c＃LINQ从XElement获取属性值

Question

I have the below XML in a data definitions file:

<PQTemplate documentID="CSTrlsEN" documentType="TransList" templateID="001" 
        templateType="Customer Copy" 
        templateName="C:\CPS\_templates\Mini-Statements\CSTrlsEN.doc">  
<field pos="5" name="YPTME" descr="Time"  />
<field pos="6" name="YPDTE" descr="Action Date"  />
<field pos="7" name="YPBRNO" descr="Branch Number"  />
<field pos="8" name="YPBNA" descr="Branch Name"  />
<field pos="9" name="YPTID" descr="Teller ID"  />
<field pos="10" name="YPISN" descr="Teller Sequence"  />
<field pos="11" name="YPREF" descr="Customer Reference"  />
<field pos="12" name="YPCUS" descr="Customer Name"  />
<field pos="13" name="YPEAN" descr="Account Number"  />
<field pos="14" name="YPATY" descr="Account Type"  />
<field pos="15" name="YPCUR" descr="Currency"  />
<field pos="16" name="YPBAL" descr="Available Balance"  />

I get that specific XElement using LINQ, extracting it from an XML file that contains several PQTemplate elements by using the below LINQ Expression:

var mapInfo = from nm in XElement.Elements("PQTemplate")
                where (string)nm.Attribute("documentID") == sRequests[0].Split('\t')[0] 
                select nm;    

Now I need to get the value of the attribute documentType so I tried the below LINQ Expression:

var repName = from d in mapInfo.Attributes("documentType")
                     select d.Value;

reportName = repName.ToString();

Unfortunately although I can see the value TransList is part of the reportName element, I have had no luck trying to retrieve it.

Here is an image showing it in VS 2013:

so how can I get the documentType attribute in the element?

Answer 1

That's because repName will return an IEnumerable<string> for all the mapInfo .

IEnumerable<string> repName = from d in mapInfo.Attributes("documentType")
                     select d.Value;

So either use a foreach loop if you suspect you may get more values or use First to get first attribute like this:-

string reportName = mapInfo.First().Attribute("documentType").Value;

Answer 2

Linq queries return collections. Do for each over repName or

repName.First().ToString()

if that is all you need.

Answer 3

Your solution depends on how many elements DocumentType exist in your XML. If it´s only one (what I suppose) you may use repName.First().ToString() .

If the attribute may occure more than once you should use a loop instead:

var result = new List<string>();
foreach(var a in (from d in mapInfo.Attributes("documentType") select d.Value) 
    result.Add(a.ToString());

Or even shorter:

result = mapInfo.Attributes("documentType").Select(x => x.Value.ToString());

Which will return an enumeration.

Answer 4

Change

var mapInfo = from nm in XElement.Elements("PQTemplate")
                where (string)nm.Attribute("documentID") == sRequests[0].Split('\t')[0] 
                select nm;   

to

var mapInfo = from nm in XElement.Elements("PQTemplate")
                where (string)nm.Attribute("documentID") == sRequests[0].Split('\t')[0] 
                select nm.Attribute("documentType").Value;   

then mapInfo.First() will give you the value you want.

Answer 5

To get a single value out of a LINQ query you have to call for example First or FirstOrDefault . If you call FirstOrDefault it won't throw an exception if the query returns no matches.

string repName =  doc.Elements("PQTemplate")
                     .Where(e => (string)a.Attribute("documentID") == sRequests[0].Split('\t')[0])
                     .Select(e => (string)e.Attribute("documentType"))
                     .FirstOrDefault();

Also, you don't need to call ToString() on XAttribute.Value as it's already a string .