Convert execution to move through Session

This patch replaces the ORM execution flow with a
single pathway through Session.execute() for all queries,
including Core and ORM.

Currently included is full support for ORM Query,
Query.from_statement(), select(), as well as the
baked query and horizontal shard systems.  Initial
changes have also been made to the dogpile caching
example, which like baked query makes use of a
new ORM-specific execution hook that replaces the
use of both QueryEvents.before_compile() as well
as Query._execute_and_instances() as the central
ORM interception hooks.

select() and Query() constructs alike can be passed to
Session.execute() where they will return ORM
results in a Results object.   This API is currently
used internally by Query.   Full support for
Session.execute()->results to behave in a fully
2.0 fashion will be in later changesets.

bulk update/delete with ORM support will also
be delivered via the update() and delete()
constructs, however these have not yet been adapted
to the new system and may follow in a subsequent
update.

Performance is also beginning to lag as of this
commit and some previous ones.   It is hoped that
a few central functions such as the coercions
functions can be rewritten in C to re-gain
performance.  Additionally, query caching
is now available and some subsequent patches
will attempt to cache more of the per-execution
work from the ORM layer, e.g. column getters
and adapters.

This patch also contains initial "turn on" of the
caching system enginewide via the query_cache_size
parameter to create_engine(). Still defaulting at
zero for "no caching".   The caching system still
needs adjustments in order to gain adequate performance.

Change-Id: I047a7ebb26aa85dc01f6789fac2bff561dcd555d

1 files changed, 17 insertions, 13 deletions

diff --git a/lib/sqlalchemy/sql/annotation.py b/lib/sqlalchemy/sql/annotation.py
index 71d05f38f..08ed121d3 100644
--- a/lib/sqlalchemy/sql/annotation.py
+++ b/lib/sqlalchemy/sql/annotation.py
@@ -17,8 +17,12 @@ from .traversals import anon_map
 from .visitors import InternalTraversal
 from .. import util
 
+EMPTY_ANNOTATIONS = util.immutabledict()
+
 
 class SupportsAnnotations(object):
+    _annotations = EMPTY_ANNOTATIONS
+
     @util.memoized_property
     def _annotations_cache_key(self):
         anon_map_ = anon_map()
@@ -40,7 +44,6 @@ class SupportsAnnotations(object):
 
 
 class SupportsCloneAnnotations(SupportsAnnotations):
-    _annotations = util.immutabledict()
 
     _clone_annotations_traverse_internals = [
         ("_annotations", InternalTraversal.dp_annotations_key)
@@ -113,12 +116,9 @@ class SupportsWrappingAnnotations(SupportsAnnotations):
 
         """
         if clone:
-            # clone is used when we are also copying
-            # the expression for a deep deannotation
-            return self._clone()
+            s = self._clone()
+            return s
         else:
-            # if no clone, since we have no annotations we return
-            # self
             return self
 
 
@@ -163,12 +163,11 @@ class Annotated(object):
         self.__dict__.pop("_annotations_cache_key", None)
         self.__dict__.pop("_generate_cache_key", None)
         self.__element = element
-        self._annotations = values
+        self._annotations = util.immutabledict(values)
         self._hash = hash(element)
 
     def _annotate(self, values):
-        _values = self._annotations.copy()
-        _values.update(values)
+        _values = self._annotations.union(values)
         return self._with_annotations(_values)
 
     def _with_annotations(self, values):
@@ -183,10 +182,15 @@ class Annotated(object):
         if values is None:
             return self.__element
         else:
-            _values = self._annotations.copy()
-            for v in values:
-                _values.pop(v, None)
-            return self._with_annotations(_values)
+            return self._with_annotations(
+                util.immutabledict(
+                    {
+                        key: value
+                        for key, value in self._annotations.items()
+                        if key not in values
+                    }
+                )
+            )
 
     def _compiler_dispatch(self, visitor, **kw):
         return self.__element.__class__._compiler_dispatch(self, visitor, **kw)