Resolving XML Schema documents on-the-fly?

[Lee Chapman]

Has anyone successfully been able to use an XmlValidatingRe ader (Framework
1.1) to validate documents against XML Schemas that haven't been added to
the XmlValidatingRe ader.Schemas collection first?

e.g. I have the following XML document, and I want to validate it.

<doc xmlns="my-first-namspace">
<node/>
<another xmlns="my-second-namespace"/>
</doc>

So I create an XmlValidatingRe ader and instruct it to use a custom
XmlResolver.

XmlTextReader tr = new XmlTextReader(f ullyQualifiedPa th);
XmlValidatingRe ader vr = new XmlValidatingRe ader(tr);
vr.ValidationTy pe = ValidationType. Schema;
vr.XmlResolver = new MyXmlResolver() ;
vr.ValidationEv entHandler += new ValidationEvent Handler(Validat ionEvent);

I then try to load the document, which causes it to be validated.

XPathDocument doc = new XPathDocument(v r);

At this point, my MyXmlResolver.R esolveUri() is called with
fullyQualifiedP ath as the relativeUri parameter, and the System.Uri I return
is then passed to MyXmlResolver.G etEntity(). So far so good.

But the next thing that happens is my ValidationEvent () method gets called
with an XmlSeverityType .Warning message: "Could not find schema information
for the element 'my-first-namespace:doc'. [...]".

I was expecting MyXmlResolver to be used to locate an XML Schema for
my-first-namespace.

If I modify my instance document to provide a schema location hint...

<doc xmlns="my-first-namspace" xsi:schemaLocat ion="my-first-namespace
mfns.xsd">
<node/>
<another xmlns="my-second-namespace"/>
</doc>

....the MyXmlResolver is called to resolve mfns.xsd.

But I can't rely on the instance document having an xsi:schemaLocat ion hint,
so is there any other way I can get XmlValidatingRe ader to ask me where to
get an XML Schema from when it comes across a new namespace?

I can't add the schema to the XmlValidatingRe ader.Schemas collection because
I don't know which schemas the instance document needs to be validated
against until the instance document is loaded. (I guess I could load the
document twice, once with validation and once without, but I was hoping to
achieve everything in one hit, as it were.)

Thanks,
- Lee

[Oleg Tkachenko]

Lee Chapman wrote:

I was expecting MyXmlResolver to be used to locate an XML Schema for
my-first-namespace.
Xmlresolver is supposed to resolve resources by URI, not by namespace,
so no URI - no call to resolver.
But I can't rely on the instance document having an xsi:schemaLocat ion hint,
so is there any other way I can get XmlValidatingRe ader to ask me where to
get an XML Schema from when it comes across a new namespace? Correct me if I'm wrong, but I believe there is no way of doing so. Also
XmlSchemaCollec tion class is sealed, so you cannoty extend it with such
behaviour.
I can't add the schema to the XmlValidatingRe ader.Schemas collection because
I don't know which schemas the instance document needs to be validated
against until the instance document is loaded. (I guess I could load the
document twice, once with validation and once without, but I was hoping to
achieve everything in one hit, as it were.)

Well, if you can try to peek into XML document before validating using
XmlTextReader (just open document and read till doument element, figure
out namespace and then close reader).
--
Oleg Tkachenko
XML Insider
http://www.tkachenko.com/blog