使用SqlAlchemy和PostgreSQL找不到外键

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

class Table1(Base):
    __tablename__ = 'table1'
    id = Column(Integer, primary_key=True)
    # ...

class Table2(Base):
    __tablename__ = 'table2'
    id = Column(Integer, primary_key=True)
    table1_id = Column(Integer, ForeignKey('table1.id'))
    table1 = relationship('Table1')
    # ...

from sqlalchemy import create_engine
from sqlalchemy.orm import sessionmaker

engine = create_engine('postgresql://username:password@localhost/dbname')
Session = sessionmaker(bind=engine)
session = Session()

Base.metadata.create_all(engine)