Mike, thank you for the answer.
But I have another problem with deleting the instance.
Even though all instances belong to the same session (it is possible to
push foo instance):
with Session() as session:
b1 = session.query(BarTable).get(1)
b2 = session.query(BarTable).get(1)
foo = FooTable('some_type', [b1, b2])
session.add(foo)
session.commit()
I get this error:
sqlalchemy.orm.exc.StaleDataError: DELETE statement on table 'foo_bar' expected
to delete 1 row(s); Only 2 were matched.
After simple delete ex.:
with Session() as session:
foo = session.query(FooTable).get()
session.delete(foo)
session.commit()
Pls tell how to delete instance with repeated elements in relation.
P.S. It seems the error to be raised implicit, because "ONLY 2 were matched"
понедельник, 19 июля 2021 г. в 16:22:01 UTC+3, Mike Bayer:
> This is all expected behavior, the main reason you're having problems is
> that you are using multiple sessions and mixing their results together.
> If you need to do this, there are few approaches, the most basic being to
> use the merge() method:
> https://docs.sqlalchemy.org/en/14/orm/session_api.html?highlight=session%20merge#sqlalchemy.orm.Session.merge
>
> however the main issue is that you are mixing results from multiple
> sessions, which in the vast majority of cases is unnecessary. The session
> corresponds to working in a single transaction at a time, and you should
> normally be able to complete all the work you have for a particular
> operation within that single scope.
>
> On Mon, Jul 19, 2021, at 8:31 AM, Evgenii wrote:
>
>
> Hello!
> I’m using many-to-many relation, and this relationship bar_list must have
> list of
> instances. Some of them can be repeated (ex. [inst1, inst2, inst1]).
> I attach very simplified code there (all of database interaction is hidden
> under the hood, user accesses database at top level, but this example
> reflects
> my problem).
>
> foo_bar_association = Table(
> 'foo_bar', Base.metadata,
> Column('foo_id', Integer, ForeignKey('foo.id')),
> Column('bar_id', Integer, ForeignKey('bar.id'))
> )
> *class* *FooTable*(Base):
> __tablename__ = 'foo'
>
> id = Column(Integer, primary_key=*True*)
> type = Column(String, nullable=*False*)
>
> bar_list = relationship('BarTable',
> secondary=foo_bar_association,
> lazy='subquery')
>
> *def* *__init__*(self, type_, bar_list):
> self.type = type_
> self.bar_list = bar_list
> *class* *BarTable*(Base):
> __tablename__ = 'bar'
>
> id = Column(Integer, primary_key=*True*)
> name = Column(String, nullable=*False*)
>
> *def* *__init__*(self, name):
> self.name = name
>
> When I pass two exact instances [bar_one, bar_same_one](as a
> relationship) have to be related (before session.close()) to different
> sessions I have this error:
> sqlalchemy.exc.InvalidRequestError: Can't attach instance another instance
> with key is already present in this session.
>
> *with* Session() *as* session:
> bar_one = session.query(BarTable).get(1)
> *with* Session() *as* session:
> bar_same_one = session.query(BarTable).get(1)
> *with* Session() *as* session:
> foo = FooTable('some_type', [bar_one, bar_same_one])
> session.add(foo)
> session.commit()
>
> But I don’t have any error after I create instances in same session:
>
> *with* Session() *as* session:
> bar_one = session.query(BarTable).get(1)
> bar_same_one = session.query(BarTable).get(1)
> *with* Session() *as* session:
> foo = FooTable('some_type', [bar_one, bar_same_one])
> session.add(foo)
> session.commit()
>
> And after:
>
> *with* Session() *as* session:
> foo = FooTable('some_type', [bar_one, bar_one])
> session.add(foo)
> session.commit()
>
> I can make a work around:
>
> 1. Find unique instances in bar_list and replace not unique with unique
> or
> 2. Get all bar_list ids and get all instances in same session before
> adding
> foo instance.
> But both of them are not pure python way and seems to be complicated
> and ugly.
> I hope there is simple alchemy solution (as adding simple attribute in
> relationship)
>
> Python 3.7.10
> SQLAlchemy==1.4.15
>
>
>
>
>
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> SQLAlchemy -
> The Python SQL Toolkit and Object Relational Mapper
>
> http://www.sqlalchemy.org/
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