old_contents: from database import TableBase, Column, String, ForeignKey
  
  
  class Link(TableBase):
      __tablename__ = 'link'
      link_id = Column(String(256), primary_key=True)
      node_a_id = Column(String(256), ForeignKey('node.node_id'))
      node_b_id = Column(String(256), ForeignKey('node.node_id'))
      link_catalog = Column(String(256))
      link_name = Column(String(256))
  
new_contents: from database import TableBase, Column, String, ForeignKey
  
  
  class Link(TableBase):
      __tablename__ = 'link'
      link_id = Column(String(256))
      node_a_id = Column(String(256), ForeignKey('node.node_id'), primary_key=True)
      node_b_id = Column(String(256), ForeignKey('node.node_id'), primary_key=True)
      link_catalog = Column(String(256))
      link_name = Column(String(256))
  
subject: fix 'Link' primary key problem