Trying to understand the right way to define a hybridproperty.expression
that references an 'sub-attribute' of a relationship attribute. I have
done it in another case by using the class name of the relationship
attribute (Tire.weight vs. cls.tire.weight) and that's worked OK. But it
begs the question how to do it if that class (Tire) is used in multiple
relationship attributes. How does the .expression discern between the two.
Hopefully the example below explains better than my words probably have.
See the final .expression "weight_of_tires"... how to make it reference the
front_tire attribute and rear_tire attribute - both of the same model class
- distinctly? This sample is using flask-alchemy - hopefully that doesn't
confuse things.
class Tire(db.Model):
__tablename__ = 'tire'
id = Column(Integer, primary_key=True)
weight = Column(Integer)
size = Column(VARCHAR(50))
class Motorcycle(db.Model):
__tablename__ = 'motorcycle'
id = Column(Integer, primary_key=True)
front_tire_id = Column(ForeignKey(Tire.id))
rear_tire_id = Column(ForeignKey(Tire.id))
front_tire = relationship(Tire, foreign_keys=[front_tire_id],
lazy='joined')
rear_tire = relationship(Tire, foreign_keys=[rear_tire_id],
lazy='joined')
@hybrid_property
def weight_of_tires(self):
return self.front_tire.weight + self.rear_tire.weight
@weight_of_tires.expression
def weight_of_tires(cls):
# return Tire.weight + Tire.weight
# return cls.front_tire.weight + cls.rear_tire.weight
--
SQLAlchemy -
The Python SQL Toolkit and Object Relational Mapper
http://www.sqlalchemy.org/
To post example code, please provide an MCVE: Minimal, Complete, and Verifiable
Example. See http://stackoverflow.com/help/mcve for a full description.
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