I am trying to use a SQLAlchemy hybrid property like this
class Metric(Base):
__tablename__ = 'metric'
id = Column(Integer, primary_key=True)
value = Column(Float, nullable=False)
@hybrid_property
def dominance(self):
return 1 - abs(0.5 - float(self.value))
Now, I use this in my model like this
class MetricModel(BaseModel):
def get_dominance(self):
self.query(Metric).filter(Metric.dominance > 0.5).order_by(Metric.dominance.desc()).limit(2).all()
This is a flask app and it's being called like this
model = MetricModel(db)
with db.session():
print(model.get_dominant_traits())
This gives me an error
TypeError: float() argument must be a string or a number, not 'InstrumentedAttribute'
From the error it looks like there is no result set, hence the failure. I followed the docs here http://docs.sqlalchemy.org/en/latest/orm/extensions/hybrid.html
What should I do differently?
You need to create expression
from sqlalchemy import func
class Metric(Base):
__tablename__ = 'metric'
id = Column(Integer, primary_key=True)
value = Column(Float, nullable=False)
@hybrid_property
def dominance(self):
return 1 - abs(0.5 - self.value)
@dominance.expression
def dominance(cls):
return 1 - func.abs(0.5 - cls.value)