[TYPO3-50-general] Identity definition - integrity checks?

[Manuel Strausz]

Hey all,
first of all I'm pretty new to FLOW3 and some of the underlying concepts - 
mostly the JSR-283 implementation is kind of hard to grasp for me since I'm 
quite used to working with relational database systems. So please forgive my 
kind of naive question. :)
I just completed the tutorial and everything worked fine, except for the 
last part where you build your own BlogRoutePartHandler. In the end the URLs 
were generated correctly, but I would get an exception when clicking on it 
("Uncaught exception #1237305720. Querying the repository for the specified 
object was not successful..") which basically says that it coul not find the 
blog object associated with the identity. After checking in the TYPO3RC 
backend, I found that the object was indeed existing though - twice.
After some deeper digging through the Mapper class, I found out that the 
Mapper indeed found 2 objects, but returned FALSE since there were 2 found 
with the same identifier key.

So my question is this, is this behaviour on purpose? Should it be possible 
to store 2 objects with the same identity property value, but then getting 0 
results when the system queries for it by calling the 
Mapper::findObjectByIdentityProperties method?

Of course, in the real world I'd have a validator making sure that no 2 
objects with the same identity property get stored. But from a database 
integrity point of view, even if some 'duplicate identity' objects try to 
slip in, shouldn't there be a mechanism to prevent this?

Regards,
Manuel

P.S.: There was an error message added to the mapping results, but this 
doesn't show up in the log. Only the exception did. Any way to make these 
kinds of errors show up? I think this would at least give some kind of hint 
as to why the query failed to return objects.