Hi,

I've got a set of child entities that don't have any primary key, just a foreign key to a parent (e.g. there's no way of determining an individual child, they can only be treated as a collection). I only ever seem to get one child entity in the ISet. If I add a primary key (e.g. change the id tag to a surrogate id) I get the expected result. The SQL being executed looks correct, but I'm assuming it's something to do with Child equality? Any help appreciated.

Code below has been edited for brevity.


and mapping files:

The identifier for your child objects are the parents identifer, two objects related to the same parent will have the same identifier and therefore be identical when compared by nHibernate.

So adding two transient children to your parent(and save them) will fail because an object with that identifier is already in the session.

I must admit i fail to see what you are trying to accomplish.

A second thing is that you are using a "set" and from what i see you want to allow duplicates.

Thanks for the response, your explanation makes sense.

I'm trying to model an unordered set of children that refer to a parent object but don't in themselves have any identifier - an id column here makes no sense, as individually the children are of no interest. Is overriding Equals enough here? The objects should only be considered equal if all the fields are equal (the fields were omitted in the example), not if ParentId is equal.

The behaviour I want is that if changes are made to the collection the whole thing is deleted and re-saved (i.e. DELETE FROM children WHERE parent_id = ? ; INSERT ... ). Maybe this isn't something hibernate does; our model requires this in a number of places for good or for ill.

Thanks,

Steve

This is what i would call a value-type, in nHibernate this is done using components as described in the reference manual chapter 7

You can easily make it work like you describe by mapping your parent class like this(the Child class is now a "component" instead of a class this way it has no life of its own in nHibernates eyes)



I added name as an example for your components properties, it can of course have multiple properties.

Hope this helps

Hi,

That appears to work for loading, thanks for the help. NHibernate doesn't seem to be saving the collection now though... the mapping file is pretty much as you suggested. Any ideas?

How does the code look where you add/remove from the collection?

Sorry, it looks like this..



Even if I change an existing child I don't get any UPDATES in the SQL Hibernate's producing - it's like it's decided not to track changes at all. As an aside, I haven't overriden Equals and GetHashCode (although doing so didn't appear to have any effect on this). Again, thanks for your help on this.

Steve

Remove inverse="true" from your <set> tag in the mapping

That was stupid of me - thanks again for the help. Just out of interest, I notice in the SQL that NHibernate runs separate DELETE and INSERTs for each element of the collection - is there a way to amalgamate these operations (since the entire collection's keyed off the parent id)?

Thanks again for your help, appreciate it.

Steve

The only reason i can think of for deleting the children one by one is that you don't wan't to delete children that could have been added since you retrieved the collection

Yes, true. Although I would've thought that the responsibility for that would be down to using locking (as it would be with entity updates where the data could've changed underneath you). It doesn't matter for small collections but for larger ones it gets inefficient.