python - Pony ORM 是否完全支持计算/派生字段？

Question

假设我在 Pony ORM 中有以下架构:

from pony.orm import *

db = Database("postgres", database='foo')

class Job(db.Entity):

    job_id = PrimaryKey(int, auto=True)
    job_name = Required(str)
    base_salary = Required(int)
    multiplier = Required(int, default=1000)
    people = Set(lambda: Person)

class Person(db.Entity):

    person_id = PrimaryKey(int, auto=True)
    name = Required(str)
    job = Required(lambda: Job)
    experience = Required(int)

我希望 Person 实体有一个 salary 属性，它等于:

Job.base_salary + (Person.experience * Job.multiplier)

我的第一个想法是像这样向 Person 实体添加一个属性:

@property
def salary(self):
    return self.job.base_salary + (self.experience * self.job.multiplier)

这适用于一个简单的查询:

j1 = Job(job_name = "Astronaut", base_salary = 80000, multiplier = 5000)
j2 = Job(job_name = "Butcher", base_salary = 40000, multiplier = 2000)
j3 = Job(job_name = "Chef", base_salary = 30000)

for i, name in enumerate(["Alice", "Bob", "Carol"]):
    p = Person(name = name, job=j1, experience = i)

for i, name in enumerate(["Dave", "Erin"]):
    p = Person(name = name, job=j2, experience = i)

for i, name in enumerate(["Frank", "Gwen"]):
    p = Person(name = name, job=j3, experience = i)

for p in select(p for p in Person):
    print p.name, p.experience, p.salary

打印:

Alice 2 90000
Bob 4 100000
Carol 6 110000
Dave 2 44000
Erin 4 48000
Frank 2 32000
Gwen 4 34000    

但是如果我尝试这样的事情:

for j in select((j.job_name, avg(j.people.salary)) for j in Job):
    print j

也许不足为奇，我得到:

AttributeError: j.people.salary

因为 salary 不是“真实”属性。有没有一种方法可以让计算字段被视为可以对其进行正常聚合/计算的一流实体？

Answer 1

感谢您的建议!

目前(2015 年 2 月)Pony ORM 不支持计算字段，但是这个特性可以相对容易地实现，因为 Pony 已经有能力 translate lambdas to SQL .我希望我们能尽快添加计算字段。