[FIXED] What is the use of __table_args__ = {'extend_existing': True} in SQLAlchemy?

Issue

I have a flask application which I'm trying to convert into Django. In one of the models which inherit an abstract base model, it is mentioned as

__table_args__ = {'extend_existing': True}

Can someone please explain what this means in SQLAlchemy with a small example.

I have gone through few articles but as I worked on Django and new to Flask-SQLAlchemy I couldn't understand it properly.

https://hackersandslackers.com/manage-database-models-with-flask-sqlalchemy/ https://docs.sqlalchemy.org/en/13/orm/extensions/declarative/table_config.html

Solution

This parameter is to determine wheter this table is allowed to add new columns for its inheriting classes, or to 'extend' so to speak.

For example, I have:

class User(Base):
  __table_args__ = {'extend_existing': True}
  
  attr1 = Column(String)
  attr2 = Column(Integer)

class ChildUser(User):
  attr3 = Column(Integer) # this will allow this column to 'extend' the parent attriubtes.

This parameter is default to 'False', and normally you wouldn't want to change this setting.

Answered By - Jinghui Niu