Yeah, I am also thinking about it. As if we want to process object cross threads, we will need to use something like

```python
session.add(obj)
```

to make it works in the other thread. As what I said before, I want to expose SQLAlchemy stuff as less as possible, so by only returning IDs and passing IDs, model API caller doesn't have to deal with session object. 

But anyway, sometimes, I just think too much, it is actually very rare to deal with session object like that. Maybe this is the time to change my practice here.