sqlalchemy，混合属性案例陈述人

Question

这是我试图通过sqlalchemy生成的查询

SELECT "order".id AS "id", 
"order".created_at AS "created_at", 
"order".updated_at AS "updated_at", 
CASE 
WHEN box.order_id IS NULL THEN "special" 
ELSE "regular" AS "type"
FROM "order" LEFT OUTER JOIN box ON "order".id = box.order_id

遵循sqlalchemy的文档，我尝试使用hybrid_属性来实现这一点。这就是我目前所掌握的，我没有得到正确的陈述。它没有正确生成case语句。在

^{pr2}$

Answer 1

对于非平凡表达式，hybrid属性必须包含两部分：Python getter和SQL表达式。在本例中，Python端是if语句，SQL端是case expression。在

from sqlalchemy import case
from sqlalchemy.ext.hybrid import hybrid_property


@hybrid_property
def type(self):
    return 'special' if self.order_type else 'regular'

@type.expression
def type(cls):
    return case({True: 'special', False: 'regular'}, cls.order_type)