Flask & SqlAlchemy - alembic session.add_all() results in AttributeError: 'bool' object has no attribute 'clear' error

Question

I'm trying to insert some data as part of deployment. I've created following alembic revision script

revision = '59891ffc8502'
down_revision = '349540cf9cef'

from alembic import op
import sqlalchemy as sa
from sqlalchemy.dialects import mysql
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import sessionmaker, relationship

Session = sessionmaker()
Base = declarative_base()

class Colours(Base):
    __tablename__ = 'colours'

    id = sa.Column(sa.Integer, primary_key=True)
    name = sa.Column('name', sa.Unicode(length=25), nullable=False)
    code = sa.Column('code', sa.Unicode(length=2), nullable=False)


def upgrade():
    bind = op.get_bind()
    session = Session(bind=bind)
    session._model_changes = False

    op.alter_column('colours', 'code', new_column_name='code', existing_type=mysql.VARCHAR(length=25))

    col = [ 
            { "name": "Black", "code": "ff00cc" }, 
            { "name": "Blue", "code": "ff00cc" }, 
            { "name": "Brown", "code": "ff00cc" }, 
            { "name": "Gold", "code": "ff00cc" }, 
            { "name": "Green", "code": "ff00cc" }
    ]

    # populate colours table
    colours = { c['name']: Colours(name=unicode(c['name']), code=c['code']) for c in col}
    session.add_all(colours.values())

    session.commit()
    # ### end Alembic commands ###

and upgrade head results in AttributeError: 'bool' object has no attribute 'clear' error. Any clue?

Answer 1

Turns out, setting session._model_changes = False doesn't take care of Flask-SQLAlchemy enough. You need to completely unregister the event handlers it registers.

from flask_sqlalchemy import _SessionSignalEvents
from sqlalchemy import event
from sqlalchemy.orm import Session as BaseSession

Session = sessionmaker()

event.remove(BaseSession, 'before_commit', _SessionSignalEvents.session_signal_before_commit)
event.remove(BaseSession, 'after_commit', _SessionSignalEvents.session_signal_after_commit)
event.remove(BaseSession, 'after_rollback', _SessionSignalEvents.session_signal_after_rollback)