How do I write a Lambda statement for this Linq to XML function?

Question

I am working with this XSD file. The portion of the XML that is relevant to this question is here:

<?xml version="1.0"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
           xmlns="https://wsmrc2vger.wsmr.army.mil/rcc/manuals/106-11" 
           targetNamespace="https://wsmrc2vger.wsmr.army.mil/rcc/manuals/106-11"
           elementFormDefault="qualified" 
           attributeFormDefault="unqualified">
    <xs:element name="Tmats">
        <xs:complexType>
            <xs:sequence>
                <xs:annotation>
                    <xs:documentation>TMATS G Group</xs:documentation>
                </xs:annotation>
                <xs:element name="ProgramName" type="xs:string" minOccurs="0">
                    <xs:annotation>
                        <xs:documentation>PN</xs:documentation>
                    </xs:annotation>
                </xs:element>

To get the documentation value for a given xs:element, I have this small function, which recursively walks the descendant nodes until it finds the documentation element:

public string GetCode(XElement e)
{
    foreach (var s in e.Elements())
    {
        // If we hit an intervening element, bail out.
        if (s.Name.ToString().Contains("element"))
            return "";

        if (s.Name.ToString().Contains("annotation"))
        {
            // I'll explain this loop in a moment.
            foreach (var t in s.Elements())
            {
                if (t.Name.ToString().Contains("documentation"))
                    return t.Value;
            }
        } 
        else
            return GetCode(s);
    }
    return "";
}

So far so good. The unit test looks like this:

[TestMethod()]
public void GetCodeTest()
{
    string path = @"C:\Documents and Settings\harvey robert\Desktop\Tmats.xsd";

    IEnumerable<XElement> elements =
        from e in XElement.Load(path).Elements()
        select e;

    TmatsDictionary target = new TmatsDictionary(); 
    XElement x = elements.First();
    string actual = target.GetCode(x);
    Assert.AreEqual("TMATS G Group", actual);
}

Which passes. Now I want to extend the test by adding an additional case, like this:

    XElement z = elements.DescendantsAndSelf()
                         .First(y => y.Attribute("name")
                         .ToString().Contains("ProgramName"));

    actual = target.GetCode(z);
    Assert.AreEqual("PN", actual);

...But this fails due to a null object reference (most likely y.Attribute("name")).

Did you see the loop in the function above that I commented?

// I'll explain this loop in a moment.
foreach (var t in s.Elements())
{
    if (t.Name.ToString().Contains("documentation"))
        return t.Value;
}

It's written that way because I can't figure out how to express the condition in a Lambda statement that works.

Any suggestions?

Robert Harvey · Accepted Answer · 2010-10-26 03:10:15Z

1

You need to use namespaces:

XNamespace ns = "https://wsmrc2vger.wsmr.army.mil/rcc/manuals/106-11";
XElement z = elements.DescendantsAndSelf()
                     .First(y => y.Attribute(ns + "name")
                         .Value.Contains("ProgramName"));

edited Oct 26, 2010 at 3:10

Robert Harvey

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answered Oct 26, 2010 at 2:50

SLaks

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4 Comments

Robert Harvey Over a year ago

Tried that, still getting the same error. Actually, it turns out that an older version of the XSD didn't have the namespaces in it, so I don't think it is the namespaces, but thanks for pointing that out. The IDE says that it is failing on .First(y => y.Attribute(ns + "name")

SLaks Over a year ago

@Robert: What's in y.Attributes()? What are their names?

Robert Harvey Over a year ago

y.Attributes() is a bit hard to isolate. However, elements.DescendantsAndSelf() returns all elements (not just the xs:element elements), and most of the non-xs:element elements don't have attributes, which must explain the null reference error. I suspect I need to do something like elements.DescendantsAndSelf("xs:element").Attribute("name") ..etc, but if I try that, I get the error, "The character : cannot be included in a name." Grf.

SLaks Over a year ago

@Robert: You need to declare an XNamespace for http://www.w3.org/2001/XMLSchema, like I did.

TalentTuner · Accepted Answer · 2010-10-26 03:31:49Z

1

Try this

elements.DescendantsAndSelf().
                First(y => y.Attribute(XName.Get("name", "http://www.w3.org/2001/XMLSchema")));

answered Oct 26, 2010 at 3:31

TalentTuner

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1 Comment

Robert Harvey Over a year ago

That looks like it will work. Is there a way to get it to globally "XNamespace" in the style that SLaks posted, and still get it to recognize the prefix? Your way is a lot of typing if I have to do this in many places.

Gabe · Accepted Answer · 2010-10-26 03:52:49Z

1

Your problem is that y.Attribute("name").ToString().Contains("ProgramName") will fail on every element that doesn't contain a "name" attribute. You need something like this:

y.Attribute("name") != null &&
y.Attribute("name").ToString().Contains("ProgramName");

If you expect all <element> elements to contain a name attribute, you can ignore the null check and do this:

XElement z = elements.DescendantsAndSelf(
                         "{http://www.w3.org/2001/XMLSchema}element")
                     .First(y => y.Attribute("name") 
                     .ToString().Contains("ProgramName"));

EDIT: Note that I added the expanded name to include the namespace URL. See if that works.

edited Oct 26, 2010 at 3:52

answered Oct 26, 2010 at 3:36

Gabe

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3 Comments

Robert Harvey Over a year ago

That's true, but I'd rather just filter out everything but the xs:element elements (which all have attributes) but to do that, I need to figure out how to assign an xs prefix to the thing.

Robert Harvey Over a year ago

Saw your edit. DescendantsAndSelf("element") will only work if I figure out how to use an xs prefix with it. DescendantsAndSelf("xs:element") will not work.

Robert Harvey Over a year ago

Thanks, Gabe. You were right about the expanded name. I figured out how to get that name from the XNamespace, and I posted the working code here.

Robert Harvey · Accepted Answer · 2010-10-26 04:26:48Z

0

Here is the code that works.

Notice the call to the GetName() method in the DescendantsAndSelf() call. This returns a properly formatted URI-prefixed name of the form {http://www.w3.org/2001/XMLSchema}element, which will match correctly to the xs:element names.

The result is that DescendantsAndSelf() returns only those elements having the name xs:element, all of which have attributes associated with them (so there is no chance of a null reference error when referencing the Attributes collection).

[TestMethod()]
public void GetCodeTest()
{
    string path = @"C:\TestArea\Tmats_09-2010.xml";

    IEnumerable<XElement> elements =
        from e in XElement.Load(path).Elements()
        select e;

    TmatsDictionary target = new TmatsDictionary();            
    XNamespace ns = "http://www.w3.org/2001/XMLSchema";

    XElement z = elements.DescendantsAndSelf(ns.GetName("element")) 
                         .First(y => y.Attribute("name")
                         .Value.Equals("ProgramName"));

    actual = target.GetCode(z);
    Assert.AreEqual("PN", actual);
}

edited Oct 26, 2010 at 4:26

answered Oct 26, 2010 at 4:20

Robert Harvey

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3 Comments

Gabe Over a year ago

ns + "element" should work as well as ns.GetName("element")

Robert Harvey Over a year ago

@Gabe: Possibly, but it doesn't look right without a ToString() call, and that makes it too long. I'll try it tomorrow. Anyway, the GetName() call seems to make more sense to me, even though it takes up a few more characters.

Gabe Over a year ago

I didn't think that ns + "element" would even work with a call to ToString(), although I suppose it should.

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