修复：避免首事件间隙锁死锁

shierfeng-fastapi-backend/tests/module_business/test_inventory_dao.py

@@ -284,12 +284,12 @@ class TestInventoryDao(unittest.IsolatedAsyncioTestCase):
         self.assertIn("biz_pallet_event.idempotency_key = 'event-key'", sql)
         self.assertNotIn('FOR UPDATE', sql)
 
-    async def test_add_event_allocates_next_sequence_and_updates_inventory_pointer(self) -> None:
+    async def test_add_event_reads_exact_previous_pointer_and_updates_inventory(self) -> None:
         sequence_result = MagicMock()
         sequence_result.scalar_one.return_value = 4
         sequence_result.scalar_one_or_none.return_value = 4
         self.db.execute.return_value = sequence_result
-        inventory = BizPalletInventory(pallet_id=7, last_event_id=None)
+        inventory = BizPalletInventory(pallet_id=7, last_event_id=40)
         event = BizPalletEvent(pallet_id=99, event_seq=99, idempotency_key='event-key')
         flush_count = 0
 
@@ -311,15 +311,17 @@ class TestInventoryDao(unittest.IsolatedAsyncioTestCase):
         self.assertEqual(2, self.db.flush.await_count)
         statement = self.db.execute.await_args.args[0]
         self.assertTrue(statement.selected_columns[0].compare(BizPalletEvent.event_seq.property.columns[0]))
+        self.assertTrue(statement.get_final_froms()[0].compare(BizPalletEvent.__table__))
         for dialect in (mysql.dialect(), postgresql.dialect()):
             sql = compile_sql(statement, dialect)
             self.assertNotIn('max(', sql.lower())
+            self.assertIn('biz_pallet_event.event_id = 40', sql)
             self.assertIn('biz_pallet_event.pallet_id = 7', sql)
-            self.assertIn('ORDER BY biz_pallet_event.event_seq DESC', sql)
-            self.assertIn('LIMIT 1', sql)
             self.assertIn('FOR UPDATE', sql)
+            self.assertNotIn('ORDER BY', sql)
+            self.assertNotIn('LIMIT', sql)
 
-    async def test_add_first_event_starts_sequence_at_one(self) -> None:
+    async def test_add_first_event_starts_at_one_without_query(self) -> None:
         sequence_result = MagicMock()
         sequence_result.scalar_one.return_value = None
         sequence_result.scalar_one_or_none.return_value = None
@@ -331,6 +333,25 @@ class TestInventoryDao(unittest.IsolatedAsyncioTestCase):
 
         self.assertEqual(1, event.event_seq)
         self.assertEqual(51, inventory.last_event_id)
+        self.db.execute.assert_not_awaited()
+        self.db.add.assert_called_once_with(event)
+        self.assertEqual(2, self.db.flush.await_count)
+
+    async def test_add_event_rejects_missing_previous_pointer_without_write(self) -> None:
+        sequence_result = MagicMock()
+        sequence_result.scalar_one_or_none.return_value = None
+        self.db.execute.return_value = sequence_result
+        inventory = BizPalletInventory(pallet_id=8, last_event_id=50)
+        event = BizPalletEvent(pallet_id=8, idempotency_key='broken-pointer')
+
+        with self.assertRaisesRegex(RuntimeError, '托盘库存事件指针不一致'):
+            await InventoryDao.add_event(self.db, inventory, event)
+
+        self.db.execute.assert_awaited_once()
+        self.db.add.assert_not_called()
+        self.db.flush.assert_not_awaited()
+        self.assertEqual(50, inventory.last_event_id)
+        self.assertIsNone(event.event_seq)
 
 
 class TestOperationDaoReads(unittest.IsolatedAsyncioTestCase):