扩充 Flask-SqlAlchemy 声明性基础

Question

I tried the following, and it seems to work:

class BaseModel(db.Model):
    __abstract__ = True

    row_ver = db.Column(db.Integer, nullable=False)

    @declared_attr
    def __mapper_args__(cls):
        return {'version_id_col': cls.row_ver}

    def to_dict(self):
        res = dict()
        for c in self.__table__.columns:
            value = getattr(self, c.name)
            if isinstance(value, date):
                res[c.name] = value.isoformat()
            elif isinstance(value, uuid.UUID):
                res[c.name] = str(value)
            else:
                res[c.name] = value
        return res

class Account(BaseModel):
    __tablename__ = 'account'

    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String(100), nullable=False)

I'm not sure whether it is a proper way of augmenting the declarative base class, that is db.Model class. Is there anything wrong with the above code?

Also related: Is it possible to create custom declarative base by inheriting from db.Model (which itself is declarative base), something like below:

class Base(db.Model):
    #some code here

from sqlalchemy.ext.declarative import declarative_base 
BaseModel = declarative_base(cls=Base)

class Account(BaseModel)
    #...

Answer 1

To customize db.Model , declare a superclass of flask_sqlalchemy.Model and pass it to model_class as shown below.

from flask_sqlalchemy import Model, SQLAlchemy


class AppModel(Model):
    row_ver = db.Column(db.Integer, nullable=False)


db = SQLAlchemy(model_class=AppModel)


class Account(db.Model):
    pass


class Thing(db.Model):
    pass

Note that Account and Thing inherit from db.Model , not AppModel .