flask-PK-FK.py

from sqlalchemy import create_engine, Column, ForeignKey, Integer, String
from sqlalchemy.orm import relationship, Session
from sqlalchemy.ext.declarative import declarative_base

Base = declarative_base()
metadata = Base.metadata

class Parent(Base):
    __tablename__ = 'parent'
    id = Column(Integer, primary_key=True)
    name = Column(String, nullable=False, unique=True)

class Child(Base):
    __tablename__ = 'child'
    parent_id = Column(ForeignKey(Parent.id), primary_key=True)
    name = Column(String, nullable=False, unique=True)

    parent = relationship(Parent, backref='children')

engine = create_engine('sqlite://', echo=True)
session = Session(bind=engine)
metadata.bind = engine
metadata.create_all()

p = Parent(name='parent1')
c = Child(parent=p, name='child1')
session.add(p)
session.commit()