On Fri, Oct 20, 2017 at 2:15 PM, Антонио Антуан <a.ch....@gmail.com> wrote:
> Hi.
> I use my own `RoutingSession` and `RoutingQuery` implementation, most of it
> inspired by `sqlalchemy.ext.horizontal_shard`:
>
> class RoutingSession(Session):
> def get_bind(self, mapper=None, clause=None, shard_id=None, **kwargs):
> original_bind = None
> try:
> original_bind = super(RoutingSession, self).get_bind(mapper,
> clause)
> except UnboundExecutionError:
> # may not be bound
> pass
> if shard_id is None:
> shard_id = TenantIDStorage.get_shard_id() # just global storage
> bind_for_shard = self.__binds[shard_id]
> if original_bind is not None and original_bind.url ==
> bind_for_shard.url:
> return original_bind
> else:
> return bind_for_shard
>
> def __init__(self, shards=None, query_cls=CachingQuery,
> engines_factory=None, **kwargs):
> super(RoutingSession, self).__init__(query_cls=query_cls, **kwargs)
> self.__binds = {}
> self.engines_factory = engines_factory
> if shards is not None:
> self.update_shards(**shards)
>
> def _add_bind(self, key, bind):
> self.__binds[key] = bind
>
>
>
>
> class RoutingQuery(Query):
> def __init__(self, *args, **kwargs):
> super(RoutingQuery, self).__init__(*args, **kwargs)
> self._shard_id = TenantIDStorage.get_shard_id()
>
> def get(self, ident):
> self._check_bound_to_shard()
> return super(CachingQuery, self).get(ident)
>
> def _check_bound_to_shard(self):
> if self._shard_id is None:
> raise ValueError('query not bound to any shard')
>
> def _execute_and_instances(self, querycontext):
> self._check_bound_to_shard()
> querycontext.attributes['shard_id'] = self._shard_id
> result = self._connection_from_session(
> mapper=self._mapper_zero(),
> shard_id=self._shard_id).execute(
> querycontext.statement,
> self._params
> )
> return self.instances(result, querycontext)
>
>
>
>
>
>
> Sometimes I got this error:
>
> File "/home/anton/Projects/proj/admin/proj/admin/views/stats.py", line
> 898, in _get_filters_from_request
> control_groups = [g.id for g in
> User.get_own_groups_query(current_user.id)]
> File
> "/home/anton/Projects/proj/.venv/lib/python2.7/site-packages/sqlalchemy/orm/query.py",
> line 2802, in __iter__
> return self._execute_and_instances(context)
> File
> "/home/anton/Projects/proj/core/proj/core/orm_extensions/rouing_session.py",
> line 105, in _execute_and_instances
> shard_id=self._shard_id).execute(
> File
> "/home/anton/Projects/proj/.venv/lib/python2.7/site-packages/sqlalchemy/orm/query.py",
> line 2806, in _connection_from_session
> **kw)
> File
> "/home/anton/Projects/proj/.venv/lib/python2.7/site-packages/sqlalchemy/orm/session.py",
> line 984, in connection
> bind = self.get_bind(mapper, clause=clause, **kw)
> File
> "/home/anton/Projects/proj/core/proj/core/orm_extensions/cachingquery.py",
> line 279, in get_bind
> original_bind = super(RoutingSession, self).get_bind(mapper, clause)
> File
> "/home/anton/Projects/proj/.venv/lib/python2.7/site-packages/sqlalchemy/orm/session.py",
> line 1336, in get_bind
> if mapper and mapper.mapped_table.bind:
> File
> "/home/anton/Projects/proj/.venv/lib/python2.7/site-packages/sqlalchemy/sql/elements.py",
> line 539, in __bool__
> raise TypeError("Boolean value of this clause is not defined")
> TypeError: Boolean value of this clause is not defined
>
>
>
>
> I found that `mapper` in original `get_bind` always checks with `is not
> None` condition. There is only one place where condition omitted: `if mapper
> and mapper.mapped_table.bind...`.
> Possibly it is not correct? Or my code does not do something important?
Are you able to catch this error in a debugger?
I'm going to make a wild guess that "mapper" at this point is some
sort of SQL construct (such as a column object or mapped property),
rather than an actual mapper.
You don't say which version of SQLAlchemy you are using, but since
you've overridden _execute_and_instances, I wonder if you need to use
something like query._bind_mapper() as used by _get_bind_args:
<https://bitbucket.org/zzzeek/sqlalchemy/src/4b22b01ade6f94cc4db2f2040c802067a25d29a4/lib/sqlalchemy/orm/query.py?at=rel_1_1_14&fileviewer=file-view-default#query.py-2872>
Hope that helps,
Simon
--
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http://www.sqlalchemy.org/
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