title: SQLAlchemy relationships: more than one self-referenced columns
body: <p>There is an sqlalchemy object</p>
  
  <pre><code>class Employee(Base):
      __tablename__ = "employee"
      # Columns
      id = Column(Integer, primary_key=True, autoincrement=True)
      representative_id = Column(Integer, ForeignKey('employee.id'))
      parent_id = Column(Integer, ForeignKey('employee.id'))
      affiliate_id = Column(Integer, ForeignKey('employee.id'))
  
      # Relatonships
      representative = relationship("Employee", ????)
      parent = relationship("Employee", ????)
      affiliate = relationship("Employee", ????)
  </code></pre>
  
  <p>How to configure the relationships in the right way if an employee can have, 0 or 1 parent, affiliate and representative? Do know these three are different ones. DB - MySQL</p>