On Mon, Jul 1, 2019, at 5:20 PM, sector119 wrote:
> For example I have a property 'path' with CTE like this and it wouldn't
> return set of rows, but scalar value as array[] of rows
> would it be possible to load this property as subquery() ?
I don't know from a SQL perspective you'd likely have to use some PG array
function that does that, I don't really use those functions because I don't
really buy into PG's SQL extension culture. But anyway, if you can build a
correlated scalar subquery that returns what you want, use column_property()
and that will get it for you.
I can get the basic idea using func.array():
from sqlalchemy import Column
from sqlalchemy import create_engine
from sqlalchemy import ForeignKey
from sqlalchemy import func
from sqlalchemy import Integer
from sqlalchemy import select
from sqlalchemy import String
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import column_property
from sqlalchemy.orm import relationship
from sqlalchemy.orm import Session
Base = declarative_base()
class A(Base):
__tablename__ = "a"
id = Column(Integer, primary_key=True)
data = Column(String)
bs = relationship("B")
class B(Base):
__tablename__ = "b"
id = Column(Integer, primary_key=True)
a_id = Column(ForeignKey("a.id"))
data = Column(String)
A.b_data = column_property(
func.array(select([B.data]).where(B.a_id == A.id).as_scalar())
)
e = create_engine("postgresql://scott:tiger@localhost/test", echo=True)
Base.metadata.drop_all(e)
Base.metadata.create_all(e)
s = Session(e)
s.add_all(
[A(bs=[B(data="b1"), B(data="b2")]), A(bs=[B(data="b3"), B(data="b4")])]
)
s.commit()
for a1 in s.query(A):
print(a1.b_data)
>
> Of course I can include that CTE query in my query(Locality) using
> subquery(), but it would be cool if I'll be able to "undefer" that property
> somehow like relation )
>
> @property
> def path(self):
> session = object_session(self)
>
> def get_locality_path_q(locality_id):
> parent_q = session.query(Locality).filter(Locality.id ==
> locality_id).cte(recursive=True)
>
> parents = aliased(parent_q)
>
> locality_alias = aliased(Locality)
>
> q = parent_q.union_all(
> session.query(locality_alias).join(parents, locality_alias.id ==
> parents.c.parent_id)
> )
>
> cte = aliased(Locality, q)
>
> return session.query(cte).order_by(cte.id)
>
> return get_locality_path_q(self.id)
>
> вторник, 2 июля 2019 г., 0:03:20 UTC+3 пользователь Mike Bayer написал:
>> I don't know what you mean. is there SQL you know you want or is that the
>> part you want to figure out?
>>
>>
>> On Mon, Jul 1, 2019, at 4:21 PM, sector119 wrote:
>>> Mike, is it possible to load "@property" as subquery? Maybe as
>>> ARRAY[path_item, path_item, ...]
>>>
>>> воскресенье, 30 июня 2019 г., 20:26:42 UTC+3 пользователь Mike Bayer
>>> написал:
>>>>
>>>>
>>>> On Sun, Jun 30, 2019, at 5:37 AM, sector119 wrote:
>>>>> Nice, thanks a lot, Mike, now it works as expected
>>>>
>>>> that's great. the docs are not good here, there's not enough discussion of
>>>> "aliased()" , from_statement() and what they do, also I'm changing some
>>>> details of how they do their work for 1.4 in any case so documentation
>>>> efforts will be needed.
>>>>
>>>>
>>>>
>>>>>
>>>>> @property
>>>>> *def *path(self):
>>>>> session = object_session(self)
>>>>>
>>>>> *def *get_locality_path_q(locality_id):
>>>>> parent_q = session.query(Locality).filter(Locality.id ==
>>>>> locality_id).cte(recursive=*True*)
>>>>>
>>>>> parents = aliased(parent_q)
>>>>>
>>>>> locality_alias = aliased(Locality)
>>>>>
>>>>> q = parent_q.union_all(
>>>>> session.query(locality_alias).join(parents, locality_alias.id
>>>>> == parents.c.parent_id)
>>>>> )
>>>>>
>>>>> cte = aliased(Locality, q)
>>>>>
>>>>> *return *session.query(cte).order_by(cte.id)
>>>>>
>>>>> *return *get_locality_path_q(self.id)
>>>>>
>>>>> воскресенье, 30 июня 2019 г., 1:11:21 UTC+3 пользователь Mike Bayer
>>>>> написал:
>>>>>>
>>>>>>
>>>>>> On Sat, Jun 29, 2019, at 11:24 AM, sector119 wrote:
>>>>>>> Hello,
>>>>>>>
>>>>>>> I have Locality model with 'path' property to get path from 'root' of
>>>>>>> tree to current item, everything works ok, but
>>>>>>> I can't get result as Locality instance list..
