Hi all,
I need some clarification on the following RemovedIn20Warning
"Pet" object is being merged into a Session along the backref cascade path
for relationship "Person.pets"; in SQLAlchemy 2.0, this reverse cascade will
not take place...
Does it really means that in SA 2.0 the pattern
new_entity = Entity(attached_to_object_id=1)
won't work at all, or instead that the "other end" one-to-many relationship
list won't be automatically updated? If the latter, is there any way to say
"ok, I don't care about the reverse cascade updates in this particular case,
as no further accesses to the one-to-many rels on the other side will happen"?
Some background on my usage: the app I'm upgrading to SA 1.4 is based on
Pyramid and has a generic way to build CRUD pages for a given entity, so
visiting, say
/Person/{person_id}/Pet/add
will present a form (automatically generated by deform) able to create a new
Pet entity linked to the given Person; its generic POST handler determines the
target entity from the request's query string and will basically do
# obtain "owner" ID from the request
owners = {key: value for key in request.matchdict if key.endswith('_id')}
pet = Pet(**owners)
session.add(pet)
# apply form's data
pet.edit(request.POST.items())
session.commit()
This triggers the mentioned SA 1.4 warning when executed with
SQLALCHEMY_WARN_20=1, as the attached snippet exhibits.
I tried several variants, such as using "back_populates" instead of the "old"
backref, but the only pattern that removed the warning has been
owner = session.get(Person, request.matchdict['person_id'])
pet = Pet()
owner.pets.append(pet)
where I surely can get, if needed, but would require implementing more
per-entity specific knowledge (possibly using introspection) into the generic
CRUD machinery, to "convert" from the "person_id" to the name of the "other
side" relationship attribute, in several dozens of places.
Another approach could be configuring all the "one-to-many" relationships as
"viewonly", but that again would require more analysis on the code paths...
So, am I missing something and there is some recommended alternative, or
should I dig into the rabbit's hole?
Thanks in advance for any hint,
ciao, lele.
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SQLAlchemy -
The Python SQL Toolkit and Object Relational Mapper
http://www.sqlalchemy.org/
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from sqlalchemy import (Column, ForeignKey, Integer, MetaData, String, Text, Table,
create_engine, orm)
metadata = MetaData()
Base = orm.declarative_base(metadata=metadata)
class Person(Base):
__tablename__ = 'persons'
id = Column(Integer, primary_key=True)
firstname = Column(String)
class Pet(Base):
__tablename__ = 'pets'
id = Column(Integer, primary_key=True)
name = Column(String)
person_id = Column(Integer, ForeignKey('persons.id'))
person = orm.relationship(Person, backref=orm.backref('pets'))
engine = create_engine('sqlite:///:memory:', echo=True)
session = orm.sessionmaker(bind=engine)()
metadata.create_all(engine)
me = Person(firstname='Lele')
session.add(me)
yaku = Pet(person=me, name='Yaku')
session.add(yaku)
session.commit()
--
nickname: Lele Gaifax | Quando vivrò di quello che ho pensato ieri
real: Emanuele Gaifas | comincerò ad aver paura di chi mi copia.
l...@metapensiero.it | -- Fortunato Depero, 1929.
--
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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