1 files changed, 53 insertions, 0 deletions
diff --git a/lib/sqlalchemy/orm/loading.py b/lib/sqlalchemy/orm/loading.py
index 7feec660d..48c0db851 100644
--- a/lib/sqlalchemy/orm/loading.py
+++ b/lib/sqlalchemy/orm/loading.py
@@ -19,6 +19,7 @@ from . import attributes, exc as orm_exc
 from ..sql import util as sql_util
 from . import strategy_options
 from . import path_registry
+from .. import sql
 
 from .util import _none_set, state_str
 from .base import _SET_DEFERRED_EXPIRED, _DEFER_FOR_STATE
@@ -353,6 +354,27 @@ def _instance_processor(
     session_id = context.session.hash_key
     version_check = context.version_check
     runid = context.runid
+
+    if not refresh_state and _polymorphic_from is not None:
+        key = ('loader', path.path)
+        if (
+                key in context.attributes and
+                context.attributes[key].strategy ==
+                (('selectinload_polymorphic', True), ) and
+                mapper in context.attributes[key].local_opts['mappers']
+        ) or mapper.polymorphic_load == 'selectin':
+
+            # only_load_props goes w/ refresh_state only, and in a refresh
+            # we are a single row query for the exact entity; polymorphic
+            # loading does not apply
+            assert only_load_props is None
+
+            callable_ = _load_subclass_via_in(context, path, mapper)
+
+            PostLoad.callable_for_path(
+                context, load_path, mapper,
+                callable_, mapper)
+
     post_load = PostLoad.for_context(context, load_path, only_load_props)
 
     if refresh_state:
@@ -501,6 +523,37 @@ def _instance_processor(
     return _instance
 
 
+@util.dependencies("sqlalchemy.ext.baked")
+def _load_subclass_via_in(baked, context, path, mapper):
+
+    zero_idx = len(mapper.base_mapper.primary_key) == 1
+
+    q, enable_opt, disable_opt = mapper._subclass_load_via_in
+
+    def do_load(context, path, states, load_only, effective_entity):
+        orig_query = context.query
+
+        q._add_lazyload_options(
+            (enable_opt, ) + orig_query._with_options + (disable_opt, ),
+            path.parent, cache_path=path
+        )
+
+        if orig_query._populate_existing:
+            q.add_criteria(
+                lambda q: q.populate_existing()
+            )
+
+        q(context.session).params(
+            primary_keys=[
+                state.key[1][0] if zero_idx else state.key[1]
+                for state, load_attrs in states
+                if state.mapper.isa(mapper)
+            ]
+        ).all()
+
+    return do_load
+
+
 def _populate_full(
         context, row, state, dict_, isnew, load_path,
         loaded_instance, populate_existing, populators):