>>>>>>> When I use
>>>>>>> *'*object_session(self).query(Locality).from_statement(q).order_by(Locality.id)'
>>>>>>> I get
>>>>>>> sqlalchemy.exc.ArgumentError: from_statement accepts text(), select(),
>>>>>>> and union() objects only.
>>>>>>>
>>>>>>> How can I adopt results to Locality model?
>>>>>>>
>>>>>>>
>>>>>>> *class *Locality(Base):
>>>>>>> __tablename__ = *'localities'
**
** *__table_args__ = {*'schema'*: SYSTEM_SCHEMA}
>>>>>>>
>>>>>>> id = Column(Integer, primary_key=*True*)
>>>>>>> parent_id = Column(Integer, ForeignKey(SYSTEM_SCHEMA +
>>>>>>> *'.localities.id'*))
>>>>>>> name = Column(UnicodeText, nullable=*False*)
>>>>>>> type = Column(Integer, nullable=*False*)
>>>>>>>
>>>>>>> @property
>>>>>>> *def *path(self):
>>>>>>> *def *get_locality_path_q(locality_id):
>>>>>>> top_q = select([
>>>>>>> Locality.id,
>>>>>>> Locality.parent_id,
>>>>>>> Locality.name,
>>>>>>> Locality.type,
>>>>>>> ]).\
>>>>>>> where(Locality.id == locality_id).\
>>>>>>> cte(recursive=*True*)
>>>>>>>
>>>>>>> parents = aliased(top_q)
>>>>>>>
>>>>>>> locality_alias = aliased(Locality)
>>>>>>>
>>>>>>> q = top_q.union_all(
>>>>>>> select([
>>>>>>> locality_alias.id,
>>>>>>> locality_alias.parent_id,
>>>>>>> locality_alias.name,
>>>>>>> locality_alias.type
>>>>>>> ]).select_from(join(locality_alias, parents,
>>>>>>> locality_alias.id == parents.c.parent_id))
>>>>>>> )
>>>>>>>
>>>>>>> *# return object_session(self).query(q).order_by(q.c.id)
** **return
*object_session(self).query(Locality).from_statement(q).order_by(Locality.id)
>>>>>>>
>>>>>>> *return *get_locality_path_q(self.id)
>>>>>>
>>>>>> above, "q" is a CTE, not a SELECT, meaning it's something you can select
>>>>>> FROM, like a table. Call select() to SELECT from it:
>>>>>>
>>>>>> return (
>>>>>> object_session(self)
>>>>>> .query(Locality)
>>>>>> .from_statement(q.select().order_by(q.c.id))
>>>>>> )
>>>>>>
>>>>>>
>>>>>> additionally, from_statement() does not allow further changes to the
>>>>>> statement and the ORDER BY must be in terms of thing you are selecting
>>>>>> from, in this case q.c.id
>>>>>>
>>>>>> your code would be easier if you made use of top_q as a FROM object
>>>>>> rather than a statement:
>>>>>>
>>>>>> lcte = aliased(Locality, q)
>>>>>>
>>>>>> return (
>>>>>> object_session(self)
>>>>>> .query(lcte)
>>>>>> .order_by(lcte.id)
>>>>>> )
>>>>>>
>>>>>>
>>>>>> There's not too many doc examples of how aliased() works with FROM
>>>>>> clauses but the basic idea is at:
>>>>>>
>>>>>> https://docs.sqlalchemy.org/en/13/orm/tutorial.html#selecting-entities-from-subqueries
>>>>>>
>>>>>> https://docs.sqlalchemy.org/en/13/orm/query.html#sqlalchemy.orm.aliased
>>>>>>
>>>>>> A little more on aliased() with CTE is written more for query.cte()
>>>>>> which you could also be using here:
>>>>>>
>>>>>> https://docs.sqlalchemy.org/en/13/orm/query.html?highlight=cte#sqlalchemy.orm.query.Query.cte
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> --
>>>>>>> SQLAlchemy -
>>>>>>> The Python SQL Toolkit and Object Relational Mapper
>>>>>>>
>>>>>>> http://www.sqlalchemy.org/
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>>>>>
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>>>>>
>>>>> http://www.sqlalchemy.org/
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>>>>
>>>
>>> --
>>> SQLAlchemy -
>>> The Python SQL Toolkit and Object Relational Mapper
>>>
>>> http://www.sqlalchemy.org/
>>>
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>>
>
> --
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> The Python SQL Toolkit and Object Relational Mapper
>
> http://www.sqlalchemy.org/
>
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