I have ~20 classes mapped in NHibernate
absolutely all classes are lazy = false, and at runtime
it makes millions of selects and very very slow
i've read Hibernate In Action and many documentation but
i couldn't find the best solution.

can somebody help?

i can't make anything lazy because i use all the data in the objects
to 'hydrate' other objects (business objects). of course,
i could make everything lazy but then i'd have to modify alot of
code to enable session connection/disconnection from
the client application, which is a very bad solution

all i want is to retrieve all association tree in the best time
without performing thousands of selects

thanks for help!

Use explicit queries and join the associated objects you want using SetFetchMode/Join (ICritiera/IQuery). Don't join too much tough, espacially if you have multiple collections on one entity (=cartesian product).

I'd suggest you try to use lazy loading. As said - if needed, create explicit queries matching your specific use case to ensure you have appropiate data when traversing your graphs.

there isn't any way that i can optimally retrieve an object and
all the assosiacions?

Lets say we have
class Cat
{
public string Name {get;set;}
public List<Cat> Kittens {get;set;}
public List<Cat> Pals {get;set;}
}

If i'd want to retrieve all of the associations of a cat:
from Cat cat join fetch cat.Kittens, join fetch cat.Pals

This HQL generetes a single select if i'm not mistakeing.
But why do you say it makes a cartesian product?
That's inneficient.

Yes - it can be inefficient. That's what I wrote :)
It's really just how outer joins work. In your case the number of rows in the set would be [number of cats]*[number of kittens]*[numbers of pals].

If it performs too slow, you'll better see if it's more efficient to run two or more queries in your case instead.

In most circumstances lazy loading makes sense, that's why in 1.2 it was changed to the default.

If your objects are going to passed through some type of boundary then I suggest using coarser grained objects. You can find an example here: http://elegantcode.com/2007/11/06/dtos-presentation-model-and-icriteria/ (I prefer ICriteria to IQuery). A single SQL statement will be used to populate the DTO.

It makes a cartesian product because it will return a row for every combination of Kitten and Pal.

For this case a MultiQuery can be used: see the end of this section: http://www.hibernate.org/hib_docs/nhibe ... ulti-query

Multiquery is efficient when retrieving all association for one object.
But when i want all objects and for each all collections?
I think there isn't any efficient way of obtaining this.

it's like i'd want to do something like this in SQL:

SELECT cat.* , ( SELECT * from Kittens WHERE cat_id = cat.Id ) ,
( SELECT * from Pals WHERE cat_id = cat.Id )
FROM Cats cat
which is imposiible i think

MultiQuery is an alternative. Fill up the session cache and then (implicitly) query that rather than the db. However as I indicated above I would use DTOs here.

i am using DTO's... i don't understand what you mean by DTO's though:
lightweight objects called Data Transfer Objects?

By DTOs I mean a targeted view of the Domain. The Domain is a more generalized model. DTOs have a more specialized purpose e.g. to populate a specific screen.

Note however that this thread suggests that NHibernate's use of proxies might require references to NHibenate on the remote side (which if it is true is not ideal): http://forum.hibernate.org/viewtopic.php?t=983775