Default xml attribute value when using LINQ

Question

Let's say you have an XML file:

<experiment
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:noNamespaceSchemaLocation="experiment.xsd">
  <something />
<experiment>

And you have the xsd file:

...
<xs:attribute name="hello" type="xs:boolean" use="optional" default="false" />
...

Let's assume that the attribute "hello" is an optional attribute of the "something" element with a default value set to "false".

When using XDocument of XML LINQ, the attribute is missing, causing the program to fail while trying to read it:

XDocument xml = XDocument.Load("file.xml");
bool b = bool.Parse(xml.Descendants("something").First().Attribute("hello").Value); // FAIL

Does LINQ load the XML schema automatically (from the "xsi:noNamespaceSchemaLocation" attribute of the root element "experiment") or do I have to force it manually?

How to force LINQ to read the optional attributes and their default values?

Answer 1

The Load method takes an XmlReader, if you use one with the right XmlReaderSettings http://msdn.microsoft.com/en-us/library/1xe0740a (ie requiring validation with ValidationType set to schema and paying attention to schemaLocation respectively noNamespaceSchemaLocation with the proper ValidationFlags) then I think the attribute will be created and populated with the default from the schema.

Here is a short sample:

    XDocument doc;

    XmlReaderSettings xrs = new XmlReaderSettings();
    xrs.ValidationType = ValidationType.Schema;
    xrs.ValidationFlags |= XmlSchemaValidationFlags.ProcessSchemaLocation;


    using (XmlReader xr = XmlReader.Create("../../XMLFile1.xml", xrs))
    {
        doc = XDocument.Load(xr);
    }
    foreach (XElement foo in doc.Root.Elements("foo"))
    {
        Console.WriteLine("bar: {0}", (bool)foo.Attribute("bar"));
    }

With samples file having the contents

<?xml version="1.0" encoding="utf-8" ?>
<root xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="XMLSchema1.xsd">
  <foo/>
  <foo bar="true"/>
  <foo bar="false"/>
</root>

<?xml version="1.0" encoding="utf-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
  <xs:element name="root">
    <xs:complexType>
      <xs:sequence maxOccurs="unbounded">
        <xs:element name="foo">
          <xs:complexType>
            <xs:attribute name="bar" use="optional" type="xs:boolean" default="false"/>
          </xs:complexType>
        </xs:element>
      </xs:sequence>
    </xs:complexType>
  </xs:element>
</xs:schema>

the output is

bar: False
bar: True
bar: False

Answer 2

Using this Xml Library XElementExtensions.cs class you can use the Get() method that takes a default value:

XDocument xml = XDocument.Load("file.xml");
bool b = xml.Descendants("something").First().Get("hello", false); 

false is the default you provide.