- UPDATE statements can now be batched within an ORM flush

into more performant executemany() call, similarly to how INSERT
statements can be batched; this will be invoked within flush
to the degree that subsequent UPDATE statements for the
same mapping and table involve the identical columns within the
VALUES clause, as well as that no VALUES-level SQL expressions
are embedded.
- some other inlinings within persistence.py

doc/build/changelog/changelog_10.rst

@@ -16,6 +16,17 @@
 .. changelog::
 	:version: 1.0.0
 
+    .. change::
+        :tags: orm, feature
+
+        UPDATE statements can now be batched within an ORM flush
+        into more performant executemany() call, similarly to how INSERT
+        statements can be batched; this will be invoked within flush
+        to the degree that subsequent UPDATE statements for the
+        same mapping and table involve the identical columns within the
+        VALUES clause, as well as that no VALUES-level SQL expressions
+        are embedded.
+
     .. change::
         :tags: engine, bug
         :tickets: 3163

lib/sqlalchemy/orm/persistence.py

@@ -248,9 +248,10 @@ def _collect_insert_commands(base_mapper, uowtransaction, table,
 
         has_all_pks = True
         has_all_defaults = True
+        has_version_id_generator = mapper.version_id_generator is not False \
+            and mapper.version_id_col is not None
         for col in mapper._cols_by_table[table]:
-            if col is mapper.version_id_col and \
-                    mapper.version_id_generator is not False:
+            if has_version_id_generator and col is mapper.version_id_col:
                 val = mapper.version_id_generator(None)
                 params[col.key] = val
             else:
@@ -305,6 +306,7 @@ def _collect_update_commands(base_mapper, uowtransaction,
         value_params = {}
 
         hasdata = hasnull = False
+
         for col in mapper._cols_by_table[table]:
             if col is mapper.version_id_col:
                 params[col._label] = \
@@ -341,6 +343,7 @@ def _collect_update_commands(base_mapper, uowtransaction,
                 prop = mapper._columntoproperty[col]
                 history = state.manager[prop.key].impl.get_history(
                     state, state_dict,
+                    attributes.PASSIVE_OFF if col in pks else
                     attributes.PASSIVE_NO_INITIALIZE)
                 if history.added:
                     if isinstance(history.added[0],
@@ -381,8 +384,7 @@ def _collect_update_commands(base_mapper, uowtransaction,
                     else:
                         hasdata = True
                 elif col in pks:
-                    value = state.manager[prop.key].impl.get(
-                        state, state_dict)
+                    value = history.unchanged[0]
                     if value is None:
                         hasnull = True
                     params[col._label] = value
@@ -500,41 +502,63 @@ def _emit_update_statements(base_mapper, uowtransaction,
 
     statement = base_mapper._memo(('update', table), update_stmt)
 
-    rows = 0
-    for state, state_dict, params, mapper, \
-            connection, value_params in update:
+    for (connection, paramkeys, hasvalue), \
+        records in groupby(
+            update,
+            lambda rec: (
+                rec[4],
+                tuple(sorted(rec[2])),
+                bool(rec[5]))
+            ):
 
-        if value_params:
-            c = connection.execute(
-                statement.values(value_params),
-                params)
+        rows = 0
+        records = list(records)
+        if hasvalue:
+            for state, state_dict, params, mapper, \
+                    connection, value_params in records:
+                c = connection.execute(
+                    statement.values(value_params),
+                    params)
+                _postfetch(
+                    mapper,
+                    uowtransaction,
+                    table,
+                    state,
+                    state_dict,
+                    c,
+                    c.context.compiled_parameters[0],
+                    value_params)
+                rows += c.rowcount
         else:
+            multiparams = [rec[2] for rec in records]
             c = cached_connections[connection].\
-                execute(statement, params)
+                execute(statement, multiparams)
 
-        _postfetch(
-            mapper,
-            uowtransaction,
-            table,
-            state,
-            state_dict,
-            c,
-            c.context.compiled_parameters[0],
-            value_params)
-        rows += c.rowcount
+            rows += c.rowcount
+            for state, state_dict, params, mapper, \
+                    connection, value_params in records:
+                _postfetch(
+                    mapper,
+                    uowtransaction,
+                    table,
+                    state,
+                    state_dict,
+                    c,
+                    c.context.compiled_parameters[0],
+                    value_params)
 
-    if connection.dialect.supports_sane_rowcount:
-        if rows != len(update):
-            raise orm_exc.StaleDataError(
-                "UPDATE statement on table '%s' expected to "
-                "update %d row(s); %d were matched." %
-                (table.description, len(update), rows))
+        if connection.dialect.supports_sane_rowcount:
+            if rows != len(records):
+                raise orm_exc.StaleDataError(
+                    "UPDATE statement on table '%s' expected to "
+                    "update %d row(s); %d were matched." %
+                    (table.description, len(records), rows))
 
