On Fri, Oct 20, 2017 at 11:05 AM, Simon King <si...@simonking.org.uk> wrote:
> The "is not None" is important when checking a variable that may
> contain a ClauseElement, precisely because ClauseElement defines that
> __bool__ method.
>
> However, in Session.get_bind(), "mapper" is not supposed to contain a
> ClauseElement. It should either be an instance of
> sqlalchemy.orm.mapper.Mapper, or None, in which case "if mapper:" is a
> valid and concise way to write it. Comparing to None might be strictly
> more accurate, but it shouldn't be necessary.
agree, "mapper" means "mapper" and it is not supposed to be a
ClauseElement. This sounds like arguments are not being passed
correctly somewhere. Would need a demonstration script if something
in SQLAlchemy itself is claimed to be making the mistake.
>
> Simon
>
>
>
> On Fri, Oct 20, 2017 at 3:17 PM, Антонио Антуан <a.ch....@gmail.com> wrote:
>> Really, `mapper` contains this: <sqlalchemy.sql.selectable.CTE at
>> 0x7fe673fb0a50; group_getter>. But does it changes something? I already
>> encountered this problem in my code, when I checked sqla-objects existance
>> without "is not None", project was broken. Is it normal to omit that
>> condition in sqlalchemy code?
>>
>> I use:
>>>>> sqlalchemy.__version__
>> '1.0.19'
>>
>> пятница, 20 октября 2017 г., 16:42:23 UTC+3 пользователь Simon King написал:
>>>
>>> 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
>>
>> --
>> 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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