[Python] Django ORM like select query in Pony ORM

I'm now to Pony ORM and I have created my DB models like this:

class RSSSource(db.Entity):
title = Required(str, max_len=100)
link = Required(str, max_len=800)
key = Required(str, max_len=200)
description = Required(str, max_len=800)
is_deleted = Optional(bool, sql_default=False)
rss_content = Set('RSS', reverse='source')
subscriptions = Set("Subscription", reverse='source')

def __str__(self):
return self.title

class RSS(db.Entity):
title = Optional(str, max_len=300)
link = Optional(str, max_len=500)
description = Required(str, max_len=500)
source = Optional("RSSSource", reverse="rss_content")
pub_date = Optional(datetime)
is_deleted = Optional(datetime, sql_default=False)
likes = Set("Like", reverse="rss")

def __str__(self):
return self.title

class User(db.Entity):
first_name = Optional(str, max_len=100)
last_name = Optional(str, max_len=100)
username = Required(str, max_len=200, unique=True)
password = Required(str, max_len=500)
is_deleted = Optional(bool, sql_default=False)
subscriptions = Set("Subscription", reverse="user")
likes = Set("Like", reverse="user")

def __str__(self):
return self.username

class Subscription(db.Entity):
source = Optional("RSSSource", reverse="subscriptions")
user = Optional("User", reverse="subscriptions")
is_deleted = Optional(bool, sql_default=False)



now I want to perform a Django ORM-like select query. something like this:

select user.id
from Subscription where source.key = $key and (is_deleted is null or is_deleted = FALSE)


I couldn't find a way to do this. can anyone help, please?

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