對於我的自引用表查詢，它無法將集合與對象或集合進行比較；

Question

class Place(db.Model):
    __tablename__ = 'places'
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String)

    lat = db.Column(db.FLOAT, default=None)
    long = db.Column(db.FLOAT, default=None)


    parent_place_id = db.Column(db.Integer, db.ForeignKey('places.id'))
    parent_place = db.relationship("Place")

    branches = db.relationship("Branch", back_populates="place")


    def __str__(self):
        return self.name

當我嘗試執行以下操作時：

p_place = models.Place.query.get(parent_place_id) if parent_place_id else None 
places = models.Place.query.filter(models.Place.parent_place==p_place ).all()

我收到以下錯誤：

Traceback (most recent call last):
  ...

  File "./app/ecom_chatbot/ecom_conversation.py", line 127, in show_locations
    places = models.Place.query.filter(models.Place.parent_place==p_place ).all()
  File "/root/ecom/ecom_bot/local/lib/python2.7/site-packages/sqlalchemy/sql/operators.py", line 304, in __eq__
    return self.operate(eq, other)
  File "/root/ecom/ecom_bot/local/lib/python2.7/site-packages/sqlalchemy/orm/attributes.py", line 175, in operate
    return op(self.comparator, *other, **kwargs)
  File "/root/ecom/ecom_bot/local/lib/python2.7/site-packages/sqlalchemy/orm/relationships.py", line 1037, in __eq__
    "Can't compare a collection to an object or collection; "
sqlalchemy.exc.InvalidRequestError: Can't compare a collection to an object or collection; use contains() to test for membership.

Answer 1

您的parent_place關系錯誤。 您需要的是many-to-one關系。

請參閱鄰接表關系

這里的Relationship（）配置與“正常”一對多關系的工作方式相同，不同之處在於“方向”（即關系是一對多還是多對一）是默認情況下假定為一對多。 為了建立多對一的關系，添加了一個額外的指令，稱為remote_side，它是Column或Column對象的集合，指示應被視為“遠程”的對象：

您應該這樣聲明您的parent_place關系：

parent_place = db.relationship("Place", remote_side=[id])

在上面的地方，將id列用作父關系（）的remote_side，從而將parent_id建立為“本地”端，然后該關系表現為多對一。