склянка SQLAlchemy hybrid_property Логическое значение этого предложения не определено

Question

склянка SQLAlchemy hybrid_property Логическое значение этого предложения не определено

1

Я использую Python 3.6.5, Flask 1.0.2, SQLAlchemy 1.0.5, и я хочу определить атрибут как максимум между двумя другими, основанными на примере гибридного свойства flask-admin:

from flask import Flask
from flask_sqlalchemy import SQLAlchemy
from sqlalchemy.ext.hybrid import hybrid_property

import flask_admin as admin
from flask_admin.contrib import sqla

from sqlalchemy.sql.expression import func

# Create application
app = Flask(__name__)

# Create dummy secrey key so we can use sessions
app.config['SECRET_KEY'] = '123456790'

# Create in-memory database
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///sample_db_2.sqlite'
app.config['SQLALCHEMY_ECHO'] = True
db = SQLAlchemy(app)


# Flask views
@app.route('/')
def index():
    return '<a href="/admin/">Click me to get to Admin!</a>'


class Screen(db.Model):
    __tablename__ = 'screen'
    id = db.Column(db.Integer, primary_key=True)
    width = db.Column(db.Integer, nullable=False)
    height = db.Column(db.Integer, nullable=False)

    @hybrid_property
    def max(self):
        return max(self.height, self.width)

class ScreenAdmin(sqla.ModelView):
    """ Flask-admin can not automatically find a hybrid_property yet. You will
        need to manually define the column in list_view/filters/sorting/etc."""
    column_list = ['id', 'width', 'height', 'max']
    column_sortable_list = ['id', 'width', 'height', 'max']

    # Flask-admin can automatically detect the relevant filters for hybrid properties.
    column_filters = ('max', )


# Create admin
admin = admin.Admin(app, name='Example: SQLAlchemy2', template_mode='bootstrap3')
admin.add_view(ScreenAdmin(Screen, db.session))

if __name__ == '__main__':

    # Create DB
    db.create_all()

    # Start app
    app.run(debug=True)

Но он терпит неудачу, поднимая эту ошибку:

    raise TypeError("Boolean value of this clause is not defined")

Проследить:

/home/bibo/usr/miniconda/envs/otroflask/lib/python3.6/site-packages/flask_sqlalchemy/__init__.py:794: FSADeprecationWarning: SQLALCHEMY_TRACK_MODIFICATIONS adds significant overhead and will be disabled by default in the future.  Set it to True or False to suppress this warning.
  'SQLALCHEMY_TRACK_MODIFICATIONS adds significant overhead and '
Traceback (most recent call last):
  File "app.py", line 49, in <module>
    admin.add_view(ScreenAdmin(Screen, db.session))
  File "/home/bibo/usr/miniconda/envs/otroflask/lib/python3.6/site-packages/flask_admin/contrib/sqla/view.py", line 329, in __init__
    menu_icon_value=menu_icon_value)
  File "/home/bibo/usr/miniconda/envs/otroflask/lib/python3.6/site-packages/flask_admin/model/base.py", line 804, in __init__
    self._refresh_cache()
  File "/home/bibo/usr/miniconda/envs/otroflask/lib/python3.6/site-packages/flask_admin/model/base.py", line 881, in _refresh_cache
    self._list_columns = self.get_list_columns()
  File "/home/bibo/usr/miniconda/envs/otroflask/lib/python3.6/site-packages/flask_admin/model/base.py", line 1022, in get_list_columns
    excluded_columns=self.column_exclude_list,
  File "/home/bibo/usr/miniconda/envs/otroflask/lib/python3.6/site-packages/flask_admin/contrib/sqla/view.py", line 531, in get_column_names
    column, path = tools.get_field_with_path(self.model, c)
  File "/home/bibo/usr/miniconda/envs/otroflask/lib/python3.6/site-packages/flask_admin/contrib/sqla/tools.py", line 150, in get_field_with_path
    value = getattr(current_model, attribute)
  File "/home/bibo/usr/miniconda/envs/otroflask/lib/python3.6/site-packages/sqlalchemy/ext/hybrid.py", line 867, in __get__
    return self._expr_comparator(owner)
  File "/home/bibo/usr/miniconda/envs/otroflask/lib/python3.6/site-packages/sqlalchemy/ext/hybrid.py", line 1066, in expr_comparator
    owner, self.__name__, self, comparator(owner),
  File "/home/bibo/usr/miniconda/envs/otroflask/lib/python3.6/site-packages/sqlalchemy/ext/hybrid.py", line 1055, in _expr
    return ExprComparator(cls, expr(cls), self)
  File "app.py", line 34, in number_of_pixels
    return max(self.width,self.height)
  File "/home/bibo/usr/miniconda/envs/otroflask/lib/python3.6/site-packages/sqlalchemy/sql/elements.py", line 2975, in __bool__
    raise TypeError("Boolean value of this clause is not defined")

Я пробовал с максимальной функцией sqlalchemy:

return func.max(self.height, self.width)

Но он возвращает буквально функцию, а не значение.

Я также попытался использовать концепцию этого ответа без успеха.

brivadeneira 29 авг. 2018, в 06:28

Источник

Теги:

python

python-3.x

flask

flask-sqlalchemy

1 ответ

Ещё вопросы

Pyglouthon · Accepted Answer · 2018-09-11T11-45-00.000Z

Вы могли бы попробовать что-то вроде этого:

@hybrid_property
def max_size(self):
   return (
            db.session.query(func.max(Screen.height, Screen.width))
            .filter(Screen.id == self.id)
            .scalar()
        )

@max_size.expression
def max_size(cls):
    return (
            select([func.max(Screen.height, Screen.width)])
            .where(Screen.id == cls.id)
            .label("max_size")
        )