Hi!
I recently came across some confusing behavior in relations and cascading
using sqllite, and I was hoping that I might get some help explaining what
the behavior is here. I put together a minimum failing script here. I'm
trying to commit one instance of each of two classes, but what ends up
happening is that I commit two copies of the many part of a one-to-many
relation. I suspect that this has something to do with cascading, but I
found a bug report for similar behavior
<http://www.agapow.net/programming/python/sqlalchemy-merge-and-relations/>that
claims to have been fixed several years ago, and I'm wondering if there was
some kind of regression? I'm running SQLAlchemy 1.3.1 on Ubuntu and I'm
still using sqllite at this stage of development.
from sqlalchemy import create_engine
from sqlalchemy.orm import scoped_session, sessionmaker
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import Column, Integer, String, Text, ForeignKey
from sqlalchemy.orm import relationship
import os
db_engine = create_engine('sqlite:///sample.db', convert_unicode=True)
db_session = scoped_session(sessionmaker(autocommit=False,
autoflush=False,
bind=db_engine))
Base = declarative_base()
Base.query = db_session.query_property()
class Head(Base):
__tablename__ = 'head'
id = Column(String, primary_key=True)
tassel_threads = relationship("TasselThread", back_populates="head")
def __init__(self, id):
self.id=id
class TasselThread(Base):
__tablename__ = 'tassel_thread'
id = Column(Integer, primary_key=True)
head_id = Column(Integer, ForeignKey('head.id'), nullable=False)
head = relationship("Head", back_populates="tassel_threads")
def __init__(self, head):
self.head = head
def init_db():
Base.metadata.create_all(bind=db_engine)
def do_db_work():
my_head = Head(id="foobar")
my_head = db_session.merge(my_head)
db_session.commit()
my_tassel_thread = TasselThread(head=my_head)
db_session.merge(my_tassel_thread)
db_session.commit()
if os.path.exists("sample_data.db"):
os.remove("sample_data.db")
init_db()
do_db_work()
a = db_session.query(TasselThread).all()
print(len(a))
# output: 2, should be 1
Thanks for any help you might be able to provide!
-Lyla Fischer
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http://www.sqlalchemy.org/
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