I'm trying to figure out how I can generate a component mapping that relates to a class I have which can be used in multiple entities without having to re-define it in the mapping file for each entity - that'd quickly become irritating if a change was made to the component.

Note that I don't want the class to be an entity, just a component.

I've had a hunt on the hibernate forums and the suggestion was to use an XML external entity using &entity; placeholders, but I've got no idea what that means. Searching google didn't really answer it for me either.

Can anyone explain how the above works - specifically in relation to reusing component mappings in multiple class mappings?

Cheers,

Symon.

read a good XML tutorial. Basically it means that your XML will act like a template, on load the XML parser will replace &entity; constructs with their values which can be defined externally

HTH,
radu

There are could be problems with using external entities if the mapping file is embedded as a resource. It's not known for sure, what XmlResolover NH uses then loads documents from the assembly.

On the other hand you can make your own, quite simple solution:
1. Extend mapping with your custom elements (preferably in your custom namespace).
2. Make a XSLT, which will replace your element(s) with desired constructs.
3. Enumerate resources manually, load necessary one (ending with hbm.xml), transform with your stylesheet and add to the configuration.

Or use NHibernate.Mapping.Attributes (with its [ComponentProperty]) ;)