- Fixed regression within the flush process when an attribute were

set to a SQL expression for an UPDATE, and the SQL expression when
compared to the previous value of the attribute would produce a SQL
comparison other than ``==`` or ``!=``, the exception "Boolean value
of this clause is not defined" would raise.   The fix ensures that
the unit of work will not interpret the SQL expression in this way.
fixes #3402

3 files changed, 53 insertions, 7 deletions

diff --git a/doc/build/changelog/changelog_10.rst b/doc/build/changelog/changelog_10.rst
index fd791ea97..1e67221f5 100644
--- a/doc/build/changelog/changelog_10.rst
+++ b/doc/build/changelog/changelog_10.rst
@@ -19,6 +19,17 @@
     :version: 1.0.3
 
     .. change::
+        :tags: bug, orm
+        :tickets: 3402
+
+        Fixed regression within the flush process when an attribute were
+        set to a SQL expression for an UPDATE, and the SQL expression when
+        compared to the previous value of the attribute would produce a SQL
+        comparison other than ``==`` or ``!=``, the exception "Boolean value
+        of this clause is not defined" would raise.   The fix ensures that
+        the unit of work will not interpret the SQL expression in this way.
+
+    .. change::
         :tags: bug, ext
         :tickets: 3397
 
diff --git a/lib/sqlalchemy/orm/persistence.py b/lib/sqlalchemy/orm/persistence.py
index 34c37dab6..c3974ed6d 100644
--- a/lib/sqlalchemy/orm/persistence.py
+++ b/lib/sqlalchemy/orm/persistence.py
@@ -452,12 +452,11 @@ def _collect_update_commands(
                 value = state_dict[propkey]
                 col = propkey_to_col[propkey]
 
-                if not state.manager[propkey].impl.is_equal(
+                if isinstance(value, sql.ClauseElement):
+                    value_params[col] = value
+                elif not state.manager[propkey].impl.is_equal(
                         value, state.committed_state[propkey]):
-                    if isinstance(value, sql.ClauseElement):
-                        value_params[col] = value
-                    else:
-                        params[col.key] = value
+                    params[col.key] = value
 
         if update_version_id is not None and \
                 mapper.version_id_col in mapper._cols_by_table[table]:
diff --git a/test/orm/test_unitofwork.py b/test/orm/test_unitofwork.py
index ae5a8ef60..5a47903f0 100644
--- a/test/orm/test_unitofwork.py
+++ b/test/orm/test_unitofwork.py
@@ -7,7 +7,8 @@ from sqlalchemy.orm import mapper as orm_mapper
 
 import sqlalchemy as sa
 from sqlalchemy.util import u, ue, b
-from sqlalchemy import Integer, String, ForeignKey, literal_column, event
+from sqlalchemy import Integer, String, ForeignKey, \
+    literal_column, event, Boolean
 from sqlalchemy.testing import engines
 from sqlalchemy import testing
 from sqlalchemy.testing.schema import Table
@@ -18,6 +19,7 @@ from sqlalchemy.testing import fixtures
 from test.orm import _fixtures
 from sqlalchemy.testing.assertsql import AllOf, CompiledSQL
 
+
 class UnitOfWorkTest(object):
     pass
 
@@ -383,16 +385,26 @@ class ClauseAttributesTest(fixtures.MappedTest):
             Column('name', String(30)),
             Column('counter', Integer, default=1))
 
+        Table('boolean_t', metadata,
+            Column('id', Integer, primary_key=True,
+                   test_needs_autoincrement=True),
+            Column('value', Boolean),
+            )
+
     @classmethod
     def setup_classes(cls):
         class User(cls.Comparable):
             pass
 
+        class HasBoolean(cls.Comparable):
+            pass
+
     @classmethod
     def setup_mappers(cls):
         User, users_t = cls.classes.User, cls.tables.users_t
-
+        HasBoolean, boolean_t = cls.classes.HasBoolean, cls.tables.boolean_t
         mapper(User, users_t)
+        mapper(HasBoolean, boolean_t)
 
     def test_update(self):
         User = self.classes.User
@@ -446,6 +458,30 @@ class ClauseAttributesTest(fixtures.MappedTest):
 
         assert (u.counter == 5) is True
 
+    def test_update_special_comparator(self):
+        HasBoolean = self.classes.HasBoolean
+
+        # make sure the comparison we're shooting
+        # for is invalid, otherwise we need to
+        # test something else here
+        assert_raises_message(
+            TypeError,
+            "Boolean value of this clause is not defined",
+            bool, None == sa.false()
+        )
+        s = create_session()
+        hb = HasBoolean(value=None)
+        s.add(hb)
+        s.flush()
+
+        hb.value = sa.false()
+
+        s.flush()
+
+        # needs to be refreshed
+        assert 'value' not in hb.__dict__
+        eq_(hb.value, False)
+
 
 class PassiveDeletesTest(fixtures.MappedTest):
     __requires__ = ('foreign_keys',)