If both the Signal class and the Trade class share the same database columns and the only way they differ is in the methods defined on the classes, then it makes sense to use a single table inheritance model.
As Flask-SQLAlchemy magically defines table names if you don't define them, you'll need to explicitly set the __tablename__ attribute of the child class to None to signal you intention to use the single table construct.
Then, if the objective is to copy the values of the columns of the Signal object over to a new Trade object, then you can iterate over the columns of Signal.__table__ in order to get the values of the column from Signal and write them to the new instance of Trade.
The loop would look something like this:
signal = db.session.query(Signal).one()
new_trade = Trade()
for col in Signal.__table__.c:
if col.key not in ("id", "type"):
setattr(new_trade, col.key, getattr(signal, col.key))
Here's a full working example:
from flask import Flask
from flask_sqlalchemy import SQLAlchemy
app = Flask(__name__)
app.config["SQLALCHEMY_DATABASE_URI"] = "sqlite:///test.db"
app.config["SQLALCHEMY_TRACK_MODIFICATIONS"] = False
db = SQLAlchemy(app)
class Signal(db.Model):
__tablename__ = "signal"
id = db.Column(db.Integer, primary_key=True)
# MAIN FIELDS
type = db.Column(db.String(20))
col1 = db.Column(db.Integer)
col2 = db.Column(db.Integer)
__mapper_args__ = {"polymorphic_on": "type", "polymorphic_identity": "signal"}
class Trade(Signal):
__tablename__ = None
__mapper_args__ = {"polymorphic_identity": "trade"}
if __name__ == "__main__":
db.drop_all()
db.create_all()
db.session.add(Signal(col1=1, col2=2))
db.session.commit()
signal = db.session.query(Signal).one()
new_trade = Trade()
for col in Signal.__table__.c:
if col.key not in ("id", "type"):
setattr(new_trade, col.key, getattr(signal, col.key))
db.session.add(new_trade)
db.session.commit()
db.session.expire_all()
trade = db.session.query(Trade).first()
print(trade.col1, trade.col2)