Using external transactions within test suite - flask-sqlalchemy

Question

External transactions.
I want to commit a model or models to the database and roll them back after each test. The pure sqlalchemy implementation (at the bottom) works the way I expect. However, the flask-sqlalchemy implementation fails to rollback the committed models after each test.
How can I bind flask-sqlalchemy's scoped session to the engine's connection?
Generic flask app:
from flask import Flask
from flask_sqlalchemy import SQLAlchemy
app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite://'
db = SQLAlchemy(app)
class A(db.Model):
id = db.Column(db.Integer, primary_key=True)
flask-sqlalchemy testcase (doesn't roll back):
from app import *
from unittest import TestCase
class Test(TestCase):
def setUp(self):
self.connection = db.engine.connect()
self.transaction = self.connection.begin()
options = dict(bind=self.connection, binds={})
self.session = db.create_scoped_session(options=options)
db.session = self.session
self.addCleanup(self.cleanup)
def cleanup(self):
self.transaction.rollback()
self.connection.close()
self.session.remove()
#classmethod
def setUpClass(cls):
db.create_all()
#classmethod
def tearDownClass(cls):
pass
def test_1(self):
a = A()
db.session.add(a)
db.session.commit()
assert len(db.session.query(A).all()) == 1
def test_2(self):
assert len(db.session.query(A).all()) == 0 # len is 1
sqlalchemy testcase (works):
from sqlalchemy import *
from sqlalchemy.orm import *
from sqlalchemy.ext.declarative import declarative_base
from unittest import TestCase
Base = declarative_base()
class A(Base):
__tablename__ = 'test'
id = Column(Integer, primary_key=True)
class Test(TestCase):
def setUp(self):
self.connection = e.connect()
self.transaction = self.connection.begin()
# Begin scoped session
factory = sessionmaker(bind=self.connection)
self.session = scoped_session(factory)
self.addCleanup(self.cleanup)
def cleanup(self):
self.session.close()
self.transaction.rollback()
self.connection.close()
#classmethod
def setUpClass(cls):
global e
e = create_engine("sqlite://")
Base.metadata.create_all(e)
#classmethod
def tearDownClass(cls):
pass
def test_1(self):
a = A()
self.session.add(a)
self.session.commit()
assert len(self.session.query(A).all()) == 1
def test_2(self):
assert len(self.session.query(A).all()) == 0

Answer 1

I had the same problem and perhaps my fix is the same as yours.
The this is now my setUp and tearDown:
import unittest
from my_app import db
class Test(unittest.TestCase):
def setUp(self):
self.connection = db.engine.connect()
self.trans = self.connection.begin()
db.session.configure(bind=self.connection, binds={})
def tearDown(self):
self.trans.rollback()
self.connection.close()
db.session.remove()
What actually did it for me was adding the:
binds={}
I haven't really investigated why this fixes it but it did for me. Would love to hear if anyone knows why the empty dict to bind fixes the problem.