[PonyORM-list] Retrieve 10 most recent related records

[Alexander Kozlovsky]

Hi Dylan,

I think this is the most efficient way:


class Person(db.Entity):
    id = PrimaryKey(int, auto=True)
    checkouts = Set("Checkout")

    @property
    def recent_checkouts(self):
        return Checkout.select(lambda c: c.person == self) \
                               .order_by(lambda c: desc(c.date))[:10]

class Checkout(db.Entity):
    id = PrimaryKey(int, auto=True)
    person = Required(Person)
    date = Required(date)
    composite_index(person, date)


Note that I defined composite non-unique index on person and date
attributes in Checkout entity. This way DBMS can do filtering and sorting
using just one index.

Regards,
Alexander

On Tue, Nov 11, 2014 at 3:13 AM, Dylan Staley <staley.dylan at gmail.com>
wrote:

> Hi all! I'm using these two models:
>
> class Person(db.Entity):
>     id = PrimaryKey(int, auto=True)
>     checkouts = Set("Checkout")
>
>     @property
>     def recent_checkouts(self):
>         # return 10 most recent checkouts
>
>
> class Checkout(db.Entity):
>     id = PrimaryKey(int, auto=True)
>     person = Required(Person)
>     date = Required(date)
>
> I'd like to be able to call Person.recent_checkouts to get a list of that
> person's ten most recent checkouts. How would I accomplish this in the most
> performant manner?
>
> Best,
> Dylan Staley
>
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>
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