Python Can'；在SQLAlchemy flask中的结果对象上设置属性

我在Flask SQLAlchemy中遇到问题，我可以设置place_集合中对象的属性，但当我想为places中的对象设置属性时，出现了一个错误：

Traceback (most recent call last):
  File "/Users/user/PycharmProjects/website/venv/lib/python3.6/site-packages/flask/app.py", line 2309, in __call__
    return self.wsgi_app(environ, start_response)
  File "/Users/user/PycharmProjects/website/venv/lib/python3.6/site-packages/werkzeug/contrib/fixers.py", line 152, in __call__
    return self.app(environ, start_response)
  File "/Users/user/PycharmProjects/website/venv/lib/python3.6/site-packages/flask/app.py", line 2295, in wsgi_app
    response = self.handle_exception(e)
  File "/Users/user/PycharmProjects/website/venv/lib/python3.6/site-packages/flask/app.py", line 1741, in handle_exception
    reraise(exc_type, exc_value, tb)
  File "/Users/user/PycharmProjects/website/venv/lib/python3.6/site-packages/flask/_compat.py", line 35, in reraise
    raise value
  File "/Users/user/PycharmProjects/website/venv/lib/python3.6/site-packages/flask/app.py", line 2292, in wsgi_app
    response = self.full_dispatch_request()
  File "/Users/user/PycharmProjects/website/venv/lib/python3.6/site-packages/flask/app.py", line 1815, in full_dispatch_request
    rv = self.handle_user_exception(e)
  File "/Users/user/PycharmProjects/website/venv/lib/python3.6/site-packages/flask/app.py", line 1718, in handle_user_exception
    reraise(exc_type, exc_value, tb)
  File "/Users/user/PycharmProjects/website/venv/lib/python3.6/site-packages/flask/_compat.py", line 35, in reraise
    raise value
  File "/Users/user/PycharmProjects/website/venv/lib/python3.6/site-packages/flask/app.py", line 1813, in full_dispatch_request
    rv = self.dispatch_request()
  File "/Users/user/PycharmProjects/website/venv/lib/python3.6/site-packages/flask/app.py", line 1799, in dispatch_request
    return self.view_functions[rule.endpoint](**req.view_args)
  File "/Users/user/Document/Python/Test/Code/app/main/views.py", line 108, in index
    place.distance = round(distance_computing, 1)
AttributeError: can't set attribute

如何设置join search对象的属性，有人可以帮助我吗

place_collections = Place.query.filter_by(county='BKK')

places = db.session.query(Place.roll_number, Place.name, Place.website, Place.address, Place.distance)
            .outerjoin(Rank, Rank.place_id == Place.place_id)

它们都是类“flask\u sqlalchemy.BaseQuery”类型

---

---

型号

class Rank(db.Model):
    __tablename__ = 'rank'
    place_id = db.Column(db.String(50))
    name = db.Column(db.String(255), nullable=False, primary_key=True)
    rank = db.Column(db.Integer)

class Place(db.Model):
    _tablename_ = 'school'
    place_id = db.Column(db.String(50), primary_key=True)
    roll_number = db.Column(db.String(50))
    name = db.Column(db.String(255), nullable=False)
    address = db.Column(db.String(255))
    distance = db.Column(db.String(50))
    rank = db.relationship('Rank',backref=db.backref('roll_number1'), lazy=True, uselist=False)

---

place\u collections=place.query.filter\u by（county='BKK'）

将返回

place

对象的集合。这类似于普通炼金术中的session.query（Place）.filter_by（county='BKK'）

但是，从SQLAlchemy：

该查询还接受ORM插入指令的描述符作为参数。任何 时间多个类实体或基于列的实体表示为 对于query（）函数的参数，返回结果表示为 元组

关键点在于，当您指定要查询的特定列时（如此处所述）：

places = db.session.query(Place.roll_number, Place.name,
    Place.website, Place.address, Place.distance).\
    outerjoin(Rank, Rank.place_id == Place.place_id)

结果表示为

元组的集合

我的第一印象是，

无法设置属性

是一条奇怪的错误消息，试图将属性值分配给

元组

，因此我尝试了：

>>> t = tuple()
>>> t.attribute = 9
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'tuple' object has no attribute 'attribute'

因此，

sqlalchemy.util.\u collections.result

是一种

tuple

类型

如果我们尝试为一个属性分配一个值，该属性不是查询的列之一：

>>> a_result.newattribute = 'something'
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'result' object has no attribute 'newattribute'

这与您收到的错误消息相同

因此，

sqlalchemy.util.\u collections.result

对象支持列名的属性访问，但由于它是一个

元组，所以它仍然是不可变的，因此无法写入这些属性

要修复您的特定错误（除非出于某种原因您专门查询了这些列），请将您的
places
查询更改为：

places = db.session.query(Place).outerjoin(Rank, Rank.place_id == Place.place_id)

此错误的另一个可能原因（“AttributeError:无法设置属性”错误）是当列和属性的名称相同时

我碰巧有一个以前添加（忘记）的
@属性
，然后创建了一个同名列

>>> q = session.query(Racecard.id, Racecard.meeting)
>>> a_result = q[0]
>>> type(a_result)
<class 'sqlalchemy.util._collections.result'>

>>> issubclass(type(a_result), tuple)
True

>>> a_result.newattribute = 'something'
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'result' object has no attribute 'newattribute'

>>> from collections import namedtuple
>>> Racecard = namedtuple('Racecard', 'id, meeting')
>>> rc = Racecard(1, 'Doomben')
>>> rc.meeting = 'Eagle Farm'
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: can't set attribute

places = db.session.query(Place).outerjoin(Rank, Rank.place_id == Place.place_id)