Thank you one more time!
Just in case I leave fixed expression here:
session.execute(
select(Instance).where(Instance.id.in([list_of_ids])),
execution_options={"populate_existing": True}
)
Is there any way to set populate_existing = True for engine or sessionmaker?
вторник, 23 августа 2022 г. в 22:34:23 UTC+3, Mike Bayer:
>
>
> On Tue, Aug 23, 2022, at 3:00 PM, Evgenii wrote:
>
> Thanks a lot!
> I used “vectorized” for sqlalchemy.orm.Session.refresh method and mean
> that it would be nice to use:
>
> session.refresh(instances_list)
>
> that make a single query to database. Instead of:
>
>
>
> do this:
>
> session.execute(
> select(Instance).where(Instance.id.in([list_of_ids]),
> execution_options={"populate_existing": True})
> )
>
> all objects refreshed
>
>
>
> for el in instances_list:
> session.refresh(el)
>
> that make N queries.
>
> like:
>
> res = session.query(InstrumentTable).filter(InstrumentTable.id.in_([id1, id2,
> ..., idn])).all()*# and sort res with given ids order*
>
> is much faster than (especially in low network connections):
>
> instuments = [session.query(InstrumentTable).get(id_) *for* id_ *in* [id1,
> id2, ..., idn]]
>
>
> вторник, 23 августа 2022 г. в 21:04:05 UTC+3, Mike Bayer:
>
>
>
> On Tue, Aug 23, 2022, at 1:50 PM, Evgenii wrote:
>
> Hi there!
>
>
> Please help me to understand:
> I want to make two equal queries, that sends real queries to database each
> time:
>
>
> session.query(InstrumentTable).get(instr_id)
> <some other code>
> session.query(InstrumentTable).get(instr_id)
>
>
> The problem is that second query returns instance from identity_map.
> I know how to hardcode it, but I want a beautiful solution.
>
>
>
> 1. No, I cannot use refresh method, because it is not vectorized
> (this part of code is used in custom vectorized refresh method,
> because in our case each transaction is slow and therefore expensive) -
> having vectorized SA refresh is a perfect solution, but it does not
> exist.
>
>
> "vectorized". googled it, seems to mean "Vectorization is the process of
> converting an algorithm from operating on a single value at a time to
> operating on a set of values at one time. " OK. which would mean that
> get() is also not "vectorized" since it also operates on one value at a
> time...so..not really sure what that means.
>
> Anyway, don't use query.get(), use session.get() and pass populate_existing
>
>
> https://docs.sqlalchemy.org/en/14/orm/session_api.html?highlight=session+get#sqlalchemy.orm.Session.get
>
> session.get(InstrumentTable, id, populate_existing=True)
>
>
>
>
>
>
> 1. rollback make real second query, but it seems to be hardcode.
> 2. session.identity_map._dict = {} hardcode too
> 3. Opening another session hardcode too.
> 4. Using one of AUTOCOMMIT, READ COMMITTED, READ UNCOMMITTED,
> REPEATABLE READ, SERIALIZABLE as isolation_level seems to be a true
> way,
> but none of them does not work as I expect.
>
>
>
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>
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>
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