如何最好地在rails应用程序的DB中表示角色？

CREATE TABLE roles (
  id SERIAL PRIMARY KEY,
  name VARCHAR(255) NOT NULL UNIQUE
);

CREATE TABLE permissions (
  id SERIAL PRIMARY KEY,
  name VARCHAR(255) NOT NULL UNIQUE
);

CREATE TABLE role_permissions (
  role_id INT REFERENCES roles(id),
  permission_id INT REFERENCES permissions(id),
  PRIMARY KEY (role_id, permission_id)
);

CREATE TABLE users (
  id SERIAL PRIMARY KEY,
  name VARCHAR(255) NOT NULL
);

CREATE TABLE user_roles (
  user_id INT REFERENCES users(id),
  role_id INT REFERENCES roles(id),
  PRIMARY KEY (user_id, role_id)
);

class UsersController < ApplicationController
  before_action :check_permissions, only: [:edit, :update]

  def edit
    @user = User.find(params[:id])
  end

  def update
    @user = User.find(params[:id])
    # 更新用户逻辑
  end

  private

  def check_permissions
    unless current_user.admin? || current_user == @user
      redirect_to root_path, alert: "You don't have permission to do that."
    end
  end
end