- merge of ticket_3514 None-handling branch

- Fixes to the ORM and to the postgresql JSON type regarding the
``None`` constant in conjunction with the Postgresql :class:`.JSON` type.  When
the :paramref:`.JSON.none_as_null` flag is left at its default
value of ``False``, the ORM will now correctly insert the Json
"'null'" string into the column whenever the value on the ORM
object is set to the value ``None`` or when the value ``None``
is used with :meth:`.Session.bulk_insert_mappings`,
**including** if the column has a default or server default on it.  This
makes use of a new type-level flag "evaluates_none" which is implemented
by the JSON type based on the none_as_null flag. fixes #3514
- Added a new constant :attr:`.postgresql.JSON.NULL`, indicating
that the JSON NULL value should be used for a value
regardless of other settings. part of fixes #3514

1 files changed, 13 insertions, 0 deletions

diff --git a/lib/sqlalchemy/sql/type_api.py b/lib/sqlalchemy/sql/type_api.py
index 8f502ac02..701e2a44a 100644
--- a/lib/sqlalchemy/sql/type_api.py
+++ b/lib/sqlalchemy/sql/type_api.py
@@ -129,6 +129,19 @@ class TypeEngine(Visitable):
 
     """
 
+    evaluates_none = False
+    """If True, the Python constant ``None`` is considered to be handled
+    explicitly by this type.
+
+    The ORM will use this flag to ensure that a positive value of ``None``
+    is definitely passed to the backend, ignoring whether or not there
+    are Python or server side defaults on this column.
+
+    .. versionadded:: 1.1
+
+
+    """
+
     def compare_against_backend(self, dialect, conn_type):
         """Compare this type against the given backend type.