[Python] Why are the ForeignKey constraints not working? [duplicate]

I have this model:

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

engine = create_engine('sqlite:///')
Session = sessionmaker(bind=engine)
sess = Session()
Base = declarative_base()

class Users(Base):
__tablename__ = 'mans'
id = Column(Integer, primary_key=True)
user_id = Column(Integer, ForeignKey("address.id"))
name = Column(String)
age = Column(Integer)

class Address(Base):
__tablename__ = 'address'
id = Column(Integer, primary_key=True)
email = Column(String)

Base.metadata.create_all(engine)

user1 = Users(id=1, user_id=2, name='Mike', age=21)
adr1 = Address(id=1, email='test@mail.ru')


sess.add(user1)
sess.add(adr1)

sess.commit()
x = sess.query(Users).filter(Users.id>0).first()

print(x.name)


I can't understand why it's working if I have ForeignKey constrains:

user_id = Column(Integer, ForeignKey("address.id"))


And on this line trying to access to nonexistent key:

user1 = Users(id=1, user_id=2, name='Mike', age=21)

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