On Tue, Jan 2, 2018 at 12:06 PM, Tim Chen <timch...@gmail.com> wrote:
> Ah yes, makes sense. So there is a slight difference in that add() will
> modify the original object, while merge() will not. Thanks for the
> explanation!
>
> It would be great if this difference could be added to the docs here
> http://docs.sqlalchemy.org/en/latest/orm/session_api.html#sqlalchemy.orm.session.Session.merge
it's the last sentence of the first paragraph:
The resulting target instance is then returned by the method; the
original source instance is left unmodified, and un-associated with
the Session if not already.
the method could use a quick code example duplicating that of the
"Merging" link right below
(http://docs.sqlalchemy.org/en/latest/orm/session_state_management.html#unitofwork-merging)
, the idea is people would have clicked that link to have an in-depth
understanding of what merging is.
>
> On Tuesday, January 2, 2018 at 11:47:06 AM UTC-5, Mike Bayer wrote:
>>
>> On Tue, Jan 2, 2018 at 11:44 AM, Tim Chen <timc...@gmail.com> wrote:
>> > Hrmm, that's not what I'm getting. Maybe I'm misunderstanding something
>> > -
>> > here's a simple test to illustrate my example. test_add() works as
>> > expected, test_merge() fails.
>> >
>> >
>> > import sqlalchemy as sa
>> > from sqlalchemy.orm import sessionmaker
>> > from sqlalchemy.ext.declarative import declarative_base
>> >
>> > Base = declarative_base()
>> >
>> >
>> > class User(Base):
>> > __tablename__ = 'user'
>> > id = sa.Column(sa.Integer, primary_key=True)
>> > email = sa.Column(sa.Text)
>> > profile = sa.orm.relationship('Profile', uselist=False,
>> > single_parent=True)
>> >
>> >
>> > class Profile(Base):
>> > __tablename__ = 'profile'
>> > id = sa.Column(sa.Integer, primary_key=True)
>> > user_id = sa.Column(sa.Integer, sa.ForeignKey('user.id'),
>> > nullable=False)
>> > interests = sa.Column(sa.Text)
>> >
>> >
>> > engine = sa.create_engine('postgresql://localhost/test')
>> > Base.metadata.create_all(engine)
>> > session = sessionmaker(bind=engine)()
>> >
>> >
>> > def create_user():
>> > return User(
>> > email='f...@bar.com',
>> > profile=Profile(interests='Cooking, Dancing'),
>> > )
>> >
>> >
>> > def test_merge():
>> > user = create_user()
>> > session.merge(user)
>>
>> yep...here's how to use merge:
>>
>>
>> merged_user = session.merge(user)
>>
>>
>> why the return value? because there might already be an object in the
>> session that matches the primary key you might be giving.
>>
>> original user object is untouched
>>
>>
>>
>> > session.commit()
>> >
>> > assert user.id
>> > assert user.profile.id
>> >
>> >
>> > def test_add():
>> > user = create_user()
>> > session.add(user)
>> > session.commit()
>> >
>> > assert user.id
>> > assert user.profile.id
>> >
>> >
>> > test_add()
>> > test_merge()
>> >
>> >
>> > On Monday, January 1, 2018 at 9:49:55 PM UTC-5, Mike Bayer wrote:
>> >>
>> >> On Mon, Jan 1, 2018 at 9:18 PM, Tim Chen <timc...@gmail.com> wrote:
>> >> > When I merge() an object without a PK, I expect similar behavior to
>> >> > add(),
>> >> > in that the autogenerated PK is returned and set on the object. Is
>> >> > that
>> >> > not
>> >> > expected behavior?
>> >>
>> >> it is, assuming the Session has flushed.
>> >>
>> >> >
>> >> > --
>> >> > 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/
>> >
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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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