Hibernate version: 2/3
with cascade="all"

In general one-to-many mapping situation such as this: "An Order has Many OrderItems"
I have Order and OrderItem classes mapped such that I can do:

orderObject.getOrderItems(); to retrieve all the OrderItems associated with that Order.

and if I wanna add an OrderItem Object to that Order, then I can do:

orderObject.getOrderItems().add( aNewOrderItem );

where aNewOrderItem is a newly instantiated orderItem object.

So, every time I am adding aNewOrderItem object to the set, Hibernate is going to query first and fetch all the objects in the set, then it's going to add the new object to the set.
This works nicely if my Set of OrderItems of orderObject is fairly small.

But what if the Set of orderItems become very large, in such a case wouldn't this operation be rather slow??

Should I rather just use the OrderItemDAO class seperately to add aNewOrderItem? But this approach requires more coding... what is the right approach here?

If the size of the OrderItems table is too large for your DB server to serve up quickly, then yes, you could remove the relationship and do the work in factory code. However, you are labouring under a misconception:

This isn't correct. Hibernate will load items only if you reference them, unless you've specifically told it to eagerly load the items. In your example, Hibernate won't load any members of the OrderItem set if you're just adding a new item. It knows that "insert into OrderItem ..." will work just fine without loading all those other items.

Thanks for the reply. However, I still have some confusion. Because when I executed: orderObject.getOrderItems().add( aNewOrderItem );

with hibernate.show_sql turned on, I saw the query for select query to getOrderItems() as well as for insert. So, from what I understand as long as those collection items are not referenced, they will not be acutally initialized, is this correct?

You can prove to yourself whether or not the set is being fully loaded by turning on parameter logging. In you log4j.parameters, add this line:That will show you all the data that is being loaded from the DB. It is possible that the ids for all the OrderItems are being loaded, but I think that that only happens when you use a query to load the items, as opposed to a colleciton mapping. If you're loading an OrderObject and seeing all its OrderItems being loaded, I'd imagine that you are eagerly fetching the collection.

Actually, now that I think about it a bit more, it is probable that the set would have to be fully loaded in order to add a new item. This is because of the general constract of a set: it cannot contain duplicates. The only way to find out if a set contains an item that you're adding is to load every item in the set and compute its hashCode. Because of this, you may find that you will have to change your mapping to a simple many-to-one association from OrderItem to OrderObject, and use a factory class to query an OrderObject's OrderItems.