On Wed, Aug 23, 2017 at 2:01 AM, Антонио Антуан <[email protected]> wrote:
>
>
>
> So, and now we always make queries without shard_id chosing: we always make
> queries on 'default' database. One exception: when we run app on master and
> read statistics from geo-slaves, we point it explicitly:
> "Session.query(...).set_shard_id(NODE_PREFIX)". So, yes, we use sharding
> mechanizm only for that.
>
> My question still the same: can I override "connection_callable" member with
> None on my "ShardedSessionWithDefaultBind" class?
Sure, the ShardedSession is supposed to be more of an example class
that you can hack on and connection_callable is a simple None/
not-None thing that is used when you flush() to get a list of
connections per row, where each connection is decided based on the
sharding conditionals.
>
> Also, if you can advise any other mechanism to make things as simple as we
> have them now (with horizontal_sharding mechanism), it would be great, our
> team will appreciate it :)
My suggestion was that bulk_insert_mappings() / bulk_update_mappings /
bulk_save_objects don't actually make the objects as any part of the
session's state, nor does the existing object state of the session
have any bearing on the operation of bulk_insert/bulk_update other
than being part of the same transaction. So if you don't want to
tinker with the state of your sharded_session, just use a different
Session.
If you have code like this:
some_stuff = my_sharded_session.query(Stuff).filter(...).all()
my_sharded_session.bulk_save_objects(objects)
you could change it to this:
some_stuff = my_sharded_session.query(Stuff).filter(...).all()
ad_hoc_session =
Session(bind=my_sharded_session.connection(shard_id='default'))
ad_hoc_session.bulk_save_objects(objects)
that way you don't have to change the state of my_sharded_session.
It probably doesn't matter much either way, e.g.
session.connection_callable=None or this, assuming there is no
concurrent sharing of the sharded_session instance.
>
>>
>> >
>> > If it can help: I ALWAYS perform UPDATE/INSERT/DELETE and most of SELECT
>> > queries in only one database. So, I wrote such subclass:
>> >
>> >
>> > class ShardedSessionWithDefaultBind(ShardedSession):
>> > def get_bind(self, mapper, shard_id=None, instance=None,
>> > clause=None,
>> > **kw):
>> > if shard_id is None:
>> > shard_id = default_shard_id
>> > return super(ShardedSessionWithDefaultBind,
>> > self).get_bind(mapper,
>> > shard_id, instance, clause, **kw)
>> >
>> >
>> > Maybe I can override "__init__" for my class and write
>> > "self.connnection_callable = None"?
>> > My research of sqlalchemy code didn't make me sure that it is safe
>> > enough.
>> > But I see, that "connection_callable" used only for checking into
>> > "_bulk_insert" and "_bulk_update" functions in
>> > sqlalchemy.orm.persistence
>> > module.
>> > So, if I 100% sure, that I ALWAYS perform INSERT/UPDATE/DELETE queries
>> > in
>> > only one database, can I make it?
>> >
>> > --
>> > 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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>
> --
> 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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--
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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