Problems with NHibernate FlushMode Never

Question

We're building a large application with NHibernate as ORM layer. We've tried to apply as many best practices as possible, among which setting FlushMode to Never . However, this is giving us pain, for example the following scenario:

There is a table with an end date column. From this table, we delete the last (by end date) record:

• The record is deleted;
• After the delete, we do a (repository) query for the last record (by end date);
• This last record is updated because it's the new active record.

This is a very simple scenario, of which many exist. The problem here is that when we do the query, we get the deleted record back, which of course is not correct. This roughly means that we cannot do queries in business logic that may touch the entity being inserted or deleted, because its resp. not there yet or still there.

How can I work with this scenario? Are there ways to work around this without reverting the FlushMode setting or should I just give up on the FlushMode setting all together?

Answer 1

How can I work with this scenario? Are there ways to work around this without reverting the FlushMode setting

FlushMode.Never does not prevent you from manually calling Flush() when you want to deal with up-to-date data. I guess it is the way to work this scenario without changing the FlushMode

or should I just give up on the FlushMode setting all together?

Could you provide some reference on FlushMode.Never being a good practice in the general case ? Seems like FlushMode.Never is fit when dealing with large, mostly readonly, sets of objects.

http://jroller.com/tfenne/entry/hibernate_understand_flushmode_never

Answer 2

FlushMode.Never is a best practice only when you absolutely require fine-grained control. FlushMode.Auto will cover 99.99% of the cases without a problem. That said, decorating you CUD operations with a ISession.FLush() will not hurt as it only involves a database roundtrip if there are any CUD actions in the internal action queue

Answer 3

Flush mode Never means NHibernate will never flush the session, it's up to you to do that. So, session.Delete() will not actually delete the record from database, just mark the object for delete in session's cache. You can force a flush by calling session.Flush() after calling session.Delete() .

I think Auto is a better option, with Auto , NHibernate will flush the session automatically before querying for data.