Hi could someone help explain this.

In hibernate what is the difference between List and Bag? When is it preferable to use one over the other, and which is the one to go for? At the moment I use the bag element, but in my Java code I'm using the ArrayList collection class.

search the wiki,
bags are usefull when you add an element to an uninitialised big collection, it avoids the collection to be loaded.
All this is related to Set and List contracts

also check bidirectionnal specs

Java actually has a Bag, but its called Collection.

[quote="anthony"]search the wiki,
bags are usefull when you add an element to an uninitialised big collection, it avoids the collection to be loaded.
All this is related to Set and List contracts

also check bidirectionnal specs[/quote]

thanks. i guess i was just looking for as to which one i should be using most of the time. If a List offers more benefits than a Bag, then obviously I'll use a list but I'm just curious as to which scenarios.

I guess when you only get objects insert,bag is a little better than set or map,otherwise you shouldn't use bag in other cases else.Bacause bag will clear all objects contained by itself and reload all objects when it get objects delete or insert.

Please read the documentation, there are many hints when to use what collection.

When using a list element, I noticed that my index column in my BlogItem table "indexCol" doesn't get populated with the index of the element in the list, it still remains as null.

This is my mapping file containing the list part.
<list name="items" inverse="true" lazy="true" cascade="all">
<key column="BlogIDFK"/>
<index column="indexCol"/>
<one-to-many class="eg.BlogItem"/>
</list>

However when I take away the inverse=true part of the list tag, the index of the object in the list is written to the indexCol column. Can someone explain why it happens like that?
<list name="items" lazy="true" cascade="all">
<key column="BlogIDFK"/>
<index column="indexCol"/>
<one-to-many class="eg.BlogItem"/>
</list>

Thanks for the link. The information there solved the problem. However I'm just wondering which approach is more correct since they both do the same thing and produce the same result (setting inverse to false, or setting inverse to true and handling the index of the collection manually by having an index property in your class). Why set inverse to true when you have to manually handle the index?

It would appear that it is not possible then to have a
list with inverse="true" for a many-to-many relationship.