I ended up settling for this: @hybrid_property
def ancestors(self): session = inspect(self).session cte = session.query(P2B) \ .filter(P2B.id == self.id) \ .cte(name='cte', recursive=True) cte = cte.union( session.query(P2B) .filter(P2B.id == cte.c.parent_id) ) return session.query(cte).all() And each time I call child.ancestors, the SQL CTE RECURSIVE is issued (of course!?) Thanks again for all your help Mike! On Friday, June 8, 2018 at 6:39:05 PM UTC-5, HP3 wrote: > > BTW, the solution of `.params(child_id=child_id)` you provided worked > perfectly - forgot to mentioned earlier. > It issued the recursive CTE I wanted. > > I still need to ponder if I can simply live with a plain select().cte() > within a vanilla method or @hybrid_property or @hybrid_method, all except > @hybrid_property.expression as in the latter the "caller" would need to > remember to bind `child_id` explicitly and forfeit the usage of `filter( > ancs.c.id==child_id)` > > Thank you very much again Mike !!!! > > On Friday, June 8, 2018 at 6:06:54 PM UTC-5, Mike Bayer wrote: >> >> On Fri, Jun 8, 2018 at 6:59 PM, HP3 <henddher...@gmail.com> wrote: >> > :( >> > >> > Basically, I was trying to prevent the SQL Select for each >> child-to-parent >> > loop-iteration when navigating the tree from leaf to root because I >> figured >> > I could use CTE recursive as @hybrid_property.expression. >> > >> > I was trying to take full advantage of @hybrid_property.expression like >> the >> > examples in >> > >> http://docs.sqlalchemy.org/en/latest/orm/extensions/hybrid.html#join-dependent-relationship-hybrid >> >> > and >> > >> http://docs.sqlalchemy.org/en/latest/orm/extensions/hybrid.html#module-sqlalchemy.ext.hybrid >> >> > The examples show that self/cls is magically chosen depending on the >> > context. >> > >> > Seems like I will end up having *limited* functionality for my >> > `@hybrid_property.expression` as I would have to pass the extra param >> > `cls_id` explicitly. >> > >> > I was hoping that >> `dbsession.query(P2B.ancestors).filter(P2B.id==mychildid)` >> > would automagically bind 'mychildid' to `cls.id` within the >> > @ancestors.expression. >> > Perhaps such is possible some other way? >> >> a hybrid is just a function to give you a component of SQL. if you >> want to change the inside of it, then you need to send a parameter on >> the inside or do a transformation of it. I guess you could run a >> transform, which is what the lazy loader does, e.g. looks for where >> something like "cls.id" is and then replaces it but this is very >> specialized, it wouldn't look any nicer from the calling point of >> view. >> >> >> >> >> > >> > Another catch is that by issuing the manual CTE, the session would >> always >> > issue the SQL and never returned previously loaded ancestors. >> > >> > root >> > / \ >> > c1 c2 >> > >> > c1.ancestors and c2.ancestors will each issue SQL recursive CTE ... >> right? >> > >> > >> > On Friday, June 8, 2018 at 5:33:08 PM UTC-5, Mike Bayer wrote: >> >> >> >> On Fri, Jun 8, 2018 at 5:14 PM, HP3 <henddher...@gmail.com> wrote: >> >> > Thank you so much Mike >> >> > >> >> > >> >> > I am trying to write @ancestors.expression to produce a SQL like >> this: >> >> > >> >> > WITH RECURSIVE scte(id, parent_id) AS >> >> > >> >> > (SELECT p2bases.id AS id, p2bases.parent_id AS parent_id >> >> > >> >> > FROM p2bases >> >> > >> >> > WHERE p2bases.id = %(id_1)s --- This is the param I need at runtime >> >> > (cls.id) >> >> > >> >> > UNION SELECT p2bases.id AS id, p2bases.parent_id AS parent_id >> >> > >> >> > FROM p2bases, scte >> >> > >> >> > WHERE p2bases.id = scte.parent_id) >> >> > >> >> > SELECT scte.id >> >> > >> >> > FROM scte >> >> >> >> >> >> you'd have to put the