What is Castle proxy factory in NHibernate?

Question

What is Castle proxy factory in NHibernate? What is its task? What does proxy mean in this case?

Answer 1

Castle can be used (amongst others, you have the choice, you can also use LinFu, Spring.NET, ...) to create dynamic proxies of your entities.

By default, NHibernate uses dynamic proxies to represent your entities; by doing so, it is able to return an object to you when you retrieve some entity from the DB, without all properties being populated. By using a dynamic proxy, it will only populate the entity once you really refer to a property.
(So it is some kind of lazy loading; not to be confused with lazy loading of collections / associations though).

This behaviour is the reason why NHibernate wants you to create every property as virtual by default: NHibernate will create a new class using this Castle (or LinFu, ...) proxy provider which inherits from your entity, and it will override all the properties so that it can 'inject' the code that is necessary to retrieve the necessary data from the DB.

You can disable this behaviour by specifying 'lazy=false' in your entity mapping. (Although, I do think that even if you disable this feature, NHibernate will still require that you use one of the proxy factories).

Answer 2

When you are selecting an entity from ISession you are getting not real entity instance - you are getting proxy object. This proxy object inherits your entity and used by NHibernate to track changes made to the fields.

Answer 3

see it: http://en.wikipedia.org/wiki/Proxy_pattern