- 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

2 files changed, 18 insertions, 2 deletions

diff --git a/lib/sqlalchemy/orm/mapper.py b/lib/sqlalchemy/orm/mapper.py
index 48fbaae32..3efaa45ac 100644
--- a/lib/sqlalchemy/orm/mapper.py
+++ b/lib/sqlalchemy/orm/mapper.py
@@ -1915,6 +1915,19 @@ class Mapper(InspectionAttr):
     """
 
     @_memoized_configured_property
+    def _insert_cols_evaluating_none(self):
+        return dict(
+            (
+                table,
+                frozenset(
+                    col.key for col in columns
+                    if col.type.evaluates_none
+                )
+            )
+            for table, columns in self._cols_by_table.items()
+        )
+
+    @_memoized_configured_property
     def _insert_cols_as_none(self):
         return dict(
             (
@@ -1922,7 +1935,8 @@ class Mapper(InspectionAttr):
                 frozenset(
                     col.key for col in columns
                     if not col.primary_key and
-                    not col.server_default and not col.default)
+                    not col.server_default and not col.default
+                    and not col.type.evaluates_none)
             )
             for table, columns in self._cols_by_table.items()
         )
diff --git a/lib/sqlalchemy/orm/persistence.py b/lib/sqlalchemy/orm/persistence.py
index 0bfee2ece..c785a4dee 100644
--- a/lib/sqlalchemy/orm/persistence.py
+++ b/lib/sqlalchemy/orm/persistence.py
@@ -375,10 +375,12 @@ def _collect_insert_commands(
 
         propkey_to_col = mapper._propkey_to_col[table]
 
+        eval_none = mapper._insert_cols_evaluating_none[table]
+
         for propkey in set(propkey_to_col).intersection(state_dict):
             value = state_dict[propkey]
             col = propkey_to_col[propkey]
-            if value is None:
+            if value is None and propkey not in eval_none:
                 continue
             elif not bulk and isinstance(value, sql.ClauseElement):
                 value_params[col.key] = value