models for graphene sqlalchemy example

models.py

from sqlalchemy import Column, Integer, ForeignKey
from sqlalchemy.orm import relationship
from database import Base

class PersonModel(Base):
    __tablename__ = 'person'
    uuid = Column(Integer, primary_key=True)
    Articles = relationship("ArticleModel")
    
class ArticleModel(Base):
    __tablename__ = 'article'
    uuid = Column(Integer, primary_key=True)
    person_id = Column(ForeignKey("person.uuid"))
    
Base.prepare(engine)
    

engine is not defined in this snippet, did you intend to import engine as well from database.py on line 3 ?