Merge "Establish future behavior for Session cascade backrefs, bind"

6 files changed, 62 insertions, 15 deletions

diff --git a/lib/sqlalchemy/orm/dependency.py b/lib/sqlalchemy/orm/dependency.py
index 082998ba8..d4680e394 100644
--- a/lib/sqlalchemy/orm/dependency.py
+++ b/lib/sqlalchemy/orm/dependency.py
@@ -1184,7 +1184,7 @@ class ManyToManyDP(DependencyProcessor):
 
         if secondary_delete:
             associationrow = secondary_delete[0]
-            statement = self.secondary.delete(
+            statement = self.secondary.delete().where(
                 sql.and_(
                     *[
                         c == sql.bindparam(c.key, type_=c.type)
diff --git a/lib/sqlalchemy/orm/query.py b/lib/sqlalchemy/orm/query.py
index d991f6229..b8226dfc0 100644
--- a/lib/sqlalchemy/orm/query.py
+++ b/lib/sqlalchemy/orm/query.py
@@ -1291,7 +1291,9 @@ class Query(
          those being selected.
 
         """
+        return self._from_self(*entities)
 
+    def _from_self(self, *entities):
         fromclause = (
             self.with_labels()
             .enable_eagerloads(False)
@@ -2935,7 +2937,7 @@ class Query(
 
         """
         col = sql.func.count(sql.literal_column("*"))
-        return self.from_self(col).scalar()
+        return self._from_self(col).scalar()
 
     def delete(self, synchronize_session="evaluate"):
         r"""Perform a bulk delete query.
diff --git a/lib/sqlalchemy/orm/relationships.py b/lib/sqlalchemy/orm/relationships.py
index d4c5b4665..cb490b7d7 100644
--- a/lib/sqlalchemy/orm/relationships.py
+++ b/lib/sqlalchemy/orm/relationships.py
@@ -408,6 +408,10 @@ class RelationshipProperty(StrategizedProperty):
           will not cascade an incoming transient object into the session of a
           persistent parent, if the event is received via backref.
 
+          .. deprecated:: 1.4 The
+             :paramref:`_orm.relationship.cascade_backrefs`
+             flag will default to False in all cases in SQLAlchemy 2.0.
+
           .. seealso::
 
             :ref:`backref_cascade` - Full discussion and examples on how
diff --git a/lib/sqlalchemy/orm/session.py b/lib/sqlalchemy/orm/session.py
index 01163b8d4..25aedd52d 100644
--- a/lib/sqlalchemy/orm/session.py
+++ b/lib/sqlalchemy/orm/session.py
@@ -1937,16 +1937,34 @@ class Session(_SessionClassMethods):
 
         # now we are in legacy territory.  looking for "bind" on tables
         # that are via bound metadata.   this goes away in 2.0.
+
+        future_msg = ""
+        future_code = ""
+
         if mapper and clause is None:
             clause = mapper.persist_selectable
 
         if clause is not None:
             if clause.bind:
-                return clause.bind
+                if self.future:
+                    future_msg = (
+                        " A bind was located via legacy bound metadata, but "
+                        "since future=True is set on this Session, this "
+                        "bind is ignored."
+                    )
+                else:
+                    return clause.bind
 
         if mapper:
             if mapper.persist_selectable.bind:
-                return mapper.persist_selectable.bind
+                if self.future:
+                    future_msg = (
+                        " A bind was located via legacy bound metadata, but "
+                        "since future=True is set on this Session, this "
+                        "bind is ignored."
+                    )
+                else:
+                    return mapper.persist_selectable.bind
 
         context = []
         if mapper is not None:
@@ -1955,8 +1973,9 @@ class Session(_SessionClassMethods):
             context.append("SQL expression")
 
         raise sa_exc.UnboundExecutionError(
-            "Could not locate a bind configured on %s or this Session"
-            % (", ".join(context))
+            "Could not locate a bind configured on %s or this Session.%s"
+            % (", ".join(context), future_msg),
+            code=future_code,
         )
 
     def query(self, *entities, **kwargs):
diff --git a/lib/sqlalchemy/orm/unitofwork.py b/lib/sqlalchemy/orm/unitofwork.py
index 97eea4864..9c67130ce 100644
--- a/lib/sqlalchemy/orm/unitofwork.py
+++ b/lib/sqlalchemy/orm/unitofwork.py
@@ -21,6 +21,16 @@ from .. import util
 from ..util import topological
 
 
+def _warn_for_cascade_backrefs(state, prop):
+    util.warn_deprecated_20(
+        '"%s" object is being merged into a Session along the backref '
+        'cascade path for relationship "%s"; in SQLAlchemy 2.0, this '
+        "reverse cascade will not take place.  Set cascade_backrefs to "
+        "False for the 2.0 behavior; or to set globally for the whole "
+        "Session, set the future=True flag" % (state.class_.__name__, prop)
+    )
+
+
 def track_cascade_events(descriptor, prop):
     """Establish event listeners on object attributes which handle
     cascade-on-set/append.
@@ -42,11 +52,17 @@ def track_cascade_events(descriptor, prop):
 
             prop = state.manager.mapper._props[key]
             item_state = attributes.instance_state(item)
+
             if (
                 prop._cascade.save_update
-                and (prop.cascade_backrefs or key == initiator.key)
+                and (
+                    (prop.cascade_backrefs and not sess.future)
+                    or key == initiator.key
+                )
                 and not sess._contains_state(item_state)
             ):
+                if key != initiator.key:
+                    _warn_for_cascade_backrefs(item_state, prop)
                 sess._save_or_update_state(item_state)
         return item
 
@@ -101,9 +117,14 @@ def track_cascade_events(descriptor, prop):
                 newvalue_state = attributes.instance_state(newvalue)
                 if (
                     prop._cascade.save_update
-                    and (prop.cascade_backrefs or key == initiator.key)
+                    and (
+                        (prop.cascade_backrefs and not sess.future)
+                        or key == initiator.key
+                    )
                     and not sess._contains_state(newvalue_state)
                 ):
+                    if key != initiator.key:
+                        _warn_for_cascade_backrefs(newvalue_state, prop)
                     sess._save_or_update_state(newvalue_state)
 
             if (
diff --git a/lib/sqlalchemy/testing/fixtures.py b/lib/sqlalchemy/testing/fixtures.py
index 1eac76598..1583147d4 100644
--- a/lib/sqlalchemy/testing/fixtures.py
+++ b/lib/sqlalchemy/testing/fixtures.py
@@ -293,13 +293,14 @@ class TablesTest(TestBase):
                 continue
             if table not in headers:
                 continue
-            cls.bind.execute(
-                table.insert(),
-                [
-                    dict(zip(headers[table], column_values))
-                    for column_values in rows[table]
-                ],
-            )
+            with cls.bind.begin() as conn:
+                conn.execute(
+                    table.insert(),
+                    [
+                        dict(zip(headers[table], column_values))
+                        for column_values in rows[table]
+                    ],
+                )
 
 
 class RemovesEvents(object):