Concurrent-update-check using a hash

dford · **Joined:** Wed Sep 03, 2003 10:40 am **Posts:** 6

Can hibernate perform a concurrent-update-check (stale object check) without version field, but instead using a hash? For example:

Step 1: Load an object from db
Step 2: disconnected (perform a hash of the object's original data)
Step 3: user makes some changes to the object
Step 4: reconnect
Step 5: session.update (re-read object from database and compare with hash)

If the db data's hash doesn't match the object's before-edit hash, then throw a StaleObjectStateException.

steve · **Posted:** Wed Sep 03, 2003 11:06 am

You can acheive this using the "application version checking". Check out the docs on this at http://www.hibernate.org/hib_docs/reference/html/transactions.html#transactions-s3-3

gavin · **Posted:** Wed Sep 03, 2003 8:39 pm

I am implementing more options along these kinds of lines in Hibernate 2.1.

One thing that Hibernate 2.1 can *already* do is perform a check against the current database state when update() is called. This eliminates the requirement for "application version checking" in some cases. (But not in yours.)

We will also soon support optimistic locking on dirty-fields or all-fields.

dford · **Joined:** Wed Sep 03, 2003 10:40 am **Posts:** 6

One more note as a point of interest. I believe this model - concurrent-update (stomp) checking without a version field - is the default model in ADO.NET.

steve · **Posted:** Fri Sep 05, 2003 3:19 pm

FYI, we ran into huge problems with this in Castor against Oracle. The issue has to do with String and VARCHAR columns, and is particularly problematic in web environments. The issue is caused by the fact that Oracle replaces and empty varchar values it finds on INSERT/UPDATE to be null; however, it does not do the same thing during querying.

So consider a Person object with a title field which is not required. Setting the title field on a new person instance to an empty string and then persisting that instance would leave the state as title="" in the java entity, but title=null in the DB.

Later, that person is loaded and the name is updated and person persisted again. The concurrent update check fails because "" is not equal to null according to Oracle (even though they thought it was during the persist).

This is an issue up through 8i. God, I hope they fixed that in 9i.

Just something to consider...