a1.bs only loads something if there's nothing loaded already, or if the value was "expired".
usually, as long as you keep objects associated with a Session, there's no need to worry about it as things load as they are needed. but in that specific example, I'm moving an object from one session to another and trying to trip a condition that only shows up if the object were modified while it's "detached". it isn't a usual thing. On Mar 16, 2014, at 10:45 PM, Bao Niu <niuba...@gmail.com> wrote: > Hi Michael, > > It really works like magic! I mean the refreshing part. What exactly happens > when refreshinga1.bs? Does it actually replace the old b1 inside the > collection with a newer one? I can't wrap my mind around it. And more > importantly, does it mean I should *refresh* every attributes before close a > session, in order to carry their attribute over to the next session? > What is the reason not making such *refreshing* automatic by default??? > > Sorry for bringing up another question here. > > > On Sun, Mar 16, 2014 at 10:58 AM, Michael Bayer <mike...@zzzcomputing.com> > wrote: > > On Mar 15, 2014, at 7:41 PM, Bao Niu <niuba...@gmail.com> wrote: > >> Thanks a lot Michael! Just a trivial question here, I noticed in your first >> reply you used: >> # refresh a1.bs >> >> Why do we need to refresh it? I tried it in my terminal and it doesn't emit >> any sql. Is this one if those secret techniques that differentiate a >> sqlalchemy ninja and a newbie?;) >> >> > > it should emit SQL, because the sess.commit() call above has expired the > collection. in my script it fails down on "a1.bs.remove()" if i don't call > that first. > > > > >> On Mar 15, 2014 8:31 AM, "Michael Bayer" <mike...@zzzcomputing.com> wrote: >> you have every reason to be confused by that paragraph, which is using way >> too much terminology to express what's important there. at some point, we >> had to add a behavior which I thought would be confusing to people, so that >> paragraph tries badly to explain what it is. I should replace it with just >> a simple sentence and an example. Here's the example: >> >> from sqlalchemy import * >> from sqlalchemy.orm import * >> 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')) >> >> e = create_engine("sqlite://", echo=True) >> Base.metadata.create_all(e) >> >> sess = Session(e) >> a1 = A() >> b1 = B() >> >> a1.bs = [b1] >> >> sess.add(a1) >> sess.commit() >> >> a1.bs # refresh a1.bs >> sess.close() # close out - sess is no longer associated with a1, b1 >> >> # all new session >> sess2 = Session(e) >> >> a1.bs.remove(b1) >> >> sess2.add(a1) >> >> # b1 was removed from a1.bs, but >> # is in sess2 anyway! surprising! >> assert b1 in sess2 >> >> # because we need it for the flush, it's still here: >> from sqlalchemy import inspect >> print inspect(a1).attrs.bs.history.deleted >> >> >> >> >> >> >> On Mar 15, 2014, at 5:26 AM, Bao Niu <niuba...@gmail.com> wrote: >> >>> I've read this paragraph >>> (http://docs.sqlalchemy.org/en/latest/orm/session.html#unitofwork-cascades) >>> many many times and still can't think of a practical example of what is >>> being discussed. >>> >>> save-update cascade also cascades the pending history of the target >>> attribute, meaning that objects which were removed from a scalar or >>> collection attribute whose changes have not yet been flushed are also >>> placed into the target session. This is because they may have foreign key >>> attributes present which will need to be updated to no longer refer to the >>> parent. >>> >>> I don't think my English is the main stumbling block here because I >>> understand the meaning of each word, but as soon as I'm putting them >>> together I'm completely lost. Could someone give a simple example here to >>> illustrate the main point in this paragraph please? Highly appreciated. >>> Thanks. >>> >>> -- >>> 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 tosqlalchemy+unsubscr...@googlegroups.com. >>> To post to this group, send email to sqlalchemy@googlegroups.com. >>> Visit this group at http://groups.google.com/group/sqlalchemy. >>> For more options, visit https://groups.google.com/d/optout. >> >> >> -- >> You received this message because you are subscribed to a topic in the >> Google Groups "sqlalchemy" group. >> To unsubscribe from this topic, >> visithttps://groups.google.com/d/topic/sqlalchemy/MSiBcFB3cFI/unsubscribe. >> To unsubscribe from this group and all its topics, send an email >> tosqlalchemy+unsubscr...@googlegroups.com. >> To post to this group, send email to sqlalchemy@googlegroups.com. >> Visit this group at http://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 tosqlalchemy+unsubscr...@googlegroups.com. >> To post to this group, send email to sqlalchemy@googlegroups.com. >> Visit this group at http://groups.google.com/group/sqlalchemy. >> For more options, visit https://groups.google.com/d/optout. > > > -- > You received this message because you are subscribed to a topic in the Google > Groups "sqlalchemy" group. > To unsubscribe from this topic, > visithttps://groups.google.com/d/topic/sqlalchemy/MSiBcFB3cFI/unsubscribe. > To unsubscribe from this group and all its topics, send an email > tosqlalchemy+unsubscr...@googlegroups.com. > To post to this group, send email to sqlalchemy@googlegroups.com. > Visit this group at http://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 tosqlalchemy+unsubscr...@googlegroups.com. > To post to this group, send email to sqlalchemy@googlegroups.com. > Visit this group at http://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. 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