Factory boy to select from existing flask_sqlalchemy table with Iterator using parameter

There are lots of great answers here, but I can’t quite find the one to solve my problem.

Two SQLAlchemy models: Calendar and Transaction. Transactions link to the Calendar model:

class Calendar(Model):
    calendar_id = db.Column(db.Integer, primary_key=True, autoincrement=True)
    cal_date = db.Column(db.Date, unique=True, nullable=False)

class Transactions(Model):
    transaction_id = db.Column(db.Integer, primary_key=True, autoincrement=True)
    transaction_date = Column(db.Date, nullable=False)
    transaction_calendar_id = reference_col('calendar', pk_name='calendar_id')
    transaction_calendar = relationship('Calendar', backref=db.backref('transaction_dates'))

Then Factory Boy classes to generate SQLAlchemy objects:

class CalendarFactory(BaseFactory):
    calendar_id = Sequence(lambda n: n)
    cal_date = Sequence(lambda n: datetime.date(2021,1,1) + relativedelta(days=n))

    class Meta:
        model = Calendar
        sqlalchemy_get_or_create = ('cal_date', )
        
class TransactionFactory(BaseFactory):
    transaction_date = Sequence(lambda n: datetime.date(2022,1,1) + relativedelta(days=n))
    transaction_calendar = SubFactory(CalendarFactory, cal_date=SelfAttribute('..transaction_date'))

    class Meta:
        model = Transactions

The trouble I’m having is that when my TransactionFactory is generated, it tries to generate a CalendarFactory object even when there is already one for the given date, and I get the following error:

(sqlite3.IntegrityError) UNIQUE constraint failed: calendar.cal_date

I’ve tried a number of strategies including StaticFactory as describe in Avoiding duplicates with factory_boy factories

The solution I’m trying to work on now is described in Choosing from a populated table in factory boy while using flask

This is what I’m trying, but it ain’t working:

def lazy_calendar(cal_date):
  """Turn query into a lazily evaluated generator"""
  yield from Calendar.query.filter_by(cal_date=cal_date).all()

class TransactionFactory(BaseFactory):
    transaction_date = Sequence(lambda n: datetime.date(2022,1,1) + relativedelta(days=n))
    transaction_calendar = LazyAttribute(lambda c: lazy_calendar(c.transaction_date))

Question: can I call a Factory Boy Iterator with a parameter so I can get back the generator with the single date that I want?

Or am I completely barking up the wrong tree here?

Note: this issue has only come to light when I’m running unit tests simulatenously via VS Code Testing feature. When I run my tests sequentially via pytest, it’s fine. But I would like to get the multithreaded version working if poss.