query multiple SQLalchemy ORM - python-3.x

Question

I'm new in SQLalchemy I need to calculate multiple of some price in my one of the table. This is my tables:
class Order(DeclarativeBase):
__tablename__ = 'order'
id = Field(Integer, primary_key=True)
products = relationship("OrderProduct", back_populates="order", lazy='dynamic')
and
class OrderProduct(DeclarativeBase):
__tablename__ = 'order_products'
id = Field(Integer, primary_key=True)
order_id = Column(Integer, ForeignKey('order.id'), nullable=False)
order = relationship("Order", back_populates="products", protected=True)
product_id = Column(Integer, ForeignKey('product.id'), nullable=False)
product = relationship("Product", back_populates="order_product")
quantity = Field(Integer, nullable=False)
and
class Product(DeclarativeBase):
__tablename__ = 'product'
id = Field(Integer, primary_key=True)
price = Field(Integer)
order_product = relationship("OrderProduct", back_populates="product", protected=True)
I want to multiple price with this situation OrderProduct.quantity * Product.price and products in Order table is an array of Products
I write SQL query like this and it works:
SELECT SUM(price*quantity) FROM product
JOIN order_products ON product.id = order_products.product_id
JOIN order ON order_products.order_id = order.id;
I tried to make it in ORM like this but it takes me Product and I can calculate only price without multiple in quantity:
result = 0
for product in Product.query\
.join(OrderProduct).filter(Product.id == OrderProduct.product_id)\
.join(Order).filter(OrderProduct.order_id == self.id):
result = product.price + result
return result
I make this as #hybrid_property and its work well.
I use a framework that name is restfulpy. it has ORM for sqlalchemy, session in this framework is scoped_session, but it gives me SQL query in debuging mode instead of executing the query like this :
sum_price = {Query}SELECT sum(product.price * order_products.quantity) AS sum_1
FROM product JOIN order_products ON product.id = order_products.product_id JOIN "order" ON "order".id = order_products.order_id
WHERE product.id = order_products.product_id AND order_products.order_id = :order_id_1
Well, Can anyone help me out this problem?
with regards

Answer 1

I just realized that SQLalchemy is a great ORM! When you have a relation between two, three or ... tables, SQLalchemy make a join between them and you just query it!
I made it hard for me and my friends :) SQLalchemy is powerful than what I'm thinking!
This is the right answer:
#hybrid_property
def total_price(self):
return DBSession.query(
func.sum(Product.price * OrderProduct.quantity))\
.filter(OrderProduct.product_id == Product.id) \
.filter(OrderProduct.order_id == self.id).scalar()
DBSession is the same with session

Answer 2

from sqlalchemy import func
query = session.query(func.sum(Product.price*OrderProduct.quantity))
.join(OrderProduct).filter(Product.id == OrderProduct.product_id)
.join(Order).filter(OrderProduct.order_id == self.id)