On Mon, Feb 12, 2018 at 11:38 AM, Christophe Biocca
<christophe.bio...@gmail.com> wrote:
> Right, I can unpack the relationship between A and B into column expressions
> manually, but this will break for `secondaryjoin` relationships.
> I guess I can unpack those manually as well, by introducing the secondary
> table expression when needed. I will try that.
>
you need to show me a mapping and SQL you want, then I can show you that.
> On 12 February 2018 at 11:24, Mike Bayer <mike...@zzzcomputing.com> wrote:
>>
>> On Sat, Feb 10, 2018 at 6:17 PM, Christophe Biocca
>> <christophe.bio...@gmail.com> wrote:
>> > Let's say I have 2 models, A and B, with relationships A.bs
>> > (haslist=True)
>> > and B.a (haslist=False)
>> >
>> > Doing a semi join is trivial:
>> >
>> > session.query(A).filter(A.bs.any(SomeConditionOnB))
>> > session.query(B).filter(B.a.has(SomeConditionOnA))
>> >
>> > Doing a regular join is also trivial:
>> >
>> > session.query(A).join(A.bs).filter(SomeConditionOnB)
>> > session.query(B).filter(B.a).filter(SomeConditionOnA)
>> >
>> > I'd like to generate the following statement:
>> >
>> > SELECT * FROM a WHERE (EXISTS
>> > (
>> > SELECT 1 FROM b WHERE SomeConditionOnB AND b.a_id = a.id
>> > UNION SELECT 1 FROM b WHERE SomeOtherConditionOnB AND b.a_id =
>> > a.id
>> > )
>> > )
>> >
>> > Because in my case `WHERE EXISTS( foo UNION bar )` is much, much faster
>> > than
>> > `WHERE EXISTS( foo ) OR EXISTS( bar )`.
>> >
>> > I've figured out how do do it as a regular join (with `aliased(B,
>> > b1.union(b2))`) but that won't work (it'll return some rows repeatedly
>> > due
>> > to JOIN's behaviour vs the semijoin of EXISTS).
>> >
>> > `has` and `any` both take a criterion object (?) which means giving it
>> > an
>> > aliased object won't work either.
>> >
>> > I've tried directly using `A.b.expression` and ClauseAdapter based on my
>> > perusing of the source code, but it won't work with tables with
>> > secondary
>> > joins and the like.
>>
>> there's no joins in the statement you describe, you can get that
>> close-to-identical SQL using union() and exists() normally, full
>> example:
>>
>> from sqlalchemy import *
>> from sqlalchemy.orm import *
>> from sqlalchemy.ext.declarative import declarative_base
>> from sqlalchemy.ext.declarative import declared_attr
>>
>> Base = declarative_base()
>>
>>
>> class A(Base):
>> __tablename__ = 'a'
>> id = Column(Integer, primary_key=True)
>> bs = relationship("B")
>>
>>
>> class B(Base):
>> __tablename__ = 'b'
>> id = Column(Integer, primary_key=True)
>> a_id = Column(ForeignKey('a.id'))
>>
>> session = Session()
>>
>>
>> """
>> I'd like to generate the following statement:
>>
>> SELECT * FROM a WHERE (EXISTS
>> (
>> SELECT 1 FROM b WHERE SomeConditionOnB AND b.a_id = a.id
>> UNION SELECT 1 FROM b WHERE SomeOtherConditionOnB AND b.a_id =
>> a.id
>> )
>> )
>> """
>>
>> q = session.query(A).filter(
>> session.query(B.id).filter(B.id > 5).filter(B.a_id ==
>> A.id).correlate(A).
>> union(
>> session.query(B.id).filter(B.id < 10).filter(B.a_id == A.id).
>> correlate(A)
>> ).exists()
>> )
>>
>> print(q)
>>
>>
>> """
>> SELECT a.id AS a_id FROM a WHERE EXISTS
>> (
>> SELECT 1 FROM (
>> SELECT b.id AS b_id FROM b WHERE b.id > :id_1 AND b.a_id =
>> a.id
>> UNION SELECT b.id AS b_id FROM b WHERE b.id < :id_2 AND
>> b.a_id = a.id
>> ) AS anon_1
>> )
>>
>> """
>>
>>
>>
>>
>>
>>
>> >
>> > --
>> > 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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--
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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