In the world of NHibernate usually usage of Sets are encouraged. But bags have one advantage. When you add an Item to a bag, it does not load all the items from db. In the case of set it will load entire set in order to add your new item.

Yes I know we can only initiate the non-inverse side but that doesn't seem a pleasant solution. Instead why not use bags ?

Considering there might be too many items in the bag in future, I feel relying on bags by default rather than sets is a safer bet. What do you think ?

I would be surprised if that were true.

I would have thought that the purpose of a Set is to ensure that all items in the collection for the current session are unique, before persisting.

http://www.hibernate.org/hib_docs/nhibe ... ialization

As you see from docs this is true!

Hi emperon,

What text in that doco makes you think that all existing rows in the database are loaded, if a collection is mapped as a Set?

Yes, sets need to initialize themselves if you want to add an item since they must return true/false depending on whether the add succeded.

PandaWood, It is in 15.5.3.

So why not using bags by default ? Why nhibernate community promotes sets instead of bags despite of this ? What other disadvantages bag s have over sets ?

One possible disadvantage of bags, is that you can't eager-fetch two collections of bags at the same time.