Propose Result as immediate replacement for ResultProxy

As progress is made on the _future.Result, including breaking
it out such that DBAPI behaviors are local to specific
implementations, it becomes apparent that the Result object
is a functional superset of ResultProxy and that basic
operations like fetchone(), fetchall(), and fetchmany()
behave pretty much exactly the same way on the new object.
Reorganize things so that ResultProxy is now referred to
as LegacyCursorResult, which subclasses CursorResult
that represents the DBAPI-cursor version of Result,
making use of a multiple inheritance pattern so that
the functionality of Result is also available in non-DBAPI
contexts, as will be necessary for some ORM
patterns.

Additionally propose the composition system for Result
that will form the basis for ORM-alternative result
systems such as horizontal sharding and dogpile cache.
As ORM results will soon be coming directly from
instances of Result, these extensions will instead
build their own ResultFetchStrategies that perform
the special steps to create composed or cached
result sets.

Also considering at the moment not emitting deprecation
warnings for fetchXYZ() methods; the immediate issue
is Keystone tests are calling upon it, but as the
implementations here are proving to be not in any
kind of conflict with how Result works, there's
not too much issue leaving them around and deprecating
at some later point.

References: #5087
References: #4395
Fixes: #4959
Change-Id: I8091919d45421e3f53029b8660427f844fee0228

4 files changed, 7 insertions, 12 deletions

diff --git a/lib/sqlalchemy/orm/exc.py b/lib/sqlalchemy/orm/exc.py
index b04b844b3..7b0f84866 100644
--- a/lib/sqlalchemy/orm/exc.py
+++ b/lib/sqlalchemy/orm/exc.py
@@ -8,6 +8,8 @@
 """SQLAlchemy ORM exceptions."""
 from .. import exc as sa_exc
 from .. import util
+from ..exc import MultipleResultsFound  # noqa
+from ..exc import NoResultFound  # noqa
 
 
 NO_STATE = (AttributeError, KeyError)
@@ -146,14 +148,6 @@ class UnmappedColumnError(sa_exc.InvalidRequestError):
     """Mapping operation was requested on an unknown column."""
 
 
-class NoResultFound(sa_exc.InvalidRequestError):
-    """A database result was required but none was found."""
-
-
-class MultipleResultsFound(sa_exc.InvalidRequestError):
-    """A single database result was required but more than one were found."""
-
-
 class LoaderStrategyException(sa_exc.InvalidRequestError):
     """A loader strategy for an attribute does not exist."""
 
diff --git a/lib/sqlalchemy/orm/loading.py b/lib/sqlalchemy/orm/loading.py
index 5ef2f10ec..d781df980 100644
--- a/lib/sqlalchemy/orm/loading.py
+++ b/lib/sqlalchemy/orm/loading.py
@@ -141,7 +141,7 @@ def merge_result(query, iterator, load=True):
             result = []
             keys = [ent._label_name for ent in query._entities]
             keyed_tuple = result_tuple(
-                keys, [ent.entities for ent in query._entities]
+                keys, [tuple(ent.entities) for ent in query._entities]
             )
             for row in iterator:
                 newrow = list(row)
@@ -528,7 +528,7 @@ def _instance_processor(
 
         if adapter:
             pk_cols = [adapter.columns[c] for c in pk_cols]
-        tuple_getter = result._tuple_getter(pk_cols, True)
+        tuple_getter = result._tuple_getter(pk_cols)
 
     if mapper.allow_partial_pks:
         is_not_primary_key = _none_set.issuperset
diff --git a/lib/sqlalchemy/orm/mapper.py b/lib/sqlalchemy/orm/mapper.py
index 31f005769..c05705b67 100644
--- a/lib/sqlalchemy/orm/mapper.py
+++ b/lib/sqlalchemy/orm/mapper.py
@@ -2647,8 +2647,9 @@ class Mapper(sql_base.HasCacheKey, InspectionAttr):
         pk_cols = self.primary_key
         if adapter:
             pk_cols = [adapter.columns[c] for c in pk_cols]
+        rk = result.keys()
         for col in pk_cols:
-            if not result._has_key(col):
+            if col not in rk:
                 return False
         else:
             return True
diff --git a/lib/sqlalchemy/orm/query.py b/lib/sqlalchemy/orm/query.py
index ab49a4dcc..6ec520a3e 100644
--- a/lib/sqlalchemy/orm/query.py
+++ b/lib/sqlalchemy/orm/query.py
@@ -4315,7 +4315,7 @@ class _MapperEntity(_QueryEntity):
             polymorphic_discriminator=self._polymorphic_discriminator,
         )
 
-        return _instance, self._label_name, self.entities
+        return _instance, self._label_name, tuple(self.entities)
 
     def setup_context(self, query, context):
         adapter = self._get_entity_clauses(query, context)