gistfile1.py

class Entry(Base):
    __tablename__ = 'entries'
    id = Column(Integer, primary_key=True)
    text = Column(String(200))
    created_at = Column(DateTime, default=datetime.now, nullable=False)

    comments = relationship('Comment', backref="entry") # Commentテーブルへのリレーション

class Comment(Base):
    __tablename__ = 'comments'
    id = Column(Integer, primary_key=True)
    entry_id = Column(Integer, ForeignKey('entries.id'), nullable=False) # ForeingKey
    text = Column(String(200))
    created_at = Column(DateTime, default=datetime.now, nullable=False)

entry = Entry.query.get(1)
entry.comments[0] # => <__main__.Comment object at 0x10184acd0>

comment = Comment.query.get(1)
comment.entry # => <__main__.Entry object at 0x101841a10> backref設定する事で逆参照できる