如何在rails中建立多对多的关系

class CreateRolesUsersTable < ActiveRecord::Migration[6.0]
  def change
    create_table :roles_users, id: false do |t|
      t.belongs_to :role, index: true
      t.belongs_to :user, index: true
    end
  end
end

class User < ApplicationRecord
  has_many :roles_users
  has_many :roles, through: :roles_users

  def roles=(roles)
    self.roles_users = roles.map do |role|
      roles_users.create(role: role)
    end
  end
end

class Role < ApplicationRecord
  has_many :roles_users
  has_many :users, through: :roles_users

  def users=(users)
    self.roles_users = users.map do |user|
      roles_users.create(user: user)
    end
  end
end

class SessionsController < ApplicationController
  def create
    user = User.find_by(email: params[:email])
    if user && user.authenticate(params[:password])
      # 将用户角色设置为管理员
      user.roles = ['admin']
      user.save

      # 登陆成功，返回用户信息
      render json: { user_id: user.id }
    else
      # 登陆失败，返回错误信息
      render json: { error: 'Invalid email or password' }
    end
  end
end