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() ?
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
> <http://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 <http://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
>
>
>
>
>
>
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> SQLAlchemy -
> The Python SQL Toolkit and Object Relational Mapper
>
> http://www.sqlalchemy.org/
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