introduce deferred lambdas

The coercions system allows us to add in lambdas as arguments
to Core and ORM elements without changing them at all.   By allowing
the lambda to produce a deterministic cache key where we can also
cheat and yank out literal parameters means we can move towards
having 90% of "baked" functionality in a clearer way right in
Core / ORM.

As a second step, we can have whole statements inside the lambda,
and can then add generation with __add__(), so then we have
100% of "baked" functionality with full support of ad-hoc
literal values.

Adds some more short_selects tests for the moment for comparison.

Other tweaks inside cache key generation as we're trying to
approach a certain level of performance such that we can
remove the use of "baked" from the loader strategies.

As we have not yet closed #4639, however the caching feature
has been fully integrated as of
b0cfa7379cf8513a821a3dbe3028c4965d9f85bd, we will also
add complete caching documentation here and close that issue
as well.

Closes: #4639
Fixes: #5380
Change-Id: If91f61527236fd4d7ae3cad1f24c38be921c90ba

1 files changed, 7 insertions, 0 deletions

diff --git a/lib/sqlalchemy/sql/__init__.py b/lib/sqlalchemy/sql/__init__.py
index a25c1b083..2fe6f35d2 100644
--- a/lib/sqlalchemy/sql/__init__.py
+++ b/lib/sqlalchemy/sql/__init__.py
@@ -46,6 +46,8 @@ from .expression import intersect_all  # noqa
 from .expression import Join  # noqa
 from .expression import join  # noqa
 from .expression import label  # noqa
+from .expression import lambda_stmt  # noqa
+from .expression import LambdaElement  # noqa
 from .expression import lateral  # noqa
 from .expression import literal  # noqa
 from .expression import literal_column  # noqa
@@ -62,6 +64,7 @@ from .expression import quoted_name  # noqa
 from .expression import Select  # noqa
 from .expression import select  # noqa
 from .expression import Selectable  # noqa
+from .expression import StatementLambdaElement  # noqa
 from .expression import Subquery  # noqa
 from .expression import subquery  # noqa
 from .expression import table  # noqa
@@ -106,18 +109,22 @@ def __go(lcls):
     from . import coercions
     from . import elements
     from . import events  # noqa
+    from . import lambdas
     from . import selectable
     from . import schema
     from . import sqltypes
+    from . import traversals
     from . import type_api
 
     base.coercions = elements.coercions = coercions
     base.elements = elements
     base.type_api = type_api
     coercions.elements = elements
+    coercions.lambdas = lambdas
     coercions.schema = schema
     coercions.selectable = selectable
     coercions.sqltypes = sqltypes
+    coercions.traversals = traversals
 
     _prepare_annotations(ColumnElement, AnnotatedColumnElement)
     _prepare_annotations(FromClause, AnnotatedFromClause)