gistfile1.rb

class Group::InvitationsController < ApplicationController
  load_resource :group
  before_filter :authorize_invitations, only: [:new, :create]

  def new
    already_invited_user_ids = @group.group_invitations.by_user(current_user).pluck(:invitee_id) | @group.user_ids
    @to_invite = { friends: current_user.friends.includes(:profile),
                   followers: current_user.followers.includes(:profile),
                   without_ids: already_invited_user_ids }
  end

  def create
    invitee_ids = params[:group_invitation][:invitee_ids]
    invitees = User.where(id: invitee_ids)
    invitees.each do |invitee|
      GroupInvitation.create do |invitation|
        invitation.inviter = current_user
        invitation.invitee = invitee
        invitation.group = @group
      end
    end
    respond_with @group
  end

  def update
    invitation = GroupInvitation.find(params[:id])
    invitation.update_attribute(:status, params[:status])
    respond_with @group
  end

  def resource
    GroupInvitation.new
  end

  private

  def authorize_invitations
    authorize! :invite_users, @group
  end

end