How to implement Foreign Key in sqlmodel in fastapi

models.py

from typing import Optional
from sqlmodel import Field, Relationship, Session, SQLModel, create_engine, select, Column, VARCHAR

class User(SQLModel, table=True):
    __tablename__ = 'users'
    
    user_id: Optional[int] = Field(default=None, primary_key=True)
    first_name : str = Field(sa_column=Column("first_name", VARCHAR(54),nullable=False))
    last_name : str = Field(sa_column=Column("last_name", VARCHAR(54), nullable=True))
    email : str = Field(sa_column=Column("email", VARCHAR(54), unique=True, nullable=False))
    password : str = Field(sa_column=Column("password", VARCHAR(256), nullable=False))
    #role_id should be added as foreign key here

class Role(SQLModel, table=True):
    __tablename__ = 'roles'

    role_id: Optional[int] = Field(default=None, primary_key=True)
    name : str = Field(sa_column=Column("name", VARCHAR(54),nullable=False))
    

I have two models User and Role, here I want to add role_id as foreign key in User table. How can I achieve it in sqlmodel in fastapi