I'm back with another SQL Alchemy question..

So I have a many-to-many relationship between two classes: Dataset and Column (ignore the obvious horrible names).

I was using an association table before and everything was working great. But I now need to add an extra column to that association table so I had to convert the table to an object.

I'm following the docs but I keep getting this error:

AssertionError: Attribute 'datasets' on class '<class 'test_models.Table'>' doesn't handle objects of type '<class 'test_models.Dataset'>'

My Setup

class Dataset(BASE):
 __tablename__ = 'dataset'

 dataset_id = Column(INTEGER(10), primary_key=True, unique=True, nullable=False)
 dataset_name = Column(Text, nullable=False)
 dataset_title = Column(Text)
 dataset_comment = Column(Text)

 tables = relationship('Dataset_Table',
 back_populates='datasets')


class Table(BASE):
 __tablename__ = 'table'

 table_id = Column(INTEGER(11), primary_key=True, unique=True, nullable=False)

 table_name = Column(Text, nullable=False)
 table_group = Column(Text)
 table_description = Column(Text)

 table_longitudinal = Column(Enum('S', 'Y', 'N', 'L'))

 datasets = relationship('Dataset_Table',
 back_populates='tables')

Here's is a link to the full stack trace: https://pastebin.com/NHgLCWq6

Is my approach incorrect? What am I doing wrong? I simply want my many-to-many to work with the associative table as before with the Association Table but with an Association Object

EDIT:

I apologize, I didn't include the association table linking the two tables above together:

class Dataset_Table(BASE):
 __tablename__ = 'dataset_table'

 id = Column('id', INTEGER, primary_key=True, unique=True, nullable=False)
 dataset_id = Column('dataset_id', INTEGER, ForeignKey('dataset.dataset_id'), nullable=False)
 table_id = Column('table_id', INTEGER, ForeignKey('table.table_id'), nullable=False)

 position = Column(INTEGER, nullable=False)

datasets = relationship('Dataset',
 back_populates='tables')

tables = relationship('Table',
 back_populates='datasets')

As you can see, this is a standard many-to-many with back population like this

Im putting the full stack trace below:

 Traceback (most recent call last):
 File "/Users/kevin.dasilva/SQL_tings/SQL_ingest.py", line 103, in <module>
 sess.add_all(objs)
 File "/Users/kevin.dasilva/SQL_tings/SQL_env/lib/python3.6/site- 
packages/sqlalchemy/orm/session.py", line 1785, in add_all
 self.add(instance, _warn=False)
 File "/Users/kevin.dasilva/SQL_tings/SQL_env/lib/python3.6/site- 
packages/sqlalchemy/orm/session.py", line 1776, in add
 self._save_or_update_state(state)
 File "/Users/kevin.dasilva/SQL_tings/SQL_env/lib/python3.6/site- 
packages/sqlalchemy/orm/session.py", line 1795, in 
_save_or_update_state
halt_on=self._contains_state):
 File "/Users/kevin.dasilva/SQL_tings/SQL_env/lib/python3.6/site- 
packages/sqlalchemy/orm/mapper.py", line 2870, in cascade_iterator
visited_states, halt_on))
 File "/Users/kevin.dasilva/SQL_tings/SQL_env/lib/python3.6/site- 
packages/sqlalchemy/orm/relationships.py", line 1591, in 
 cascade_iterator
c.__class__
 AssertionError: Attribute 'datasets' on class '<class 
 'test_models.Table'>' doesn't handle objects of type '<class 
 'test_models.Dataset'>'

EDIT:

I believe I am searching for a "bidirectional many to many" with an association object