-    elif needs_version_id:
-        util.warn("Dialect %s does not support updated rowcount "
-                  "- versioning cannot be verified." %
-                  c.dialect.dialect_description,
-                  stacklevel=12)
+        elif needs_version_id:
+            util.warn("Dialect %s does not support updated rowcount "
+                      "- versioning cannot be verified." %
+                      c.dialect.dialect_description,
+                      stacklevel=12)
 
 
 def _emit_insert_statements(base_mapper, uowtransaction,
@@ -833,15 +857,12 @@ def _connections_for_states(base_mapper, uowtransaction, states):
         connection_callable = \
             uowtransaction.session.connection_callable
     else:
-        connection = None
+        connection = uowtransaction.transaction.connection(base_mapper)
         connection_callable = None
 
     for state in _sort_states(states):
         if connection_callable:
             connection = connection_callable(base_mapper, state.obj())
-        elif not connection:
-            connection = uowtransaction.transaction.connection(
-                base_mapper)
 
         mapper = _state_mapper(state)
 

test/orm/test_unitofwork.py

@@ -1126,11 +1126,12 @@ class OneToManyTest(_fixtures.FixtureTest):
 
             ("UPDATE addresses SET user_id=:user_id "
              "WHERE addresses.id = :addresses_id",
-             {'user_id': None, 'addresses_id': a1.id}),
+             [
+                {'user_id': None, 'addresses_id': a1.id},
+                {'user_id': u1.id, 'addresses_id': a3.id}
+            ]),
 
-            ("UPDATE addresses SET user_id=:user_id "
-             "WHERE addresses.id = :addresses_id",
-             {'user_id': u1.id, 'addresses_id': a3.id})])
+            ])
 
     def test_child_move(self):
         """Moving a child from one parent to another, with a delete.

test/orm/test_unitofworkv2.py

@@ -131,12 +131,10 @@ class RudimentaryFlushTest(UOWTest):
             CompiledSQL(
                 "UPDATE addresses SET user_id=:user_id WHERE "
                 "addresses.id = :addresses_id",
-                lambda ctx: [{'addresses_id': a1.id, 'user_id': None}]
-            ),
-            CompiledSQL(
-                "UPDATE addresses SET user_id=:user_id WHERE "
-                "addresses.id = :addresses_id",
-                lambda ctx: [{'addresses_id': a2.id, 'user_id': None}]
+                lambda ctx: [
+                    {'addresses_id': a1.id, 'user_id': None},
+                    {'addresses_id': a2.id, 'user_id': None}
+                ]
             ),
             CompiledSQL(
                 "DELETE FROM users WHERE users.id = :id",
@@ -240,12 +238,10 @@ class RudimentaryFlushTest(UOWTest):
             CompiledSQL(
                 "UPDATE addresses SET user_id=:user_id WHERE "
                 "addresses.id = :addresses_id",
-                lambda ctx: [{'addresses_id': a1.id, 'user_id': None}]
-            ),
-            CompiledSQL(
-                "UPDATE addresses SET user_id=:user_id WHERE "
-                "addresses.id = :addresses_id",
-                lambda ctx: [{'addresses_id': a2.id, 'user_id': None}]
+                lambda ctx: [
+                    {'addresses_id': a1.id, 'user_id': None},
+                    {'addresses_id': a2.id, 'user_id': None}
+                ]
             ),
             CompiledSQL(
                 "DELETE FROM users WHERE users.id = :id",
@@ -732,12 +728,11 @@ class SingleCycleTest(UOWTest):
             testing.db, sess.flush, AllOf(
                 CompiledSQL(
                     "UPDATE nodes SET parent_id=:parent_id "
-                    "WHERE nodes.id = :nodes_id", lambda ctx: {
-                        'nodes_id': n3.id, 'parent_id': None}),
-                CompiledSQL(
-                    "UPDATE nodes SET parent_id=:parent_id "
-                    "WHERE nodes.id = :nodes_id", lambda ctx: {
-                        'nodes_id': n2.id, 'parent_id': None}),
+                    "WHERE nodes.id = :nodes_id", lambda ctx: [
+                        {'nodes_id': n3.id, 'parent_id': None},
+                        {'nodes_id': n2.id, 'parent_id': None}
+                    ]
+                    )
             ),
             CompiledSQL(
                 "DELETE FROM nodes WHERE nodes.id = :id", lambda ctx: {