text: Title: There are two instances of different models. If one instance executes db.session.commit (), the other instance immediately print (obj .__ dict__) will be empty.
  Body: ---
  
  ### Expected behavior
  model .__ dict__ Fields where data can be obtained
  
  ```sh
  root@c57f84919524:/webroot# python manage.py shell
  >>> from app.models import *
  >>> u = User.query.filter().first()
  >>> img = ProjectImages.query.filter().first()
  >>> print(img.__dict__)
  {'_sa_instance_state': <sqlalchemy.orm.state.InstanceState object at 0x7f5b40df7040>, 'id': 1, 'created_at': datetime.datetime(2020, 2, 20, 21, 34, 14), 'image': 'https://cdn.yttys.com/item_1520582553119_0649002690.jpg', 'project_id': 1, 'delete_flag': 0, 'sort': 1}
  >>> from app import db
  >>> db.session.add(u)
  >>> db.session.commit()
  >>> print(img.__dict__)
  {'_sa_instance_state': <sqlalchemy.orm.state.InstanceState object at 0x7f5b40df7040>}
  >>> 
  ```
  
  ### Actual behavior
  ```python
  obj = model.query.filter().first()
  
  other = model2.query.filter().first()
  
  db.session.add(other)
  
  db.session.commit()
  
  print(obj .__ dict__)
  ```
  The final output is:
  ```
  dict_keys (['_ sa_instance_state'])
  ```
  
  There are two instances of different models. If one instance executes db.session.commit (), the other instance immediately print (obj .__ dict__) will be empty.
  
  ### surroundings
  
  * operating system:
  * Python version: 3.8.1
  * Flask-SQLAlchemy version: 2.4.1
  * SQLAlchemy version: 1.3.13