if语句在hybrid_property表达式中

Question

I have a hybrid_property that performs some conditional and returns a response. I'd like to be able to query against this field so I've created an expression . However, I'm unsure as to how to write a conditional for this sort of use case.

How do I write an expression that multiplies one of two fields against another based on the result of a conditional?

@hybrid_property
def func(self):
    if self.some_column is True:
        return self.true_column * self.amount
    return self.false_column * self.amount

@func.expression
def func(cls):
    # ???
    return

Answer 1

you can use case expression

from sqlalchemy import case

@func.expression
def func(cls):
    return case(
        [
            (cls.some_column == True, cls.true_column * cls.amount),
        ],
        else_=cls.false_column * cls.amount
    )