Viridium.ro

If you worked with NHibernate mappings, you know very well about the namespace declarations on the root element: <hibernate-mapping xmlns="urn:nhibernate-mapping-2.2">. We generate these mappings programmatically, and we naturally wondered how to remove the default xmlns:xsd and xmlns:xsi declarations that the XmlSerializer adds, and add the NHibernate URN in the mix. The recipe below outlines the three necessary steps.

Step 1

Suppress the xmlns:xsi andxmlns:xsd declarations that XmlSerializer creates by default.

var namespaces = new XmlSerializerNamespaces();
namespaces.Add(string.Empty, string.Empty);
var serializer = new XmlSerializer(typeof(T));
serializer.Serialize(t, writer, namespaces);

We now have a clean root element, free of any namespace declarations.

Step 2

Add the NHibernate namespace declaration. An overloaded constructor of XmlSerializer does the trick:

var namespaces = new XmlSerializerNamespaces();
namespaces.Add(string.Empty, string.Empty);
var serializer = new XmlSerializer(typeof(T), "urn:nhibernate-mapping-2.2");
serializer.Serialize(t, writer, namespaces);

We now get the namespace declaration, but with a namespace prefix. Besides, since that prefix is not then used on the elements inside the root, the resulting document is not correct. What we want is a default namespace declaration. (See XML Namespaces for a roadmap.)

Step 3

Remove the namespace prefix from the declaration (make it a default namespace declaration.)

var namespaces = new XmlSerializerNamespaces();
namespaces.Add(string.Empty, "urn:nhibernate-mapping-2.2");
var serializer = new XmlSerializer(typeof(T), "urn:nhibernate-mapping-2.2");
serializer.Serialize(t, writer, namespaces);

The document is now consistent with the goal. A default namespace declaration associates the root element and all its child nodes with the desired URI.

What happens if you skip some of these steps? Some things will go wrong:

• If you don’t use the overloaded constructor in step 2, you get no namespace declarations on the hibernate-mapping element.
• If you use the overloaded constructor, but not the namespaces collection in step 1, the NHibernate URN gets an XmlSerializer-assigned namespace alias. I got xmlns:q1=urn:nhibernate-mapping-2.2".
• And finally, if you don’t include the NHibernate URN with an empty alias, as I did in step 3, you get no namespace declarations on the hibernate-mapping element.