C＃验证xml

Question

I have 2 xsd schemas:

A.xsd

<?xml version="1.0" encoding="utf-8"?>
<xs:schema elementFormDefault="qualified" xmlns:xs="http://www.w3.org/2001/XMLSchema" targetNamespace="myns" xmlns:myns="myns">
  <xs:include schemaLocation="B.xsd"/>
  <xs:element name="A">
    <xs:complexType>
      <xs:sequence>
        <xs:element ref="myns:B" />
      </xs:sequence>
    </xs:complexType>
  </xs:element>
</xs:schema>

and B.xsd

<?xml version="1.0" encoding="utf-8"?>
<xs:schema elementFormDefault="qualified" xmlns:xs="http://www.w3.org/2001/XMLSchema" targetNamespace="myns">
  <xs:element name="B" type="xs:string" />
</xs:schema>

And I have 2 xml file:

first

<?xml version='1.0' encoding='utf-8' ?>
<A xmlns='myns'>
  <B xmlns='myns'>sdf</B>
</A>

second

<?xml version='1.0' encoding='utf-8' ?>
<B xmlns='myns'>sdf</B>

I validate xml with this code

var schemas = new XmlSchemaSet();
schemas.Add("myns", "A.xsd");
xdoc.Validate(schemas, OnValidating);

Both of these xml is valid, but I need that first xml is valid and second not. How can I do this?

XSD schemas supplied by a third parties and can not be changed.

Answer 1

The problem you have cannot be solved using your stock validator only. The fact that XSD components are spread across different files means nothing to the XSD validator. The idea is that a "Reference to schema components from a schema document is managed in a uniform way, whether the component corresponds to an element information item from the same schema document or is imported" .

So, without application specific constraints, a document having a root element A vs. another one with a root element B, would validate the same, simply because the processor can find a global element declaration for both.

What you need to do is create a custom "pre-validation" step based on some configuration information defining the list of allowed root elements. If the document element's qualified name is found in the list, then proceed with the normal validation; otherwise, fail it right from the beginning. Probing for the document element's name in a way that doesn't add runtime overhead to your application depends on how your XML is acquired, ie if DOM is involved, or if the readers and/or the underlying stream can seek, etc.

Regarding the list of allowed elements... if it happens that any of the global elements found in A.xsd is considered by your application as a valid document element in an XML instance document, then you can easily extract the list of allowed root elements qualified names by traversing A.xsd file using .NET's SOM API ; iterate through the XmlSchema.Items looking for XmlSchemaElement types and its QualifiedName property.

You could use a dictionary to cache the list of allowed qualified names, or LINQ through the collection, etc.