Bug: None has no attribute parent

[jamoore]

None returned from experimenter.copyGroupExperimenterMap() when the data in the DB looks like this:

 select * from groupexperimentermap where child = 5;
id | permissions | owner | version | child | external_id | parent | child_index 
----+-------------+-------+---------+-------+-------------+--------+-------------
12 |        -103 | f     |       0 |     5 |             |      1 |           1
(1 row)

i.e. when there's a null in the list of groups.

Request Method: GET
Request URL: http://localhost:8080/webadmin/experimenters/
Django Version: 1.3.1
Exception Type: AttributeError
Exception Value:

'NoneType' object has no attribute 'parent'

Exception Location: /private/tmp/sprint7/dist/lib/python/omero/gateway/__init__.py in isActive, line 3967

[wmoore]

I can easily add a check for None when iterating through the links, but not sure why you'd get a None from that query?

        for ob in self._obj.copyGroupExperimenterMap():
            if ob.parent.name.val == "user":
                return True

[jmoore]

That collection is ordered. If for whatever reason there's a gap in the ordering, Hibernate will convert that to a None in the list. In theory, though, that shouldn't be happening and we should figure out how the null got there.

[jmoore]

Passing to Will for a final decision.

[wmoore]

This commit should fix the Bug above ​https://github.com/will-moore/openmicroscopy/commit/988559feb14136947a325c3f74dda0ee453fbe65

but if we generally can't be sure that retrieving an ordered collection won't have items that are None, then there are a ton of places where we'd need to add that similar checks. Seems to me that it would be a lot nicer if the server could filter out any None values from results before returning to clients.

[jmoore]

Sorry, Will. Impossible. The nulls are part of the contract. An ordered collection can by definition have blanks in it. There's no way to strip them out without having the ordering destroyed in the DB. (Imagine a missing well from a plate. It would shift position)

[wmoore]

This bug is fixed by the commit above. Fixing this problem in general is a new ticket: #9140. Closing...