Ok, I define my situation.
At first, I'm appologizing for my accent :)
I have two databases, postgresql and vertica.
I have some amount of large tables, besides other tables.
Postgres stores only last two hours (or last week, depends on table) of
large tables, vertica stores all other data.
I implemented *SplittedDataQuery*, subclass of *Query*, which used with my
*Session* like *query_cls*.
The subclass overrides *__iter__(), all(), count(), first(), one()* methods.
It has attribute *_base_query*, which refers on *self*, *_pg_query* and
*_vertica_query*.
Before invoking them, *SplittedDataQuery* checks necessity (by whereclause
inside query and `splitting_time` - moment when the data splitted between
databases) of getting data only from Pg, or only from vertica, or from both
with data union.
Data from vertica returns by *_vertica_query*, data from postgres - by
*_pg_query*
*_vertica_query *binds with* SessionVertica.*
all other queries (*_pg_query and _base_query*) binds with *Session*
Function, creates *SessionVertica*, has nothing unusual.
Session for pg creates like this:
def _create_session(self, conn_string, splitted_query_cls=True):
engine = create_engine(conn_string)
from core.splitted_data import SplittedDataQuery
session = ScopedSession(sessionmaker(bind=engine, query_cls=
SplittedDataQuery if splitted_query_cls else Query)) # query_cls choosing
only for SplittedDataQuery._pg_query
return session
There is overrided *all():*
def all(self):
return self._get_result()
Implementation of *_get_result() *looks like this*:*
def _get_result(self):
self._analyze_base_query()
self._split_query()
self._initialize_db_queries()
result = self._vertica_query.all()
if self._needs_to_get_from_pg:
result.extend(self._pg_query.all())
*_db_queries* initialization inside *SplittedDataQuery* class:
def __init_pg_query(self):
original_session = _create_session(config['sqlalchemy'][
'conn_string'], splitted_query_cls=False)
self._pg_query = self._query.filter() \
.with_session(original_session)
def __init_vertica_query(self):
from hasoffers.core.model.meta import SessionVertica
self._vertica_query = self._query.filter() \
.with_session(SessionVertica)
If I don't create *_pg_query* using *splitted_query_cls=**False* (with std
Query class)*, *then _pg_query invokation of methods (*all(), one() *and
other) will always apply overrided methods (because it uses
SplittedDataQuery).
But, if I create* _pg_query *by defined way, it creates new session and,
so, new connection to Postgres.
As you see, I don't want nor the first, neither the second option :)
вторник, 12 июля 2016 г., 13:35:48 UTC+3 пользователь Simon King написал:
> Could you describe what you are trying to achieve? There's nothing
> about Mike's suggestion that means you need to create a new session -
> you can reuse any existing session.
>
> What does your CustomQueryCls do? Perhaps there's another way of doing
> what you want?
>
> Simon
>
> On Tue, Jul 12, 2016 at 11:09 AM, Антонио Антуан <a.ch...@gmail.com
> <javascript:>> wrote:
> > But it means that I should create one more session with one more
> connection
> > to DB. This is not good for me :(
> >
> > понедельник, 11 июля 2016 г., 22:23:11 UTC+3 пользователь Антонио Антуан
> > написал:
> >>
> >> Can I specify query_cls only for a one query? I try to change
> >> query.session._query_cls and, of course, it doesn't work...
> >>
> >> I want to perform something like this:
> >>
> >> query = Session.query(MyModel)...
> >> default_querycls_result = query.all()
> >> custom_querycls_result = query.change_query_cls(CustomQueryCls).all()
> >
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