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)
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?
Best regards
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