Thanks a lot for very quick reply Andrus! =)
Hmm.... I tried your suggestion but notice the follow things:
1. Cayenne relies on DataContext.hasChanges() to know whether there is
any real modifications. But this only allows Cayenne to know whether
there are any modifications within the DataContext, not based on
individual DataObjects.
2. Due to the above, once there is a single modified DataObject within
the DataContext, the validate* methods will be called for all
DataObjects marked modified.
As such, I think your suggestion does not work.
I'm not sure how useful will it be to the rest of the users, but I guess
having the PersistenceState.MODIFIED to reflect real modifications are
intuitive and useful in most cases. Or perhaps we can have an option to
turn it On/Off....
On the same line, perhaps out-of-the-box Cayenne could support the use
of fields like TimeStamp, as it would help alot in users who are
re-engineering from existing DB systems which relies on this feature.
-- SeanAndrus Adamchik wrote:
> Hi there, > > Your solution will work and you can put your overridden > "writeProperty" in your own custom superclass of DataObjects thus > changing default Cayenne behavior. > > Here is another solution however - override "validateForSave" to add > your timestamp logic: > > http://objectstyle.org/cayenne/userguide/dataobjects/validation.html > > See, even if an object is marked as modified on "setXYZ" call when > there was no real modification, this fact will be detected by Cayenne > later on commit, and the object will not be committed, and its > validate* methods won't be called. > > Hope this helps. > > Andrus > > On Aug 26, 2005, at 2:03 PM, Sean Tan wrote: > >> I'm attempting to use Cayenne v1.1.2 with the idea of having a field >> that mimics the behavior of MySql's TimeStamp dbtype. >> >> The timestamp will only update if at least a change is detected in the >> rest of the columns. >> >> I'm trying to rely on the PersistenceState of CayenneDataObject but I >> realized that the PersistenceState is set to Modified even when the new >> value being introduced is the same as the old value. This poses a >> problem, especially in the context of webframeworks like Tapestry which >> all bounded fields will be updated, meaning the writeProperty(String >> propName, Object val) of the CayenneDataObject will always be >> called.... >> PersistenceState being set to Modified although no change is made. >> >> One usage scenario is when you create a HTML table of records which >> allows the user to change the records inline, and click on a update >> button. >> >> Thus, I'm proposing that perhaps the writeProperty method could be >> adjusted to do additional check as below to suit this purpose. >> ---- >> public void writeProperty(String propName, Object val) { >> resolveFault(); >> >> // 1. retain object snapshot to allow clean changes tracking >> // 2. change object state >> Object oldVal = readPropertyDirectly(propName); >> if (persistenceState == PersistenceState.COMMITTED && >> oldVal.equals(val) == false) { >> persistenceState = PersistenceState.MODIFIED; >> dataContext.getObjectStore().retainSnapshot(this); >> } >> // else.... >> // other persistence states can't be changed to MODIFIED >> >> writePropertyDirectly(propName, val); >> } >> ----- >> >> Or am I missing out a better way to do this? >> >> -- >> Sean Tan > > >
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