parameter inside the CTE then, here's one way: >> >> >> >> @ancestors.expression >> >> def ancestors(cls): >> >> cte = select([P2B.id, P2B.parent_id]) \ >> >> .where(P2B.id == bindparam("cls_id")) \ >> >> .cte(name='cte', recursive=True) >> >> cte = cte.union( >> >> select([P2B.id, P2B.parent_id]) >> >> .where(P2B.id == cte.c.parent_id) >> >> ) >> >> return cte >> >> >> >> >> >> then you do: >> >> >> >> dbsession.query(P2B.ancestors).params(cls_id=child_id).all() >> >> >> >> >> >> but note that you always need to provide params(cls_id=x) in that >> case. >> >> >> >> >> >> >> >> > >> >> > >> >> > >> >> > >> >> > Here is the @hybrid_property.expression >> >> > >> >> > @ancestors.expression >> >> > >> >> > def ancestors(cls): >> >> > >> >> > cte = select([P2B.id, P2B.parent_id]) \ >> >> > >> >> > .where(P2B.id == cls.id) \ # <<<<<<< I cannot figure >> out how >> >> > make cls.id the param >> >> > >> >> > .cte(name='cte', recursive=True) >> >> > >> >> > cte = cte.union( >> >> > >> >> > select([P2B.id, P2B.parent_id]) >> >> > >> >> > .where(P2B.id == cte.c.parent_id) >> >> > >> >> > ) >> >> > >> >> > return cte >> >> > >> >> > >> >> > I tried alias, aliased and bindparam in multiple ways >> unsuccessfully. >> >> > >> >> > >> >> > The SQL that is coming out doesn't set the first (cte anchor) WHERE >> >> > clause >> >> > with the bound param id_1 (cls.id in the @ancestors.expression). >> >> > Instead, is the column again? >> >> > >> >> > WITH RECURSIVE cte(id, parent_id) AS >> >> > >> >> > (SELECT p2bases.id AS id, p2bases.parent_id AS parent_id >> >> > >> >> > FROM p2bases >> >> > >> >> > WHERE p2bases.id = p2bases.id -- <<<< I can't figure out how to >> make >> >> > expr.left 'cls.id' from the @ancestors.expression >> >> > >> >> > UNION SELECT p2bases.id AS id, p2bases.parent_id AS parent_id >> >> > >> >> > FROM p2bases, cte >> >> > >> >> > WHERE p2bases.id = cte.parent_id) >> >> > >> >> > SELECT cte.id AS cte_id, cte.parent_id AS cte_parent_id >> >> > >> >> > FROM cte >> >> > >> >> > WHERE cte.id = %(id_1)s >> >> > >> >> > >> >> > >> >> > The correct SQL comes out when I do this: >> >> > >> >> > scte = select([P2B.id, P2B.parent_id]) \ >> >> > >> >> > .where(P2B.id == child_id) \ >> >> > >> >> > .cte(name='scte', recursive=True) >> >> > >> >> > scte = scte.union( >> >> > >> >> > select([P2B.id, P2B.parent_id]).where(P2B.id == >> >> > scte.c.parent_id)) >> >> > >> >> > s = select([scte.c.id]) >> >> > >> >> > ancestors = dbsession.execute(s).fetchall() >> >> > >> >> > >> >> > But I don't know how to integrate that into my @ancestors.expression >> >> > >> >> > I want `child_id` to get the value of `cls.id` when the >> @hybrid_property >> >> > is >> >> > called for the class. >> >> > >> >> > >> >> > >> >> > >> >> > On Friday, June 8, 2018 at 1:48:55 PM UTC-5, Mike Bayer wrote: >> >> >> >> >> >> the example is huge can you point out which two queries you'd like >> to >> >> >> compare? >> >> >> >> >> >> this: >> >> >> cte = dbsession.query(P2B.id, P2B.parent_id) \ >> >> >> .filter(P2B.id == child_id) \ >> >> >> .cte(name='cte', recursive=True) >> >> >> cte = cte.union( >> >> >> dbsession.query(P2B.id, P2B.parent_id).filter( >> >> >> P2B.id == cte.c.parent_id)) >> >> >> cteids = dbsession.query(cte.c.id) >> >> >> ancestors = >> >> >> dbsession.query(P2B).filter(P2B.id.in_(cteids)).all()[1:] >> >> >> >> >> >> >> >> >> and this? >> >> >> >> >> >> ancestors = dbsession.query( >> >> >> P2B.ancestors).filter(P2B.id == child_id).all() # <<<< >> >> >> child_id IS NEVER USED IN EXPRESSION >> >> >> >> >> >> >> >> >> >> >> >> it might surprise you to know I barely follow what these queries >> are >> >> >> returning for you, I just look very briefly to get the desired >> syntax >> >> >> right, so a simple "here's teh code hre's the SQL" is best >> >> >> >> >> >> >> >> >> >> >> >> On Fri, Jun 8, 2018 at 2:44 PM, HP3 <henddher...