- simplify PK logic in update for row switch

2 files changed, 9 insertions, 16 deletions

diff --git a/lib/sqlalchemy/orm/mapper.py b/lib/sqlalchemy/orm/mapper.py
index 89c092b58..f22cac329 100644
--- a/lib/sqlalchemy/orm/mapper.py
+++ b/lib/sqlalchemy/orm/mapper.py
@@ -2364,6 +2364,9 @@ class Mapper(InspectionAttr):
 
     @_memoized_configured_property
     def _primary_key_props(self):
+        # TODO: this should really be called "identity key props",
+        # as it does not necessarily include primary key columns within
+        # individual tables
         return [self._columntoproperty[col] for col in self.primary_key]
 
     def _get_state_attr_by_column(
diff --git a/lib/sqlalchemy/orm/persistence.py b/lib/sqlalchemy/orm/persistence.py
index e36f87991..37b696d0f 100644
--- a/lib/sqlalchemy/orm/persistence.py
+++ b/lib/sqlalchemy/orm/persistence.py
@@ -362,29 +362,19 @@ def _collect_update_commands(uowtransaction, table, states_to_update):
             history = state.manager[propkey].impl.get_history(
                 state, state_dict, attributes.PASSIVE_OFF)
 
-            if row_switch and not history.deleted and history.added:
-                # row switch present.  convert a row that thought
-                # it would be an INSERT into an UPDATE, by removing
-                # the PK value from the SET clause and instead putting
-                # it in the WHERE clause.
-                del params[col.key]
-                pk_params[col._label] = history.added[0]
-            elif history.added:
-                # we're updating the PK value.
-                assert history.deleted, (
-                    "New PK value without an old one not "
-                    "possible for an UPDATE")
-                # check if an UPDATE of the PK value
-                # has already occurred as a result of ON UPDATE CASCADE.
-                # If so, use the new value to locate the row.
-                if ("pk_cascaded", state, col) in uowtransaction.attributes:
+            if history.added:
+                if not history.deleted or \
+                    ("pk_cascaded", state, col) in uowtransaction.attributes:
                     pk_params[col._label] = history.added[0]
+                    params.pop(col.key, None)
                 else:
                     # else, use the old value to locate the row
                     pk_params[col._label] = history.deleted[0]
+                    params[col.key] = history.added[0]
             else:
                 pk_params[col._label] = history.unchanged[0]
 
+
         if params or value_params:
             if None in pk_params.values():
                 raise orm_exc.FlushError(