When can I use Unidirectional relationships in NHibernate?

Question

I'm trying to port a large graph of .NET entities to use NHibernate, but I'm encountering an issue that most of the relationships are only defined unidirectionally - in most cases, the child class contains a reference to the parent, but the parent does not contain the collection of refs to its children. It would be quite a bit of work to add all the collections to turn the relationships into bidirectional ones, so I'm wondering what the consequences for NHibernate would be of not doing so?

One consequence I've noticed is that cascading deletes seem to fail (child doesn't get deleted in the DB, causing a referential integrity violation). Is that the only consequence or are there other issues I need to be aware of?

Are there any guidelines for when relationships should be uni or bi-directional?

Thanks

Answer 1

I think that not being able to cascade the deletes will be the only issue with NHibernate per se.

But you will not be able to easily walk the graph. You can do it from child to parent, but obviously not from parent to child. So you would have to issue a query each time you want all the childs from a parent.

So if you are using NH for a persisted domain model, where you have a root object from which you need to use the child objects for certain operations, you would have to issue queries from within the model to get the children. So your model will be coupled to your data access.

Or you would have to pass the children to the parent object as collections, but then it might be just at easy to have the collections on the model to begin width so NH could fill them for you.