Controlling cascade order

[Pete Appleton]

Firstly, my apologies for the HTML mail with a picture – I hope this doesn’t cause too much offence, but I wasn’t able to articulate the issue without resorting to graphics.

 

The picture below shows a simplified object graph that we’re trying to update in a single transaction.  Our handle onto the graph is a new (transient) instance of entity [C] – everything in the graph is new except for the [QB] entity which is existing.  All collections are marked as cascade style all-delete-orphan, and the one-to-one association from [C] to [A] is marked as a save-update as is the many-to-one from [S] to [QB].  The association from [A] to [C] is not marked with any cascade annotation.

 

When we attempt to persist this graph we get a transient object exception relating to [Q] at the point where NHibernate attempts to persist the new instance(s) of [P] because NHibernate has yet to traverse the [C] -> [A] association; if we omit the [P] -> [Q] link by setting the mapped property to null and temporarily permitting nulls then the DB operation is successful.  Clearly, for this operation to succeed the new [Q] instances must be persisted prior to anything else because the top-level entities depend upon them.  How can we ensure that this happens please?

 

Thanks in advance,

/Pete

 

[Pete Appleton]

In case anyone else has a similar issue, we were able to resolve this with the following actions:

 

1.  Add a save-update cascade from [A] to [C]

2.  Use [QB] as the handle to the object graph instead of the new instance of [C]

 

My belief is that the 'best' way of handling complex cascades would be to order the graph operations by dependency using the cascade and nullability settings to determine the edges, but I haven't noticed any graph algorithms in the NH codebase.  Is this a feature that people think would be worth implementing, or is it too far removed from the current methodology?

 

/Pete

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