Fluent NH
Fluent NHibernate offers an alternative to NHibernate’s standard XML
mapping files. Rather than writing XML documents, you write mappings
in strongly typed C# code. This allows for easy refactoring, improved
readability and more concise code.
vs.
NH’s new mapping by code
It is an XML-less mapping solution being an integral part of
NHibernate since 3.2, based on ConfORM library. Its API tries to
conform to XML naming and structure. There’s a strong convention in
how the mapping methods are built. Its names are almost always equal
to XML elements names.