>România</CountryName>
        </Country>
        <LeagueLevelUnit>
          <LeagueLevelUnitId>4109</LeagueLevelUnitId>
          <LeagueLevelUnitName>V.171</LeagueLevelUnitName>
        </LeagueLevelUnit>
        <Region>
          <RegionId>799</RegionId>
          <RegionName>Prahova</RegionName>
        </Region>
        <YouthTeam>
          <YouthTeamId>2337461</YouthTeamId>
          <YouthTeamName>Little Redwings</YouthTeamName>
          <YouthLeague>
            <YouthLeagueId>436902</YouthLeagueId>
            <YouthLeagueName>Normandie Ligue des jeunes</YouthLeagueName>
          </YouthLeague>
        </YouthTeam>
      </Team>

From the part above, I only need to read the data from the TeamId and TeamName child nodes. To achieve this, I wrote the following code:

Nodes = Node.SelectNodes("Team");
foreach (XmlNode j in Nodes)
  {
    XmlNodeList TeamDetails = j.SelectNodes("*");
    foreach (XmlNode k in TeamDetails)
      {
         switch (k.Name)
           {
             case "TeamName":
               {
                  UserTeamNames[counter] = k.InnerXml;
                  break;
               }
             case "TeamId":
               {
                  if (!int.TryParse(k.InnerXml, out UserTeamIDs[counter]))
                   {
                      ShowErrorMessageBox("Parsing TeamID from XML file failed!"); //A function which sets some parameters for MessageBox.Show() then calls it
                   }
                  break;
                }
            }
       }
   }

In the code above, counter is an int variable, which I need in other part of the code.

The code works perfectly, but I want to eliminate the useless looping and testing when the node I am working on is not either TeamName or TeamID .

I suspect the answer I am looking for has something to do with XPath expressions, but I am not sure.

How can I read the data from only the mentioned nodes, without any useless operations?

Answer 1

You can use XmlDocument.GetElementsByTagName method. For your example I will do something like this :

XmlNodeList elemList = doc.GetElementsByTagName("TeamName");
XmlNodeList elemList = doc.GetElementsByTagName("TeamId");

The result is An XmlNodeList containing a list of all matching nodes. If no nodes match name, the returned collection will be empty.

Answer 2

严格按照xpath而言，以下表达式应选择您的节点：

/Team/*[self::TeamId or self::TeamName]

Answer 3

You can filter the xml document using linq then work with your filtered data.

using System;
using System.Linq;
using System.Xml.Linq;
using System.IO;
using System.Xml;

static void Main(string[] args)
{
    var document = new XDocument();

    // use path to your xml file
    using (FileStream fs = File.OpenRead("examp.xml"))
    {
        using (XmlTextReader reader = new XmlTextReader(fs))
        {
            document = XDocument.Load(reader);
        }
    }

    int value;
    var query = (from element in document.Element("Base").Elements("Team")
                 where int.TryParse(element.Element("TeamId").Value.ToString(), out value)
                 select new
                 {
                     TeamName = element.Element("TeamName").Value,
                     TeamId = element.Element("TeamId").Value
                 }).ToList();

    // do further processing with filtered data
    foreach (var item in query)
    {
        Console.WriteLine($"{item.TeamName}: {item.TeamId}");
    }

    Console.ReadKey();
}

Answer 4

Here is another option using LINQ to XML.First create your own class that will hold that data you are looking for like this:

public class TeamInfo
{
    public string TeamName { get; set; }
    public int TeamId { get; set; }
}

Then you would parse the xml into a list of objects like this:

var data =
            "<Team><TeamId>1187457</TeamId><TeamName>Zanardi Redwings</TeamName><Arena><ArenaId>1184019</ArenaId><ArenaName>Evolution</ArenaName></Arena><League><LeagueId>37</LeagueId><LeagueName>România</LeagueName></League><Country><CountryId>36</CountryId><CountryName>România</CountryName></Country><LeagueLevelUnit><LeagueLevelUnitId>4109</LeagueLevelUnitId><LeagueLevelUnitName>V.171</LeagueLevelUnitName></LeagueLevelUnit><Region><RegionId>799</RegionId><RegionName>Prahova</RegionName></Region><YouthTeam><YouthTeamId>2337461</YouthTeamId><YouthTeamName>Little Redwings</YouthTeamName><YouthLeague><YouthLeagueId>436902</YouthLeagueId><YouthLeagueName>Normandie Ligue des jeunes</YouthLeagueName></YouthLeague></YouthTeam></Team>";
        var elm = new XElement("Base",data);
        var decoded = System.Web.HttpUtility.HtmlDecode(elm.ToString());//this is to remove any formatting issues when we call .ToString()

        var doc = XDocument.Parse(decoded);

        var result = doc.Root.Descendants("Team")
            .Select(y => new TeamInfo
            {
                TeamId = Convert.ToInt32(y.Element("TeamId").Value),
                TeamName = y.Element("TeamName").Value
            }).ToList();

    }