How to use the pypistats.extensions.db function in pypistats

def save(self, commit=True):
        """Save the record."""
        db.session.add(self)
        if commit:
            db.session.commit()
        return self

return commit and self.save() or self

    def save(self, commit=True):
        """Save the record."""
        db.session.add(self)
        if commit:
            db.session.commit()
        return self

    def delete(self, commit=True):
        """Remove the record from the database."""
        db.session.delete(self)
        return commit and db.session.commit()


class Model(CRUDMixin, db.Model):
    """Base model class that includes CRUD convenience methods."""

    __abstract__ = True


class SurrogatePK(object):
    """A mixin that adds a surrogate integer "primary key" column.

    Adds a surrogate integer "primary key" column named ``id`` to any
    declarative-mapped class.
    """

    __table_args__ = {"extend_existing": True}

    id = Column(db.Integer, primary_key=True)

"""Package stats tables."""
from pypistats.database import Column
from pypistats.database import Model
from pypistats.extensions import db


class OverallDownloadCount(Model):
    """Overall download counts."""

    __tablename__ = "overall"

    date = Column(db.Date, primary_key=True, nullable=False)
    package = Column(
        db.String(128), primary_key=True, nullable=False, index=True
    )
    # with_mirrors or without_mirrors
    category = Column(db.String(16), primary_key=True, nullable=False)
    downloads = Column(db.Integer(), nullable=False)

    def __repr__(self):
        return "

def register_extensions(app):
    """Register Flask extensions."""
    db.init_app(app)
    github.init_app(app)
    migrate.init_app(app, db)

def before_request():
    """Execute before requests."""
    g.user = None
    if "user_id" in session:
        g.user = User.query.get(session["user_id"])
    if "db" not in g:
        g.db = db

"""Database classes and models."""
from pypistats.extensions import db


Column = db.Column
basestring = (str, bytes)


class CRUDMixin(object):
    """Mixin that adds convenience methods for CRUD operations."""

    @classmethod
    def create(cls, **kwargs):
        """Create a new record and save it the database."""
        instance = cls(**kwargs)
        return instance.save()

    def update(self, commit=True, **kwargs):
        """Update specific fields of a record."""
        for attr, value in kwargs.items():
            setattr(self, attr, value)