Rename ConcurrentUpdate to ConcurrentTransition

ConcurrentUpdate is too generic - one might get a feeling that
it catches all concurrent updates (like optimistic lock does),
when in fact it only catches concurrent state transitions.

django_fsm/__init__.py

@@ -12,7 +12,7 @@
 from django_fsm.signals import pre_transition, post_transition
 
 
-__all__ = ['TransitionNotAllowed', 'ConcurrentUpdate',
+__all__ = ['TransitionNotAllowed', 'ConcurrentTransition',
            'FSMFieldMixin', 'FSMField', 'FSMIntegerField',
            'FSMKeyField', 'FSMLockMixin', 'transition',
            'can_proceed', 'has_transition_perm']
@@ -33,7 +33,7 @@ class TransitionNotAllowed(Exception):
     """Raised when a transition is not allowed"""
 
 
-class ConcurrentUpdate(Exception):
+class ConcurrentTransition(Exception):
     """
     Raised when the transition cannot be executed because the
     object has become stale (state has been changed since it
@@ -350,7 +350,7 @@ class FSMLockMixin(object):
 
     Instance of a model based on this Mixin will be prevented from saving into DB if any
     of its state fields (instances of FSMFieldMixin) has been changed since the object
-    was fetched from the database. *ConcurrentUpdate* exception will be raised in such
+    was fetched from the database. *ConcurrentTransition* exception will be raised in such
     cases.
 
     For guaranteed protection against such race conditions, make sure:
@@ -399,7 +399,7 @@ def _do_update(self, base_qs, using, pk_val, values, update_fields, forced_updat
         # Thus, we need to make sure we only catch the case when the object *is* in the DB, but with changed state; and
         # mimic standard _do_update behavior otherwise. Django will pick it up and execute _do_insert.
         if not updated and base_qs.filter(pk=pk_val).exists():
-            raise ConcurrentUpdate("Cannot save object! The state has been changed since fetched from the database!")
+            raise ConcurrentTransition("Cannot save object! The state has been changed since fetched from the database!")
 
         return updated
 

tests/testapp/tests/test_lock_mixin.py

@@ -1,6 +1,6 @@
 from django.db import models
 from django.test import TestCase
-from django_fsm import FSMField, FSMLockMixin, ConcurrentUpdate, transition
+from django_fsm import FSMField, FSMLockMixin, ConcurrentTransition, transition
 
 
 class LockedBlogPost(FSMLockMixin, models.Model):
@@ -65,7 +65,7 @@ def test_concurent_modifications_raise_exception(self):
 
         post2.text = 'aaa'
         post2.publish()
-        with self.assertRaises(ConcurrentUpdate):
+        with self.assertRaises(ConcurrentTransition):
             post2.save()
 
     def test_inheritance_crud_succeed(self):