混合属性是既充当Python属性又充当SQL表达式的特殊方法。只要您的
difficulty函数可以用SQL表示，它就可以像普通列一样用于过滤和排序。
例如，如果按照问题的鹦鹉数来计算难度，如果问题的天数超过30天，则将其乘以十，则可以使用：
from datetime import datetime, timedeltafrom sqlalchemy import Column, Integer, DateTime, casefrom sqlalchemy.ext.hybrid import hybrid_propertyclass Problem(base): parrots = Column(Integer, nullable=False, default=1) created = Column(DateTime, nullable=False, default=datetime.utcnow) @hybrid_property def difficulty(self): # this getter is used when accessing the property of an instance if self.created <= (datetime.utcnow() - timedelta(30)): return self.parrots * 10 return self.parrots @difficulty.expression def difficulty(cls): # this expression is used when querying the model return case( [(cls.created <= (datetime.utcnow() - timedelta(30)), cls.parrots * 10)], else_=cls.parrots )
并查询：
session.query(Problem).order_by(Problem.difficulty.desc())
