sqlalchemy_continuum_m2m_bug.py

import sqlalchemy
from sqlalchemy_continuum import make_versioned, version_class
from flask import Flask
from flask_sqlalchemy import SQLAlchemy

app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:////tmp/test.db'
db = SQLAlchemy(app)

make_versioned(
    user_cls=None,
)

class Person(db.Model):
    __versioned__ = {}

    id = db.Column(db.Integer, primary_key=True)

# We need to manually define a join table for m2m relations
billowers = db.Table(
    "billowers",
    db.Column("bill_id", db.Integer, db.ForeignKey("bill.id"), primary_key=True),
    db.Column("person_id", db.Integer, db.ForeignKey("person.id"), primary_key=True),
)

class Bill(db.Model):
    __versioned__ = {}
    id = db.Column(db.Integer, primary_key=True)

    people = db.relationship(Person, secondary=billowers)
    amount = db.Column(db.Float)

sqlalchemy.orm.configure_mappers()

PersonVersion = version_class(Person)
BillVersion = version_class(Bill)

db.drop_all()
db.create_all()

u1 = Person()
u2 = Person()

db.session.add(u1)
db.session.add(u2)
db.session.commit()

b1 = Bill(people=[u2], amount=10,)
b2 = Bill(people=[u2], amount=11,)

db.session.add(b1)

# Doing commit() here instead of after the next line causes the bug
db.session.commit()

db.session.add(b2)
db.session.commit()

# Change just the amount
b1.amount = 5
db.session.commit()


# The bug occurs in the last element of versions, where people is [],
# even though it's unchanged
versions = BillVersion.query.all()
for version in versions:
    assert version.people != []