On Apr 1, 2008, at 8:17 AM, Dov Rosenberg wrote:
I have been tracking down a strange error in our app.
java.lang.IllegalStateException: There is no database snapshot
available for the object
In a lot of places we use a new EditingContext instead of the
default Editing Context for the session. When we use a new editing
context we have been very careful to lock and unlock before and
after use.
How? What do you use? Where / how do you do this?
In some places we use the session default EditingContext (we are
probably going to stop doing that in the future). A couple of
questions come to mind:
• I have read that it is not necessary to lock the session default
EditingContext because EOF will automanage it. What happens if it
does get manually locked? The error above was thrown when trying to
do an ec.lock() on a Session.defaultEditingContext().
I'd really go a long way to avoid locking and unlocking the default
EC. This can lead to serious problems, especially around session
termination.
• What physically happens when an EC is locked? It seems it is some
sort of reference counter. In an earlier post Chuck mentioned that
locking the EODatabaseContext will prevent fetches/saves from
occurring, what happens when an EC is locked?
Mostly it prevents other threads from updating its state (e.g. when an
EC in those threads saves changes to objects in this EC). The changes
are queued for later processing.
• Is there any compelling reason to use the session default editing
context? We aren’t using Project Wonder (yet)
I use them for things whose lifetime matches the session: logged in
user, their permissions, etc.
Chuck
--
Practical WebObjects - for developers who want to increase their
overall knowledge of WebObjects or who are trying to solve specific
problems.
http://www.global-village.net/products/practical_webobjects
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