For nesting the joins you have to use the join() construct manually, your
example is pretty verbose there, here's a shorter example. Note that
SQLAlchemy has two "join()" functions - one is sqlalchemy.sql.join, the other
is sqlalchemy.orm.join. The main thing you get from orm.join is that you can
use a relationship as the ON clause as in the example below.
from sqlalchemy import Column, ForeignKey, Integer
from sqlalchemy.orm import Session, relationship, join
from sqlalchemy.ext.declarative import declarative_base
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(Integer, ForeignKey('a.id'))
cs = relationship("C")
class C(Base):
__tablename__ = 'c'
id = Column(Integer, primary_key=True)
b_id = Column(Integer, ForeignKey('b.id'))
sess = Session()
j1 = join(B, C, B.cs)
q = sess.query(A).join(j1)
print q
On Aug 10, 2014, at 3:13 AM, mike waites <[email protected]> wrote:
> Hey!
>
> I not sure if this is entirely possible in SQA and i'm more than open to
> suggestions for ways to improve the query itself but im looking to produce
> the following.
>
> https://gist.github.com/mikeywaites/9e7290eaddcf003e4407
>
> The thing in particular i'm having trouble with is the syntax for the nested
> joins. The below doesn't work but i thought it would serve as a start point
> for anyone able to help.
>
> https://gist.github.com/mikeywaites/59476c0fd91301b53697
>
> Some related material i've found:
>
> https://bitbucket.org/zzzeek/sqlalchemy/issue/2120/support-nesting-of-joins-with-joined-eager
> http://docs.sqlalchemy.org/en/rel_0_9/changelog/migration_09.html#right-nested-inner-joins-available-in-joined-eager-loads
>
> So mostly its just the syntax of the nested joins im struggling with at the
> moment. I can't quite nail the alias + nesting combinations!
>
> Again, any suggestions on improving the query overall are more than welcome
> too!!
>
> Thanks!
>
>
>
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