SQLAlchemy按功能顺序排序

SQLAlchemy按功能顺序排序

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())