Don't raise w/ raiseload strategy for many-to-one history in flush

Fixed issue involving ``lazy="raise"`` strategy where an ORM delete of an
object would raise for a simple "use-get" style many-to-one relationship
that had lazy="raise" configured.  This is inconsistent vs. the change
introduced in 1.3 as part of :ticket:`4353`, where it was established that
a history operation that does not expect emit SQL should bypass the
``lazy="raise"`` check, and instead effectively treat it as
``lazy="raise_on_sql"`` for this case.  The fix adjusts the lazy loader
strategy to not raise for the case where the lazy load was instructed that
it should not emit SQL if the object were not present.

Fixes: #4997
Change-Id: I4deb8c129900f28321c4a5c48301db5fe2aedf78

1 files changed, 21 insertions, 4 deletions

diff --git a/lib/sqlalchemy/orm/strategies.py b/lib/sqlalchemy/orm/strategies.py
index 44ef43418..38d379a4c 100644
--- a/lib/sqlalchemy/orm/strategies.py
+++ b/lib/sqlalchemy/orm/strategies.py
@@ -561,9 +561,11 @@ class LazyLoader(AbstractRelationshipLoader, util.MemoizedSlots):
         self.is_aliased_class = inspect(self.entity).is_aliased_class
 
         join_condition = self.parent_property._join_condition
-        self._lazywhere, self._bind_to_col, self._equated_columns = (
-            join_condition.create_lazy_clause()
-        )
+        (
+            self._lazywhere,
+            self._bind_to_col,
+            self._equated_columns,
+        ) = join_condition.create_lazy_clause()
 
         (
             self._rev_lazywhere,
@@ -708,7 +710,22 @@ class LazyLoader(AbstractRelationshipLoader, util.MemoizedSlots):
         ):
             return attributes.PASSIVE_NO_RESULT
 
-        if self._raise_always and not passive & attributes.NO_RAISE:
+        if (
+            # we were given lazy="raise"
+            self._raise_always
+            # the no_raise history-related flag was not passed
+            and not passive & attributes.NO_RAISE
+            and (
+                # if we are use_get and related_object_ok is disabled,
+                # which means we are at most looking in the identity map
+                # for history purposes or otherwise returning
+                # PASSIVE_NO_RESULT, don't raise.  This is also a
+                # history-related flag
+                not self.use_get
+                or passive & attributes.RELATED_OBJECT_OK
+            )
+        ):
+
             self._invoke_raise_load(state, passive, "raise")
 
         session = _state_session(state)