The change token can only be used to detect changes within an object.
The problem here is that we are potentially dealing with two objects.
The root of the problem is that a path is not a stable key for an object.
An object can be updated in the repository without our knowledge. The
cache would then return an outdated object and everybody should be
prepared for that. refresh() reloads the current state from the
repository. That works fine if the object is retrieved through
getObject(). You can move the object around, unfile it, put it in
multiple folders and it still works. The object id is unambiguous.
The cache currently maps object paths to object ids. When you call
getObjectByPath() it will look up the id for this path and gets the
object from the cache. If you move the object to a different folder,
getObjectByPath() shouldn't find it anymore. The path of the object has
changed and the old path is now invalid. Note that the object hasn't
changed and therefore the change token hasn't either.
Since there is no notification from the repository, the path-to-id
mapping can't be corrected. The cache still thinks the object is
accessible through this path. So getObjectByPath() returns the object
although it should throw a CmisObjectNotFound exception.
Let's assume we create a new object in the place where the old object
was. The new object can now be accessed with the old path. Since the
outdated path-to-id mapping is still in place, getObjectByPath() returns
the old object and not the new one -- which clearly wrong.
The problem that we are facing here is that there is no reliable way to
keep the path-to-id mapping up-to-date. If we want to be correct, we
would have to ask the repository for the current id for the given path
every time getObjectByPath() is called (3) -- or not use the cache at
all (2).
- Florian
On 16/11/2010 08:23, Jens Hübel wrote:
Shouldn't the change token solve that? How do we deal with the change token for
other objects that are in the local cache? Ignore? Check on each access?
Configurable?
Jens
-----Original Message-----
From: Florian Müller [mailto:[email protected]]
Sent: Montag, 15. November 2010 21:17
To: [email protected]
Subject: getObjectByPath cache problem
Hi all,
I had another look at [1]. Unfortunately, it's an unsolvable problem.
I can think of three ways to cope with it:
1. We leave it like it is, although it is very, very confusing when you run
into this situation.
2. We don't cache by path. How would that affect applications?
3. When getObjectByPath is called we fetch the object id from the repository
and then get the object from the cache.
In the worst case, we would have to hit the repository twice.
Any opinions?
- Florian
[1] https://issues.apache.org/jira/browse/CMIS-260
