Linq to XML动态XML后代

Question

I'm parsing a lot of XML files using Linq to XML synatx, everything works when I try to access top level elements

var indexroot = (from element in prodcutDocument.Root.Descendants("indexroot")
                        select new
                        {
                            model = (string)element.Element("MODEL"),
                        }).FirstOrDefault()

The problem occurs when I need to access lower level childs of that document I tried:

var indexroot = (from element in prodcutDocument.Root.Descendants("indexroot")
                        select new
                        {
                            ddName = (string)element.Descendants("DD_NAME").Elements("name").First();
                            }).FirstOrDefault()

and

var indexroot = (from element in prodcutDocument.Root.Descendants("indexroot").Descendants("DD_NAME")
                             select new
                             {
                                 ddName = (string)element.Element("name")
                             }).FirstOrDefault();

Sadly none of that works and i get same error "Sequence contains no elements". And one more thing sometimes the XML document contains those tags and sometimes not is something like this enough for handling this case?

var indexroot = (from element in prodcutDocument.Root.Descendants("indexroot").Descendants("DD_NAME")
                             select new
                             {
                                 ddName = (string)element.Element("name") ?? "-"
                             }).FirstOrDefault();

Edit: I don't think is possible to paste short version of XML that would be simple, so here's full version: http://pastebin.com/uDkP3rnR and for the code example:

XDocument prodcutDocument = XDocument.Load(this.ServerPATHData + file); 

var indexroot = (from element in prodcutDocument.Root.Descendants("indexroot")
            select new
            {
                modelis = (string)element.Element("MODELIS"),
                T2918_0 = (string)element.Descendants("dd_DARBINIS_GRAFIKAS_SPEC").First()
            }).FirstOrDefault();

writeTxt.WriteLine("modelis: " + indexroot.modelis);
writeTxt.WriteLine("T2979_0" + indexroot.T2918_0); 

Answer 1

You can just change:

element.Descendants("dd_DARBINIS_GRAFIKAS_SPEC").First()

to this:

element.Descendants("dd_DARBINIS_GRAFIKAS_SPEC").FirstOrDefault() ?? "-"

Answer 2

In examining the sample XML that you posted on PasteBin, it appears to me that the elements that you mention appear only once. To access them, you can simply specify a path to each as follows:

XElement indexroot = document.Root.Element("indexroot");
XElement modelis = indexroot.Element("MODELIS");
XElement dd_dgs = indexroot.Element("dd_DARBINIS_GRAFIKAS_SPEC");

XElement voltageuv = dd_dgs.Element("VoltageUV");

string t2979_0 = (string)voltageuv.Element("T2979_0");
string t2861_60 = (string)voltageuv.Element("T2861_60");
string t2757_121 = (string)voltageuv.Element("T2757_121");

(Note that you may need to check for null if there is a chance that any of the elements you are trying to access may not be present. Without doing so, you'll encounter a NullReferenceException .)

Here is a snippet of the XML that you posted to give context to the above code:

<?xml version='1.0' encoding='UTF-8' standalone='no'?>
<PDB>
  <indexroot>
    <ed_BENDRA_MAKS_SUV_GALIA>1.45</ed_BENDRA_MAKS_SUV_GALIA>
    <ed_BENDRA_MAKS_SROVE>6.48</ed_BENDRA_MAKS_SROVE>
    <TIPAS>1</TIPAS>
    <MODELIS>RIS 2500 HW EC 3.0</MODELIS>
    <dd_DARBINIS_GRAFIKAS_SPEC>
      <VoltageUV>
        <T2979_0>229,42</T2979_0>
        <T2861_60>227,98</T2861_60>
        <T2757_121>228,97</T2757_121>
      </VoltageUV>
      <CurrentIA>
        <T2979_0>2,56</T2979_0>
        <T2861_60>2,63</T2861_60>
        <T2757_121>2,72</T2757_121>
      </CurrentIA>
    </dd_DARBINIS_GRAFIKAS_SPEC>
  </indexroot>
</PDB>