Hi Lele -
It looks like .froms on a simple select() that is against ORM entities is just
broken here, so we can fix that. at the moment it's a one liner but there are
some performance implications that might make it more tricky but you can look
at https://github.com/sqlalchemy/sqlalchemy/issues/5614 where I am tracking
this.
On Sun, Sep 27, 2020, at 11:14 AM, Lele Gaifax wrote:
> Hi all,
>
> I started to take a closer look at the new not-yet-released 1.4b1, adapting
> one of my libraries, metapensiero.sqlalchemy.proxy [1].
>
> As expected only one "side" feature, the async support provided by
> metapensiero.sqlalchemy.asyncio [2], appears to be problematic, but as I do
> not
> currently use in production I deferred the effort to a later time.
>
> A very few other tiny problems arose, but one is tricking me, so I'm asking
> advice.
>
> An helper function, col_by_name [3], tries to find a particular column in a
> selectable, looking first in the set of "exported_columns" (as it is called in
> modern SA), failing that in the "froms" collection. It's main purpose is to
> apply sorters and filters (typically coming from an external source such as a
> web request, so expressed in terms of strings representing field names,
> ordering directions and filter expressions) to a base query.
>
> With SA 1.4b1 I have one single failing test, where the problem is in the way
> the function walks into the internals of the selectable to look for a given
> column. The test is very very simple, and basically wants to distill and
> execute a query like
>
> query([Person.firstname, Person.lastname])
> .filter(or_(Person.firstname.like('%Lele'),
> Person.lastname.like('%Lele')))
>
> given an entity, "Person", a string to search and a subset of the columns that
> shall be considered and extracted.
>
> So, this is the test [4]:
>
> def test_query():
> proxy = ProxiedEntity(Person)
>
> sas = Session()
>
> > res = proxy(sas, query=u"Lele", fields="firstname,lastname,nickname")
>
> where "firstname" and "lastname" are valid columns on the entity [5], while
> "nickname" does not exist and shall be ignored. It is this unknown name that
> causes the col_by_name() function to dig further into the set of "joined"
> tables, should there be any. In this case of course there aren't, since the
> query is on a single entity, but this is the traceback of an AttributeError:
>
> tests/test_orm.py:174:
> ----------------------------
>
> .tox/py38-sa14/lib/python3.8/site-packages/metapensiero/sqlalchemy/proxy/base.py:191:
> in __call__
> start, limit) = self.prepareQueryFromConditionsAndArgs(session,
> conditions, args)
>
> .tox/py38-sa14/lib/python3.8/site-packages/metapensiero/sqlalchemy/proxy/base.py:118:
> in prepareQueryFromConditionsAndArgs
> query = self.filterQueryWithArgs(session, conditions, args)
>
> .tox/py38-sa14/lib/python3.8/site-packages/metapensiero/sqlalchemy/proxy/orm.py:104:
> in filterQueryWithArgs
> query, self.only_cols = apply_filters(query, args)
>
> .tox/py38-sa14/lib/python3.8/site-packages/metapensiero/sqlalchemy/proxy/filters.py:402:
> in apply_filters
> column = col_by_name(stmt, f)
>
> .tox/py38-sa14/lib/python3.8/site-packages/metapensiero/sqlalchemy/proxy/utils.py:59:
> in col_by_name
> for f in query.froms:
>
> .tox/py38-sa14/lib/python3.8/site-packages/sqlalchemy/sql/selectable.py:4548:
> in froms
> return self._compile_state_factory(self, None)._get_display_froms()
>
> .tox/py38-sa14/lib/python3.8/site-packages/sqlalchemy/sql/selectable.py:3622:
> in _get_display_froms
> froms = self.froms
>
> .tox/py38-sa14/lib/python3.8/site-packages/sqlalchemy/util/langhelpers.py:1045:
> in __getattr__
> return self._fallback_getattr(key)
> ----------------------------
>
> self = <sqlalchemy.orm.context.ORMSelectCompileState object at
> 0x7fa8574e8160>, key = 'froms'
>
> def _fallback_getattr(self, key):
> > raise AttributeError(key)
> E AttributeError: froms
>
>
> .tox/py38-sa14/lib/python3.8/site-packages/sqlalchemy/util/langhelpers.py:1019:
> AttributeError
>
> Is this something wrong the function is doing, or is some regression in 1.4?
>
> Thanks a lot for any hint,
> ciao, lele.
>
> [1] https://gitlab.com/metapensiero/metapensiero.sqlalchemy.proxy
> [2] https://gitlab.com/metapensiero/metapensiero.sqlalchemy.asyncio
> [3]
> https://gitlab.com/metapensiero/metapensiero.sqlalchemy.proxy/-/blob/master/src/metapensiero/sqlalchemy/proxy/utils.py#L33
> [4]
> https://gitlab.com/metapensiero/metapensiero.sqlalchemy.proxy/-/blob/master/tests/test_orm.py#L169
> [5]
> https://gitlab.com/metapensiero/metapensiero.sqlalchemy.proxy/-/blob/master/tests/fixture.py#L35
> --
> nickname: Lele Gaifax | Quando vivrò di quello che ho pensato ieri
> real: Emanuele Gaifas | comincerò ad aver paura di chi mi copia.
> l...@metapensiero.it | -- Fortunato Depero, 1929.
>
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http://www.sqlalchemy.org/
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