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, 7 insertions, 3 deletions

diff --git a/lib/sqlalchemy/engine/cursor.py b/lib/sqlalchemy/engine/cursor.py
index 8d1a1bb57..fdbf826ed 100644
--- a/lib/sqlalchemy/engine/cursor.py
+++ b/lib/sqlalchemy/engine/cursor.py
@@ -57,6 +57,9 @@ class CursorResultMetaData(ResultMetaData):
 
     returns_rows = True
 
+    def _has_key(self, key):
+        return key in self._keymap
+
     def _for_freeze(self):
         return SimpleResultMetaData(
             self._keys,
@@ -1203,6 +1206,7 @@ class BaseCursorResult(object):
 
     out_parameters = None
     _metadata = None
+    _metadata_from_cache = False
     _soft_closed = False
     closed = False
 
@@ -1213,7 +1217,6 @@ class BaseCursorResult(object):
             obj = CursorResult(context)
         else:
             obj = LegacyCursorResult(context)
-
         return obj
 
     def __init__(self, context):
@@ -1247,8 +1250,9 @@ class BaseCursorResult(object):
     def _init_metadata(self, context, cursor_description):
         if context.compiled:
             if context.compiled._cached_metadata:
-                cached_md = context.compiled._cached_metadata
-                self._metadata = cached_md._adapt_to_context(context)
+                cached_md = self.context.compiled._cached_metadata
+                self._metadata = cached_md
+                self._metadata_from_cache = True
 
             else:
                 self._metadata = (