- fixes #36

Author: claytondaley

src/concurrency/config.py

@@ -50,7 +50,9 @@ class AppSettings(object):
         'FIELD_SIGNER': 'concurrency.forms.VersionFieldSigner',
         'POLICY': CONCURRENCY_LIST_EDITABLE_POLICY_SILENT,
         'CALLBACK': 'concurrency.views.callback',
-        'HANDLER409': 'concurrency.views.conflict'}
+        'HANDLER409': 'concurrency.views.conflict',
+        'IGNORE_DEFAULT': True,
+    }
 
     def __init__(self, prefix):
         """

src/concurrency/fields.py

@@ -184,11 +184,23 @@ def _do_update(model_instance, base_qs, using, pk_val, values, update_fields, fo
                     # else:
                     #     new_version = old_version
                     break
-            if values:
+
+            # This provides a default if either (1) no values were provided or (2) we reached this code as part of a
+            # create.  We don't need to worry about a race condition because a competing create should produce an
+            # error anyway.
+            updated = base_qs.filter(pk=pk_val).exists()
+
+            # This second situation can occur because `Model.save_base` calls `Model._save_parent` without relaying
+            # the `force_insert` flag that marks the process as a create.  Eventually, `Model._save_table` will call
+            # this function as-if it were in the middle of an update.  The update is expected to fail because there
+            # is no object to update and the caller will fall back on the create logic instead.  We need to ensure
+            # the update fails (but does not raise an exception) under this circumstance by skipping the concurrency
+            # logic.
+            if values and updated:
                 if (model_instance._concurrencymeta.enabled and
                         conf.ENABLED and
                         not getattr(model_instance, '_concurrency_disabled', False) and
-                        old_version):
+                        (old_version or not conf.IGNORE_DEFAULT)):
                     filter_kwargs = {'pk': pk_val, version_field.attname: old_version}
                     updated = base_qs.filter(**filter_kwargs)._update(values) >= 1
                     if not updated:
@@ -197,8 +209,6 @@ def _do_update(model_instance, base_qs, using, pk_val, values, update_fields, fo
                 else:
                     filter_kwargs = {'pk': pk_val}
                     updated = base_qs.filter(**filter_kwargs)._update(values) >= 1
-            else:
-                updated = base_qs.filter(pk=pk_val).exists()
 
             return updated
 

tests/test_base.py

@@ -1,4 +1,6 @@
 import pytest
+from django.test import override_settings
+
 from demo.util import concurrent_model, unique_id, with_all_models, with_std_models
 
 from concurrency.core import _set_version
@@ -54,6 +56,22 @@ def test_do_not_check_if_no_version(model_class):
     assert instance.get_concurrency_version() != copy.get_concurrency_version()
 
 
+@pytest.mark.django_db(transaction=True)
+@with_std_models
+def test_conflict_no_version_and_no_skip_flag(model_class):
+    """When IGNORE_DEFAULT is disabled, attempting to update a record with a default version number should fail."""
+    with override_settings(CONCURRENCY_IGNORE_DEFAULT=False):
+        id = next(unique_id)
+        instance, __ = model_class.objects.get_or_create(pk=id)
+        instance.save()
+
+        copy = refetch(instance)
+        copy.version = 0
+
+        with pytest.raises(RecordModifiedError):
+            copy.save()
+
+
 @with_std_models
 @pytest.mark.django_db(transaction=False)
 def test_update_fields(model_class):