We're just using core, is there some equivalent?
On Thursday, March 17, 2016 at 3:19:23 PM UTC-6, Mike Bayer wrote:
>
>
>
> On 03/17/2016 04:47 PM, Jonathan Beluch wrote:
> > Background: Using core we have tables defined in a few separate files.
> > Goal: To have column defaults be selectables which reference other
> > tables while avoiding circular imports. To avoid circular imports I
> > cannot always build the selects at import time, they have to be
> > generated inside a function that takes table/col names similar to how
> > FKs work.
> >
> > It seems that a callable for Column.default cannot return an uncompiled
> > statement. Two solutions I see:
> >
> > 1) Use the context provided to default callables to compile the dynamic
> > select statement.
> > 2) Implement something similar to FKs, using all the parent attach
> > events to set .arg to a selectable on a subclass of ColumnDefault.
> >
> > Thoughts?
>
> A column default callable is expected to produce the value that's to be
> embedded into the INSERT values. You can execute any SQL you'd like
> there, but that's after the INSERT statement's string form is already
> decided.
>
> If the goal is that the default is a SQL clause to be embedded in the
> string form of the INSERT, then you use a fixed default that is
> represented by that SQL clause.
>
> If you can't generate that SQL clause due to imports, there's various
> ways to defer the production of the Column but the simplest way, not
> necessarily the nicest, is to stick it in declare_first:
>
> from sqlalchemy import *
> from sqlalchemy.orm import *
> from sqlalchemy.ext.declarative import declarative_base
>
> Base = declarative_base()
>
>
> class B(Base):
> __tablename__ = 'b'
> id = Column(Integer, primary_key=True)
>
> @classmethod
> def __declare_first__(cls):
> cls.b = Column(Integer, default=select([A]).as_scalar())
>
>
> class A(Base):
> __tablename__ = 'a'
> id = Column(Integer, primary_key=True)
>
> e = create_engine("sqlite://", echo=True)
> configure_mappers()
> Base.metadata.create_all(e)
>
> s = Session(e)
> s.add(B())
> s.commit()
>
>
> __declare_first__ is actually just a hook for the before_configured
> event so that's actually using the events in any case.
>
>
>
>
> >
> > --
> > You received this message because you are subscribed to the Google
> > Groups "sqlalchemy" group.
> > To unsubscribe from this group and stop receiving emails from it, send
> > an email to sqlalchemy+...@googlegroups.com <javascript:>
> > <mailto:sqlalchemy+unsubscr...@googlegroups.com <javascript:>>.
> > To post to this group, send email to sqlal...@googlegroups.com
> <javascript:>
> > <mailto:sqlal...@googlegroups.com <javascript:>>.
> > Visit this group at https://groups.google.com/group/sqlalchemy.
> > For more options, visit https://groups.google.com/d/optout.
>
--
You received this message because you are subscribed to the Google Groups
"sqlalchemy" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to sqlalchemy+unsubscr...@googlegroups.com.
To post to this group, send email to sqlalchemy@googlegroups.com.
Visit this group at https://groups.google.com/group/sqlalchemy.
For more options, visit https://groups.google.com/d/optout.
