db.py

def get_db():
    ctx = _app_ctx_stack.top
    con = getattr(ctx, "sa_database", None)
    if con is None:
        con = SQLAlchemy(ctx.app)
        ctx.sa_database = con
    return con

models.py

from .db import get_db
db = get_db()


class User(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    username = db.Column(db.String(80), unique=True)
    email = db.Column(db.String(120), unique=True)

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

run.py

def register_blueprints(app):
    from .models import User

    from .views import admin
    app.register_blueprint(admin)

views.py

from flask import Blueprint
from ..models import User
from ..db import get_db
# from werkzeug.local import LocalProxy

admin = Blueprint("admin", __name__, url_prefix="/admin")

db = LocalProxy(get_db)
# db = get_db()


@admin.route("/")
def index():
    # db = get_db()
    u1 = User(username="Piotr", email="ex@example.org")
    db.session.add(u1)
    db.session.commit()
    return "It Works!"