Check for __clause_element__() in ORM insert/update

ORM attributes can now be assigned any object that is has a
``__clause_element__()`` attribute, which will result in inline
SQL the way any :class:`.ClauseElement` class does.  This covers other
mapped attributes not otherwise transformed by further expression
constructs.

As part of this, it was considered that we could add
__clause_element__() to ClauseElement, however this causes endless loops
in a "while" pattern and this pattern has been identified in third
party libraries.  Add a test to ensure we never make that change.

Change-Id: I9e15b3f1c4883fd3909acbf7dc81d034c6e3ce1d
Fixes: #3802

1 files changed, 10 insertions, 0 deletions

diff --git a/test/sql/test_inspect.py b/test/sql/test_inspect.py
index d5a9a71ae..12d377e51 100644
--- a/test/sql/test_inspect.py
+++ b/test/sql/test_inspect.py
@@ -32,3 +32,13 @@ class TestCoreInspection(fixtures.TestBase):
         is_(inspect(c), c)
         assert not c.is_selectable
         assert not hasattr(c, 'selectable')
+
+    def test_no_clause_element_on_clauseelement(self):
+        # re [ticket:3802], there are in the wild examples
+        # of looping over __clause_element__, therefore the
+        # absense of __clause_element__ as a test for "this is the clause
+        # element" must be maintained
+
+        x = Column('foo', Integer)
+        assert not hasattr(x, '__clause_element__')
+