@gmail.com> wrote: >> >> >> > Ahhhh!!! Makes perfect sense! >> >> >> > >> >> >> > But there is something still amiss ... >> >> >> > The last 2 assertions are triggering because the query is >> returning a >> >> >> > single >> >> >> > ancestor (self) instead of the whole recursive list. >> >> >> > >> >> >> > See the plain CTE and the @hybrid_property.expression CTE: The >> where >> >> >> > clauses >> >> >> > are still different :( >> >> >> > (and hence the output) >> >> >> > >> >> >> > Are my @hybrid_property.expressions incorrectly declared? >> >> >> > >> >> >> > >> >> >> > CTE ---------------------------------------- >> >> >> > >> >> >> > 2018-06-08 13:14:44,144 INFO sqlalchemy.engine.base.Engine BEGIN >> >> >> > (implicit) >> >> >> > >> >> >> > 2018-06-08 13:14:44,145 INFO sqlalchemy.engine.base.Engine WITH >> >> >> > RECURSIVE >> >> >> > cte(id, parent_id) AS >> >> >> > >> >> >> > (SELECT p2bases.id AS id, p2bases.parent_id AS parent_id >> >> >> > >> >> >> > FROM p2bases >> >> >> > >> >> >> > WHERE p2bases.id = %(id_1)s UNION SELECT p2bases.id AS >> p2bases_id, >> >> >> > p2bases.parent_id AS p2bases_parent_id >> >> >> > >> >> >> > FROM p2bases, cte >> >> >> > >> >> >> > WHERE p2bases.id = cte.parent_id) >> >> >> > >> >> >> > SELECT p2bases.id AS p2bases_id, p2bases.uuid AS p2bases_uuid, >> >> >> > p2bases.classname AS p2bases_classname, p2bases.position AS >> >> >> > p2bases_position, p2bases.extras AS p2bases_extras, p2bases.val >> AS >> >> >> > p2bases_val, p2bases.time AS p2bases_time, p2bases.parent_id AS >> >> >> > p2bases_parent_id >> >> >> > >> >> >> > FROM p2bases >> >> >> > >> >> >> > WHERE p2bases.id IN (SELECT cte.id AS cte_id >> >> >> > >> >> >> > FROM cte) >> >> >> > >> >> >> > 2018-06-08 13:14:44,146 INFO sqlalchemy.engine.base.Engine >> {'id_1': >> >> >> > 20} >> >> >> > >> >> >> > CTE ANCESTORS <__main__.P2Pg object at 0x10bf94be0> >> >> >> > >> >> >> > CTE ANCESTORS <__main__.P2An object at 0x10bf9a160> >> >> >> > >> >> >> > CTE ANCESTORS <__main__.P2KVP object at 0x10bf9a6a0> >> >> >> > >> >> >> > >> >> >> > >> >> >> > @hybrid_property.expression ANCESTORS CLS >> >> >> > ---------------------------------------- >> >> >> > >> >> >> > 2018-06-08 13:14:44,181 INFO sqlalchemy.engine.base.Engine WITH >> >> >> > RECURSIVE >> >> >> > cte(id, parent_id) AS >> >> >> > >> >> >> > (SELECT p2bases.id AS id, p2bases.parent_id AS parent_id >> >> >> > >> >> >> > FROM p2bases >> >> >> > >> >> >> > WHERE p2bases.id = p2bases.id UNION SELECT p2bases.id AS id, >> >> >> > p2bases.parent_id AS parent_id >> >> >> > >> >> >> > FROM p2bases, cte >> >> >> > >> >> >> > WHERE p2bases.id = cte.parent_id) >> >> >> > >> >> >> > SELECT cte.id AS cte_id, cte.parent_id AS cte_parent_id >> >> >> > >> >> >> > FROM cte >> >> >> > >> >> >> > WHERE cte.id = %(id_1)s >> >> >> > >> >> >> > 2018-06-08 13:14:44,182 INFO sqlalchemy.engine.base.Engine >> {'id_1': >> >> >> > 20} >> >> >> > >> >> >> > @hybrid_property.expression ANCESTORS CLS (20, 5) >> >> >> > >> >> >> > >> >> >> > >> >> >> > >> >> >> > On Friday, June 8, 2018 at 12:27:28 PM UTC-5, Mike Bayer wrote: >> >> >> >> >> >> >> >> On Fri, Jun 8, 2018 at 12:16 PM, HP3 <henddher...