Hello,
Ok, thank you for the answer. I will try to look into that deeper then.
Best regards
W dniu środa, 25 września 2013 02:51:06 UTC+2 użytkownik Michael Bayer
napisał:
>
>
> On Sep 23, 2013, at 8:13 AM, Piotr Deszyński
> <desz...@red-sky.pl<javascript:>>
> wrote:
>
> I'm tryign to do a bulk update using sqlalchemy ShardedSession. I've
> stumbled on a problem when i have to do a bulk update without selecting
> rows from a database. Here's how I've tried to do it:
>
> class Row(Base, object): #pylint: disable=I0011, R0903
> '''
> Row
> '''
>
> __tablename__ = 'my_table'
>
> some_primary = Column(Integer(11), primary_key=True)
> sharded_attribute = Column(String())
> updated_attribute = Column(Integer(2))
> Session =
> scoped_session(sessionmaker(class_=ShardedSession))Session.configure(
> query_chooser=lambda x: SHARDS_LIST,
> id_chooser=lambda x, y: SHARDS_LIST,
> shard_chooser=my_shard_chooser,
> autocommit=False)
>
> Then I'm making a query as follows:
>
> session.query(Row) \
> .filter_by(Row.sharded_attribute.in_(attributes_list)) \
> .update({Row.updated_attribute: 1}, synchronize_session=False)
>
>
> the current implementation for ShardedQuery doesn't have support for the
> update() or delete() methods. Those methods were added to Query long after
> ShardedQuery was developed, and implementing them transparently is slightly
> non-trivial (essentially has to emit the UPDATE or DELETE across all shards
> that apply to the query_chooser, in the same way that
> _execute_and_instances does).
>
> So the problem is, that sharded_attribute can be a list of rows which are
> in different shards. Using such a query SQLAlchemy calls my_shard_chooser.
> In this function I'm determining a shard or a shard list depending on the
> params. There's a problem during the bulk update thought, becauseinstance
> param
> is None, so I don't have value of sharded_attribute. In that case there's
> passed clause attribute, so using it I'm able to determine what values of
> sharded_attribute were provided. Sadly these items might be in different
> shards and I cannot return a list of shards ids (only single id is
> supported).
>
> Does anybody know how I can change my approach to make it working? Do I
> have to resign from using a session? Is there at all a way to do it other
> than doing firstly select for all updated rows and then updating objects
> and calling commit or making direct calls on engine's execute?
>
>
> If I'm understanding correctly this is all due to update()/delete() not
> being implemented. Looking at how these work right now, there's not a
> straightforward path to override how they execute queries the way
> _execute_and_instances() does, so you might be better off implementing your
> own update()/delete() that's similar to how
> ShardedQuery._execute_and_instances works, but uses core table.update() and
> table.delete() constructs.
>
>
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