customer.rb

class Customer < ApplicationRecord

  has_many :following_playlists, class_name:'PlaylistFollower', dependent: :destroy

  def follow_playlist!(playlist_id)
    following_playlists.create(playlist_id: playlist_id)
  end

  def unfollow_playlist!(playlist_id)
    following_playlists.find_by(playlist_id: playlist_id).destroy
  end

  def is_following_playlist?(playlist_id)
    following_playlists.exists?(playlist_id:playlist_id)
  end

end

playlist_follower.rb

class PlaylistFollower < ApplicationRecord
  belongs_to :site
  belongs_to :playlist
  belongs_to :customer

  acts_as_tenant :site

  validates_uniqueness_to_tenant :playlist_id, scope: :customer_id
end

playlist_followers_controller.rb

class PlaylistFollowersController < ApplicationController
  before_action :redirect_if_plugin_not_activated, :set_playlist, :authenticate_customer!

  def follow
    respond_to do |format|
      if current_customer.follow_playlist! @playlist.id
        TenantEventJob.perform_later(current_tenant.id, (current_customer ? current_customer.id : nil),'followed_playlist','Playlist', @playlist.id, tenant_event_params )
        format.html{ redirect_back(fallback_location:root_path, success: 'You are now following this playlist!') }
        format.js {}
      else
        format.html{ redirect_to :back, notice: 'Oh no! Something happened' }
        format.js {}
      end
    end
  end

  def unfollow
    respond_to do |format|
      if current_customer.unfollow_playlist! @playlist.id
        format.html{ redirect_back(fallback_location:root_path, success: 'You are now unfollowing this playlist!') }
        format.js {}
      else
        format.html{ redirect_to :back, notice: 'Oh no! Something happened' }
        format.js {}
      end
    end
  end

  private

    def set_playlist
      @playlist = Playlist.find(params[:id])
    end

    def redirect_if_plugin_not_activated
      redirect_to site_root_path unless current_tenant.plugin_activated?('playlists')
    end
end