Apply new uniquing rules for future ORM selects

Fixed issue where usage of the :meth:`_result.Result.unique` method with an
ORM result that included column expressions with unhashable types, such as
``JSON`` or ``ARRAY`` using non-tuples would silently fall back to using
the ``id()`` function, rather than raising an error. This now raises an
error when the :meth:`_result.Result.unique` method is used in a 2.0 style
ORM query. Additionally, hashability is assumed to be True for result
values of unknown type, such as often happens when using SQL functions of
unknown return type; if values are truly not hashable then the ``hash()``
itself will raise.

For legacy ORM queries, since the legacy :class:`_orm.Query` object
uniquifies in all cases, the old rules remain in place, which is to use
``id()`` for result values of unknown type as this legacy uniquing is
mostly for the purpose of uniquing ORM entities and not column values.

Fixes: #6769
Change-Id: I5747f706f1e97c78867b5cf28c73360497273808

1 files changed, 11 insertions, 2 deletions

diff --git a/lib/sqlalchemy/orm/context.py b/lib/sqlalchemy/orm/context.py
index 0af3fd6af..c4b695687 100644
--- a/lib/sqlalchemy/orm/context.py
+++ b/lib/sqlalchemy/orm/context.py
@@ -81,6 +81,7 @@ class QueryContext(object):
         _yield_per = None
         _refresh_state = None
         _lazy_loaded_from = None
+        _legacy_uniquing = False
 
     def __init__(
         self,
@@ -2257,6 +2258,10 @@ class _QueryEntity(object):
 
     __slots__ = ()
 
+    _non_hashable_value = False
+    _null_column_type = False
+    use_id_for_hash = False
+
     @classmethod
     def to_compile_state(cls, compile_state, entities, entities_collection):
 
@@ -2387,6 +2392,7 @@ class _MapperEntity(_QueryEntity):
 
     supports_single_entity = True
 
+    _non_hashable_value = True
     use_id_for_hash = True
 
     @property
@@ -2483,7 +2489,6 @@ class _MapperEntity(_QueryEntity):
 
 
 class _BundleEntity(_QueryEntity):
-    use_id_for_hash = False
 
     _extra_entities = ()
 
@@ -2663,9 +2668,13 @@ class _ColumnEntity(_QueryEntity):
         return self.column.type
 
     @property
-    def use_id_for_hash(self):
+    def _non_hashable_value(self):
         return not self.column.type.hashable
 
+    @property
+    def _null_column_type(self):
+        return self.column.type._isnull
+
     def row_processor(self, context, result):
         compile_state = context.compile_state