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.
>>>
>>>
>>>
>>> --
>>> SQLAlchemy -
>>> The Python SQL Toolkit and Object Relational Mapper
>>>
>>> http://www.sqlalchemy.org/
>>>
>>> To post example code, please provide an MCVE: Minimal, Complete, and
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>>
>
>
> --
> SQLAlchemy -
> The Python SQL Toolkit and Object Relational Mapper
>
> http://www.sqlalchemy.org/
>
> To post example code, please provide an MCVE: Minimal, Complete, and
> Verifiable Example. See http://stackoverflow.com/help/mcve for a full
> description.
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--
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The Python SQL Toolkit and Object Relational Mapper
http://www.sqlalchemy.org/
To post example code, please provide an MCVE: Minimal, Complete, and Verifiable
Example. See http://stackoverflow.com/help/mcve for a full description.
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