[PonyORM-list] Treating Pony Queries as "sets"

[Alexander Kozlovsky]

Hi Matthew!

Yes, I think it is possible to add such functionality to Pony ORM. This is
not absolutely simple (because queries should be combined in some
intelligent way), but it is doable in all supported SQL engines.

Could you describe your use-case in more detail, for what purpose you plan
to use such query algebra?




On Tue, Jan 28, 2014 at 6:46 PM, Matthew Bell
<matthewrobertbell at gmail.com>wrote:

> Hello,
>
> I think that a useful feature would be treating pony queries as sets,
> which can have set operations applied to them (since they are lazy).
>
> Example:
>
> class Blah(db.Entity):
>   a = Required(int)
>   b = Required(int)
>
> query_1 = Blah.select(lambda blah: blah.a > 5)
> query_2 = Blah.select(lambda blah: blah.b < 10)
>
> Operations could then be possible such as:
>
> query_1 | query_2
> query_1 & query_2
> query_1 - query_2
>
> Is this possible with all SQL engines? I guess a new query object would be
> returned, which can then be executed as normal.
>
> --
> Regards,
>
> Matthew Bell
>
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>
>
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