Hi Mike, Thanks so much for the reply and the pointer.
Since I never added anything to the session explicitly, I think I was missing that loading an object implicitly adds that object to the session - which does make sense. Is that right ? thanks again, terry On Monday, June 15, 2015 at 11:26:39 AM UTC-4, Michael Bayer wrote: > > > > On 6/15/15 11:12 AM, T Mark wrote: > > Hi there, > > I have been pulling my hair out on this one. > > I understood that objects make it into the session only due to an > explicit call to add(). > > or if they are associated with a parent object that is added to the > Session via add(), or if they are associated with an object that is already > present in a Session via add(); this also will occur for backrefs, e.g. A > is in the session, B.a is referred to A, B.a has a backref A.bs, therefore > B is now added. This is configurable. > > > But, I seem to be seeing objects being added without my explicitly doing > so. Is this to be expected ? > > > yes. please see: > http://docs.sqlalchemy.org/en/rel_1_0/orm/cascades.html?highlight=cascades > > > > For instance, I want to establish a many-to-many relationship between > two classes: say, for the purposes here, "Person" and "Kid". > > > test=> create table persons (id SERIAL NOT NULL); > test=> CREATE TABLE person_to_kids (person_id INT NOT NULL, kid_id INT > NOT NULL); > test=> create table kids (id SERIAL NOT NULL, name TEXT NOT NULL); > test=> insert into kids (name) VALUES ('Fred'); > test=> insert into kids (name) VALUES ('Barney'); > > person_to_kids = Table('person_to_kids', > Base.metadata, > Column('person_id', Integer, ForeignKey(' > persons.id')), > Column('kid_id', Integer, ForeignKey('kids.id'))) > class Person(Base): > > __tablename__ = 'persons' > id = Column('id', Integer, primary_key = True) > def __init__(self, > kids = []): > > kids = Kid.get_kids(kid_names = kids) > > print("__init__ before kids assignment") > print(session.new) > > """ Assigning to self.kids here seems to add self to session ??? > """ > > self.kids=kids > print("After assignment to self.kids") > print(session.new) > > > class Kid(Base): > __tablename__ = 'kids' > id = Column(Integer, primary_key = True) > name = Column(String) > parents = relationship("Person", > secondary = person_to_kids, > backref="kids") > > def __init__(self, name = None): > self.name = name > > @staticmethod > def get_kids(kid_names = []): > > kids = [] > > for name in kid_names: > # find first kid > target_set = session.query(Kid).filter(Kid.name == > name).first() > kids.append(target_set) > > return kids > > > > What is puzzling me is that, if I have a collection of Kid objects, and > I assign it to the kids collection in a Person, the Person object seems to > be automatically added to the session and marked as pending, even if I have > not added it. > > For instance, if the Persons table is empty: > > test=> select * from persons; > id > ---- > (0 rows) > > > > and I run the following code: > > print(session.new) > obj = Person(kids = ['Barney', 'Fred']) > print("obj has been created") > print(session.new) > session.commit() > > > The output shows that the Person object is added immediately after the > assignment to obj.kids, without any call to session.add() anywhere in the > code: > > IdentitySet([]) > __init__ before kids assignment > IdentitySet([]) > After assignment to self.kids > IdentitySet([<__main__.Person object at 0x7fb6ce447b10>]) > obj has been created > IdentitySet([<__main__.Person object at 0x7fb6ce447b10>]) > > > And indeed, due to the commit() at the end, the person object makes it > into the database: > > test=> select * from persons; > id > ---- > 10 > (1 row) > > > > But, I understood that objects (only) make it into a session by virtue > of being explicitly added. > > So, is this the correct behavior, or am I misunderstanding something ? > > If I'm not misunderstanding this all, the complete code is at > https://github.com/NuggyBuggy/sqlalchemy_question.git . > > Thanks for reading, > terry > -- > 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:>. > To post to this group, send email to sqlal...@googlegroups.com > <javascript:>. > 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 to sqlalchemy+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.
