Flask SQLAlchemy verlängert Beziehungsmodell von Plan Basismodell

Question

ich ein User-Modell auf dem Haupt models.py und das Post-Modell auf meinem Blog Plan habe. Ich möchte einen Basis-BlogUser erstellen, der den ForeignKey enthält, und ich kann das Benutzermodell in der Hauptanwendung erweitern, um die Eins-zu-viele-Beziehung zwischen den Benutzer- und Postmodellen zu erstellen. Unten ist der Code.

app/models.py

from app import db 
from flask_login import UserMixin 
from flask_bcrypt import generate_password_hash 
from app.blueprints.blog.models import BlogUser 

class User(BlogUser, UserMixin): 
    id = db.Column(db.Integer, primary_key=True) 
    username = db.Column(db.String(32), unique=True, nullable=False) 
    email = db.Column(db.String(250), unique=True, nullable=False) 
    password = db.Column(db.String(32), nullable=False) 
    is_admin = db.Column(db.Boolean, default=False) 

    def __init__(self, username, email, password, is_admin): 
     self.username = username 
     self.email = email 
     self.password = generate_password_hash(password) 
     self.is_admin = is_admin 

    def __repr__(self): 
     return '<User %r>' % self.username 

app/Pläne/Blog/models.py

from app import db 
from datetime import datetime 

class BlogUser(db.Model): 
    __abstract__ = True 
    posts = db.relationship('Post', backref='author', lazy='dynamic') 

class Post(db.Model): 
    id = db.Column(db.Integer, primary_key=True) 
    title = db.Column(db.String(80), nullable=False) 
    body = db.Column(db.Text, default='') 
    pub_date = db.Column(db.DateTime) 
    user_id = db.Column(db.Integer, db.ForeignKey('user.id')) 

    def __init__(self, title, body, author, pub_date=None): 
     self.title = title 
     self.body = body 
     if pub_date is None: 
      pub_date = datetime.utcnow() 
     self.pub_date = pub_date 
     self.author = author 

    def __repr__(self): 
     return '<Post %r>' % self.title 

Dies ist der Fehler, den ich bekommen:

Traceback (most recent call last): 
    File "C:/Users/vsantiago/Desktop/flask app template/application.py", line 1, in <module> 
    from app import app as application 
    File "C:\Users\vsantiago\Desktop\flask app template\app\__init__.py", line 18, in <module> 
    from app import views 
    File "C:\Users\vsantiago\Desktop\flask app template\app\views.py", line 6, in <module> 
    from app.models import User 
    File "C:\Users\vsantiago\Desktop\flask app template\app\models.py", line 6, in <module> 
    class User(BlogUser, UserMixin): 
    File "C:\pyenv\featurerequest\lib\site-packages\flask_sqlalchemy\__init__.py", line 602, in __init__ 
    DeclarativeMeta.__init__(self, name, bases, d) 
    File "C:\pyenv\featurerequest\lib\site-packages\sqlalchemy\ext\declarative\api.py", line 64, in __init__ 
    _as_declarative(cls, classname, cls.__dict__) 
    File "C:\pyenv\featurerequest\lib\site-packages\sqlalchemy\ext\declarative\base.py", line 88, in _as_declarative 
    _MapperConfig.setup_mapping(cls, classname, dict_) 
    File "C:\pyenv\featurerequest\lib\site-packages\sqlalchemy\ext\declarative\base.py", line 103, in setup_mapping 
    cfg_cls(cls_, classname, dict_) 
    File "C:\pyenv\featurerequest\lib\site-packages\sqlalchemy\ext\declarative\base.py", line 123, in __init__ 
    self._scan_attributes() 
    File "C:\pyenv\featurerequest\lib\site-packages\sqlalchemy\ext\declarative\base.py", line 216, in _scan_attributes 
    "Mapper properties (i.e. deferred," 
sqlalchemy.exc.InvalidRequestError: Mapper properties (i.e. deferred,column_property(), relationship(), etc.) must be declared as @declared_attr callables on declarative mixin classes. 

Answer 1

Ziemlich viel wie die Fehlerzustände bewegen das direkte relationship Attribut zu einem @declared_attr verzierten aufrufbaren in BlogUser abs Trakt-Basisklasse:

from sqlalchemy.ext.declarative import declared_attr 


class BlogUser(db.Model): 
    __abstract__ = True 

    @declared_attr 
    def posts(cls): 
     return db.relationship('Post', backref='author', lazy='dynamic')