class SimCustomerStat(Base):

__tablename__ = 'sim_customer_stat'
id = Column(Integer, primary_key=True)
sim_id = Column(Integer, ForeignKey('simulation.id'))
simulation = relationship('Simulation', back_populates='customer_stats')
customer_id = Column(Integer, ForeignKey('customer.id'))
customer = relationship('Customer', back_populates='sim_stats')
n = Column(Integer, nullable=False, default=0)
stat_type = Column(String, nullable=False)
cust_quals = relationship('SimQualStat', back_populates='customer_stat',
                          foreign_keys=[SimQualStat.customer_stat_id])

@hybrid_property
def ct(self):
    return sum([qual.ct*qual.n for qual in self.cust_quals])

@ct.expression
def ct(cls):
    return select([func.sum(SimQualStat.ct*SimQualStat.n)])
        .where(SimQualStat.customer_stat_id == cls.id).label('customer_ct')


class SimQualStat(Base):

__tablename__ = 'sim_qual_stat'
id = Column(Integer, primary_key=True)
sim_id = Column(Integer, ForeignKey('simulation.id'))
simulation = relationship('Simulation', back_populates='qual_stats', foreign_keys=[sim_id])
stat_type = Column(String, nullable=False)
customer_stat_id = Column(Integer, ForeignKey('sim_customer_stat.id'))
customer_stat = relationship('SimCustomerStat', back_populates='cust_quals', foreign_keys=[customer_stat_id])
n = Column(Integer, nullable=False, default=0)
ct = Column(Float, nullable=False, default=0)