Something a bit more normal now.
Combining optimistic concurrency control with cascading PK updates is
problematic, if you load the child relation, the session issues
unecessary updates for the children, resulting in
ConcurrentModificationError
"""
import sqlalchemy as sql
from sqlalchemy import orm
from sqlalchemy.ext.declarative import declarative_base
__metaclass__ = type
engine = sql.create_engine("postgresql:///avdd")
metadata = sql.MetaData(bind=engine)
db = orm.create_session(bind=engine, autocommit=False)
T = declarative_base(metadata=metadata)
class P(T):
__tablename__ = 'p'
id = sql.Column(sql.String, primary_key=True)
version = sql.Column(sql.Integer, nullable=False, default=1)
cc = orm.relation('C', backref='parent', passive_updates=True)
__mapper_args__ = {'version_id_col': version}
class C(T):
__tablename__ = 'c'
i = sql.Column(sql.String, primary_key=True)
p = sql.Column(sql.String,
sql.ForeignKey('p.id', onupdate='cascade',
ondelete='cascade'),
primary_key=True)
version = sql.Column(sql.Integer, nullable=False, default=1)
__mapper_args__ = {'version_id_col': version}
metadata.create_all()
P.__table__.delete().execute()
with db.transaction:
p = P(id='P1', cc=[C(i='C.1'), C(i='C.2')])
db.add(p)
db.expunge_all()
p = db.query(P).first()
with db.transaction:
p.id = 'P2'
# ok, no ConcModError
db.expunge_all()
p = db.query(P).first()
with db.transaction:
p.id = 'P3'
p.cc
# issues spurious updates, throws ConcModError
"""
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