Infrastructure

• .NET 1.1 is no longer supported
• Nullables.NHibernate is no longer supported (use nullable types of .NET 2.0)
• Contrib projects moved to http://sourceforge.net/projects/nhcontrib

Compile time

• NHibernate.Expression namespace was renamed to NHibernate.Criterion
• IInterceptor have additional methods. (IsUnsaved was renamed IsTransient)
• INamingStrategy
• IType
• IEntityPersister
• IVersionType
• IBatcher
• IUserCollectionType
• IEnhancedUserType
• IPropertyAccessor
• ValueTypeType renamed to PrimitiveType 

Possible Breaking Changes for external frameworks

• Various classes were moved between namespaces
• Various classes have been renamed (to match Hibernate 3.2 names)
• ISession interface have additional methods
• ICacheProvider
• ICriterion
• CriteriaQueryTranslator

Initialization time

• <nhibernate> section, in App.config, is no longer supported and will be ignored. Configuration schema for configuration file and App.config is now identical, and the App.config section name is:
• <hibernate-configuration> have a different schema and all properties names are cheked
• configuration properties are no longer prefixed by “hibernate.”, if before you would specify “hibernate.dialect”, now you specify just “dialect”
• All named queries will be validated at initialization time, an exception will be thrown if any is not valid (can be disabled if needed)
• Stricter checks for proxying classes (all public methods must be virtual)

Run time

• SaveOrUpdateCopy() returns a new instance of the entity without changing the original
• AutoFlush will not occur outside a transaction - Database transactions are never optional, all communication with the database must occur inside a transaction, whatever you read or write data.
• NHibernate will return long for count(*) queries on SQL Server
• <formula> must contain parenthesis when needed
• The HQL functions names may cause conflic in your HQL (reserved names are: substring, locate, trim, length, bit_length, coalesce, nullif, abs, mod, sqrt, upper, lower, cast, extract, concat, current_timestamp, sysdate, second, minute, hour, day, month, year, str)
• <any> when meta-type=”class” the persistent type is a string containing the Class.FullName (In order to set a parameter in a query you must use SetParameter(“paraName”, typeof(YourClass).FullName, NHibernateUtil.ClassMetaType) )

Mapping

• <any> : default meta-type is “string” (was “class”)