On 4/14/15 3:55 AM, Юрий Пайков wrote:
My question is when I have in a session a newly created object(doesn't
have primary key yet, but will obtain it upon flush) and I merge to
that session another object referring to the first one by relationship
(/b/ in the example) SQLAlchemy doesn't populate latter object with
the primary key from the former. Instead it just generate next value
from the sequence. Why is it the case ?
that's not what I see happening here. I see very simply that the B.id_
column is a SERIAL so is linked to a sequence, however you are inserting
a row with a hardcoded "1" for a primary key; so the second B object,
which relies on the sequence, fails due to an identity conflict.
So let's repair the test case first, and that first B.id we'll set to
"10" so that it doesn't conflict.
Now we get the error you probably intended to send:
SELECT "Rel".id_a AS "Rel_id_a", "Rel".id_b AS "Rel_id_b",
"Rel".rel_data AS "Rel_rel_data"
FROM "Rel"
WHERE "Rel".id_a = %(param_1)s AND "Rel".id_b = %(param_2)s
2015-04-14 11:05:11,850 INFO sqlalchemy.engine.base.Engine {'param_1':
800, 'param_2': symbol('NEVER_SET')}
where this is, the merge() is proceeding to attempt to locate the object
by primary key but the PK is not filled in. This is the expected
behavior. The primary key of an object is never auto-populated until
it is flushed. So here, if you are passing in a transient object, you
need to set the PK yourself:
second_b = B(data='foooo')
session.add(second_b)
session.flush()
x = session.merge(Rel(id_a=800, rel_data="second", id_b=second_b.id_))
|fromsqlalchemy importcreate_engine fromsqlalchemy.orm
importsessionmaker engine
=create_engine("postgresql+psycopg2://psql_admin:psql_admin@localhost/fm")fromsqlalchemy.ext.declarative
importdeclarative_base Base=declarative_base()fromsqlalchemy
importInteger,ForeignKey,VARCHAR,TEXT,Boolean,DateTimefromsqlalchemy.orm
importrelationship fromsqlalchemy.sql.schema
importColumnclassB(Base):__tablename__='B'id_=Column(Integer,primary_key=True)data
=Column(VARCHAR(30))classRel(Base):__tablename__='Rel'id_a=Column(Integer,primary_key=True)id_b=Column(Integer,ForeignKey('B.id_'),primary_key=True)b
=relationship(B)rel_data=Column(VARCHAR(30))Session=sessionmaker(bind=engine)session
=Session()Base.metadata.create_all(engine,checkfirst=True)first_b=B(id_=1,data='ololo')session.add(first_b)session.commit()session.add(Rel(id_a=800,id_b=1,rel_data='first
relation
data'))second_b=B(data='foooo')session.add(second_b)x=session.merge(Rel(id_a=800,rel_data="second",b=second_b))session.commit()|
Here I have an error
IntegrityError: (raised as a result of Query-invoked autoflush;
consider using a session.no_autoflush block if this flush is
occuring prematurely) (IntegrityError) duplicate key value
violates unique constraint "B_pkey" DETAIL: Key (id_)=(1) already
exists. 'INSERT INTO "B" (data) VALUES (%(data)s) RETURNING
"B".id_' {'data': 'foooo'}
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