Merge existing query params in baked lazy load

Fixed a long-standing regression that occurred in version
1.0, which prevented the use of a custom :class:`.MapperOption`
that alters the _params of a :class:`.Query` object for a
lazy load, since the lazy loader itself would overwrite those
parameters.   This applies to the "temporal range" example
on the wiki.  Note however that the
:meth:`.Query.populate_existing` method is now required in
order to rewrite the mapper options associated with an object
already loaded in the identity map.  Also, a custom defined
:class:`.MapperOption` will now cause lazy loaders related to
the target object to use a non-baked query by default unless
the :meth:`.MapperOption._generate_cache_key` method is implemented.

Fixed bug where the new :meth:`.baked.Result.with_post_criteria`
method would not interact with a subquery-eager loader correctly,
in that the "post criteria" would not be applied to embedded
subquery eager loaders.   This is related to :ticket:`4128` in that
the post criteria feature is now used by the lazy loader.

Change-Id: I899808734458e25a023142c2c5bb37cbed869479
Fixes: #4128

1 files changed, 8 insertions, 3 deletions

diff --git a/lib/sqlalchemy/ext/baked.py b/lib/sqlalchemy/ext/baked.py
index 9d5704471..86eee831b 100644
--- a/lib/sqlalchemy/ext/baked.py
+++ b/lib/sqlalchemy/ext/baked.py
@@ -240,7 +240,8 @@ class BakedQuery(object):
                     baked_queries.append((k, bk._cache_key, v))
                 del context.attributes[k]
 
-    def _unbake_subquery_loaders(self, session, context, params):
+    def _unbake_subquery_loaders(
+            self, session, context, params, post_criteria):
         """Retrieve subquery eager loaders stored by _bake_subquery_loaders
         and turn them back into Result objects that will iterate just
         like a Query object.
@@ -250,7 +251,10 @@ class BakedQuery(object):
             bk = BakedQuery(self._bakery,
                             lambda sess, q=query: q.with_session(sess))
             bk._cache_key = cache_key
-            context.attributes[k] = bk.for_session(session).params(**params)
+            q = bk.for_session(session)
+            for fn in post_criteria:
+                q = fn(q)
+            context.attributes[k] = q.params(**params)
 
 
 class Result(object):
@@ -329,7 +333,8 @@ class Result(object):
         context.session = self.session
         context.attributes = context.attributes.copy()
 
-        bq._unbake_subquery_loaders(self.session, context, self._params)
+        bq._unbake_subquery_loaders(
+            self.session, context, self._params, self._post_criteria)
 
         context.statement.use_labels = True
         if context.autoflush and not context.populate_existing: