title: SQLalchemy - Many to Many - Permitting Duplicate
body: <p>I've have the below many to many setup which works as expected. I can have an many Access_Paths with many Datasets between them. However I would like there to duplicate instances of a Dataset in Access_Path. Currently any attempt to add multiple instances results in just the one.</p>
  <pre><code>class Association(Base):
     __tablename__ = 'link_dataset_url'
     __table_args__ = {'autoload': True}
     dataset = Column('dataset_id', ForeignKey('dataset_attributes.id'), primary_key=False)
     accesspath = Column('access_path_id', ForeignKey('access_path.id'), primary_key=False)
  
  class Dataset(Base):
     __tablename__ = 'dataset'
     __table_args__ = {'autoload': True}
     access_path = relationship(&quot;Access_Path&quot;, secondary='link_dataset_url')
  
  class Access_Path(Base):
     __tablename__ = 'access_path'
     __table_args__ = {'autoload': True}
     datasets = relationship(&quot;Dataset&quot;, secondary='link_dataset_url')
  </code></pre>