When adding a Python constraint on a (relational) field which uses an
other (relational) field, the order in which the fields are written is
also the order in which they are checked, and if a constraint depends
on a sibling field this might blow up in P3, here as in as in
test_new_api.message.Message (_check_author constraint depends on
parent discussion's participants): test_11_stored would commonly fail
when creating a discussion with two participants and 3
messages (because the message's authors would be checked before the
participants had been associated with the discussion).
Xavier Morel
ea21c7a8ee