如何使用sqlalchemy hybrid\u属性查询多个字段？

Question

我的模型定义如下：

class Patch(Base):
    id = Column(Integer, primary_key=True)
    major = Column(Integer, nullable=False)
    minor = Column(Integer, nullable=False)

    @hybrid_property
    def patch(self) -> str:
        return f'{self.major}.{self.minor}'

    @patch.expression
    def patch(self):
        return func.concat(self.major, '.', self.minor)

我想提出这样的请求：

Patch.query.order_by(Patch.patch)

应该等于下一个SQL命令：

SELECT * FROM patch ORDER BY major DESC, minor DESC

我试着用^{}

    @patch.expression
    def patch(self):
        return self.major, self.minor

但有个例外：

sqlalchemy.exc.InvalidRequestError: SQL expression, column, or mapped entity expected - got '(<sqlalchemy.orm.attributes.InstrumentedAttribute object at 0x7f1a5cd5fc50>, <sqlalchemy.orm.attributes.InstrumentedAttribute object at 0x7f1a5cd5fd00>)

我知道可以使用custrom comparator，但是我还没有找到如何使用两个字段（即major，minor）。你知道吗

有什么想法吗？你知道吗

另外，不一定非得是hybrid_property，任何一种方式都可以

Answer 1

下面是两个单独的字段上的排序。值得注意的是，patch的python实现仍然是一个字符串，因此python对象和SQL行之间的顺序会有所不同，除非将patch更改为返回(major, minor)的元组。使用python3.6.5、SQLAlchemy 1.1.15、psycopg2 2.7.7测试

from sqlalchemy import create_engine, Column, Integer, func
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.ext.hybrid import hybrid_property
from sqlalchemy.orm import sessionmaker
from sqlalchemy.sql.functions import concat

engine = create_engine('postgresql://localhost:5432/postgres', echo=True)
Base = declarative_base(bind=engine)


class Patch(Base):

    __tablename__ = "patch"

    id = Column(Integer, primary_key=True)
    major = Column(Integer, nullable=False)
    minor = Column(Integer, nullable=False)

    @hybrid_property
    def patch(self) -> str:
        return f'{self.major}.{self.minor}'

    @patch.expression
    def patch(self):
        return self.major.op(",")(self.minor)

    def __repr__(self):
        return f"Patch object {self.id} {self.patch}"


Base.metadata.create_all()
Session = sessionmaker(bind=engine)
session = Session()

if __name__ == "__main__":
    if session.query(Patch).count() == 0:
        example_patches = [Patch(major=major, minor=minor) for major in range(3) for minor in range(3)]
        session.add_all(example_patches)
        session.commit()

    patches = session.query(Patch).order_by(Patch.patch).all()
    print(patches)

2019-06-13 14:44:27,245 INFO sqlalchemy.engine.base.Engine SELECT patch.id AS patch_id, patch.major AS patch_major, patch.minor AS patch_minor 
  FROM patch ORDER BY patch.major , patch.minor
2019-06-13 14:44:27,245 INFO sqlalchemy.engine.base.Engine {}
[Patch object 2740 0.0, Patch object 2741 0.1, Patch object 2742 0.2, Patch object 2743 0.3, Patch object 2744 0.4, Patch object 2745 0.5, Patch object 2746 0.6, Patch object 2747 0.7, Patch object 2748 0.8, Patch object 2749 0.9, Patch object 2750 0.10, ...