Is there a way to define reusable properties to n-hibernate mappings?

Question

I have a scenario that i want to add some standard properties to my entities. Meaning that i will have e.g. 1 int and 2 string properties applied to all relevant entities. I have over 100 mapping files and most but not all will be hosts to these new properties. In the classes its easy to define this; in the mappings however i've found no reference other than creating a utility or xslt and applying that (How to define reusable <generator> elements in hibernate mapping).

However i want to be able to add/modify/remove properties from this "standard" mapping.

thx for any replies

Edit1: an example of the mapping i want to add

<property name="TimeOfEdit" column="TimeOfEdit" type="DateTime" not-null="true"/>
<many-to-one name="EditedBy" column="FK_EditedBy" cascade="save-update" not-null="true" />

Edit2: I removed the accepted solution because with NH 2.1.1 XML Entities are not working (NH-1236) and NH will throw a "DTD is prohibited in this XML document"

Answer 1

It seems that the only to do this, is to use Dynamic Mapping (http://ayende.com/Blog/archive/2008/05/01/Dynamic-Mapping-with-NHibernate.aspx)

as such since i've already defined an interface that my entities will use for the new properties (lets say IAuditable) its just a matter of running the appropriate code at the NH-session initialization

Configuration cfg = new Configuration() Mappings mappings = cfg.CreateMappings(); 
foreach (var persistentClass in mappings.Classes) 
{ 
   if (persistentClass.MappedClass is IAuditable)
   {
     ...
   }
}

and then

cfg.BuildSessionFactory();

to have it wired up and ready to be used for about 85 classes the performance impact is negligible

Answer 2

It depends on how these properties are implemented in your classes.

If they are all defined in a base class or interface, you could map them once in the base class or interface, and derive using union-subclass. There are some limitations. Read this chapter in the NHibernate documentation about it.

If you decide to put them together into a class, you could map them as a user type. This will be similar to a component, but you could specify some things like type names, lengths and others in the user type. You still need to specify each column name.

There is another option: you could use XML entities. This is a rather primitive feature from XML which is supported by NHibernate. Read this chapter in the NH reference documentation where it is mentioned.

Answer 3

Creating a special code generator for your specific case is your only option.

Answer 4

Option 1:
-Define these 3 properties in a base class

-have your entities inherit from this base

-set up 'table per class hierarchy'

Option 2:

-Define these 3 properties as a component.

-You can have the mapping for these 3 properties in one file that is reused.

Answer 5

You might take a look at fluentNHibernate, It will simplify the mapping work for you. With With auto mapping you may only need an abstract base class to define these properties.