@gmail.com> >> wrote: >> >> >> >> > Attached the whole file >> >> >> >> >> >> >> >> OK, removing all the "zope" stuff as well as all the other >> queries >> >> >> >> that aren't noted as failing, I am only looking at this query: >> >> >> >> >> >> >> >> ancestors = dbsession.query(P2B.ancestors).filter(P2B.id == >> >> >> >> child_id).all() # <<<< child_id IS NEVER USED IN EXPRESSION >> >> >> >> >> >> >> >> the problem is that you are re-introducing P2B a second time, >> rather >> >> >> >> than referring to the columns that your CTE returns, it should >> be: >> >> >> >> >> >> >> >> ansc = P2B.ancestors >> >> >> >> ancestors = dbsession.query(ansc).filter(ansc.c.id == >> >> >> >> child_id).all() >> >> >> >> >> >> >> >> this produces SQL that obeys the same form I see at >> >> >> >> https://www.postgresql.org/docs/current/static/queries-with.html. >> >> >> >> >> >> >> >> >> Since P2B.ancestors produces a new selectable each time, you >> need to >> >> >> >> assign it to a variable in order to refer to its set of columns >> >> >> >> without re-introducing it. >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> > >> >> >> >> > >> >> >> >> > On Thursday, June 7, 2018 at 7:01:21 PM UTC-5, HP3 wrote: >> >> >> >> >> >> >> >> >> >> Hello >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> Having difficulty with CTE and @hybrid_property.expression on >> a >> >> >> >> >> adjacency >> >> >> >> >> list model. >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> class P2B(Base): >> >> >> >> >> __tablename__ = 'p2bases' >> >> >> >> >> id = Column(Integer, primary_key=True) >> >> >> >> >> classname = Column(String) >> >> >> >> >> parent_id = Column( >> >> >> >> >> Integer, >> >> >> >> >> ForeignKey('p2bases.id', ondelete='CASCADE'), >> >> >> >> >> index=True >> >> >> >> >> ) >> >> >> >> >> >> >> >> >> >> parent = relationship( >> >> >> >> >> 'P2B', >> >> >> >> >> primaryjoin='P2B.parent_id == P2B.id', >> >> >> >> >> foreign_keys='P2B.id', >> >> >> >> >> uselist=False >> >> >> >> >> ) >> >> >> >> >> >> >> >> >> >> __mapper_args__ = { >> >> >> >> >> 'polymorphic_identity': 'P2B', >> >> >> >> >> 'polymorphic_on': classname >> >> >> >> >> } >> >> >> >> >> >> >> >> >> >> @hybrid_property >> >> >> >> >> def ancestors(self): >> >> >> >> >> _ancestors = [] >> >> >> >> >> parent = self.parent >> >> >> >> >> while parent is not None: >> >> >> >> >> _ancestors.append(parent) >> >> >> >> >> parent = parent.parent >> >> >> >> >> return _ancestors >> >> >> >> >> >> >> >> >> >> @ancestors.expression >> >> >> >> >> def ancestors(cls): >> >> >> >> >> cte = select([P2B.id, P2B.parent_id]) \ >> >> >> >> >> .where(P2B.id == cls.id) \ # <<<<<< Based on >> >> >> >> >> Example1 >> >> >> >> >> .cte(name='cte', recursive=True) >> >> >> >> >> >> >> >> >> >> cte = cte.union( >> >> >> >> >> select([P2B.id, P2B.parent_id]) >> >> >> >> >> .where(P2B.id == cte.c.parent_id) >> >> >> >> >> >> >> >> >> >> ) >> >> >> >> >> return cte >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> The issue I am facing is that the SQL statement for ancestors >> >> >> >> >> expression >> >> >> >> >> becomes this >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> WITH RECURSIVE cte(id, parent_id) AS >> >> >> >> >> >> >> >> >> >> (SELECT p2bases.id AS id, p2bases.parent_id AS parent_id >> >> >> >> >> >> >> >> >> >> FROM p2bases >> >> >> >> >> >> >> >> >> >> WHERE p2bases.id = <a href="http://p2bases.id" >> target="_blank" rel="nofollow" onmousedown="this.href=' >> http://www.google.com/url?q\x3dhttp%3A%2F%2Fp2bases.id\x26sa\x3dD\x26sntz\x3d1\x26usg\x3dAFQjCNFXb6853cCgweqpw68fbajiKFHNJg';return >> >> <http://www.google.com/url?q%5Cx3dhttp%3A%2F%2Fp2bases.id%5Cx26sa%5Cx3dD%5Cx26sntz%5Cx3d1%5Cx26usg%5Cx3dAFQjCNFXb6853cCgweqpw68fbajiKFHNJg';return> >> >> true;" onclick="this.href=' >> http://www.google.com/url?q\x3dhttp%3A%2F%2Fp2bases.id\x26sa\x3dD\x26sntz\x3d1\x26usg\x3dAFQj >> >> <http://www.google.com/url?q%5Cx3dhttp%3A%2F%2Fp2bases.id%5Cx26sa%5Cx3dD%5Cx26sntz%5Cx3d1%5Cx26usg%5Cx3dAFQj> > > -- 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. 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