I'm not sure whether this a bug or not:
When a mapped object has a foreign key reference to another object as
part of its own primary key, setting that column's value via a
relationship property causes session.merge() to not SELECT the object
first and thus encounter an IntegrityError when it tries to INSERT the
object.
I have written a reduction of this problem. When run as a script, the
second and later invocations will die with an IntegrityError.
"""
#!/usr/bin/env python
from sqlalchemy import Column, Unicode, Integer, ForeignKey,
create_engine
from sqlalchemy.orm import sessionmaker, relationship
from sqlalchemy.orm.exc import NoResultFound
from sqlalchemy.ext.declarative import declarative_base
Base = declarative_base()
class Alpha(Base):
__tablename__ = 'alpha'
id = Column(Integer, primary_key=True, nullable=False)
val = Column(Unicode, nullable=False)
def __init__(self, val):
self.val = val
class Foo(Base):
__tablename__ = 'foo'
alpha_id = Column(Integer, ForeignKey('alpha.id'),
primary_key=True, nullable=False)
alpha = relationship(Alpha)
foo_key = Column(Unicode, primary_key=True, nullable=False)
foo_val = Column(Integer, nullable=False)
def __init__(self, alpha, foo_key, foo_val):
self.alpha = alpha
self.foo_key = foo_key
self.foo_val = foo_val
engine = create_engine('sqlite:///regr-test.db', echo=True)
metadata = Base.metadata
metadata.create_all(engine)
Session = sessionmaker(bind=engine)
session = Session()
try:
a = session.query(Alpha).one()
except NoResultFound:
a = Alpha(u'blah')
session.add(a)
session.commit()
f = Foo(a, u'mykey', 99)
merged_f = session.merge(f)
session.add(merged_f)
session.commit()
"""
What makes me think this might be a bug is that the script suddenly
starts working as intended if Foo.__init__ is modified to set
"self.alpha_id = alpha.id" instead of "self.alpha = alpha".
Is this a bug, or is there some aspect of using a relationship to
implicitly set self.alpha_id that I'm not understanding?
--
Erik Swanson
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