gistfile1.rb

#controller

def create
    @party = Party.new(party_params)
    @party.captain_id = @user.id

    if @party.save
      @user.join_party(@party)
      respond_to do |format|
        format.html { redirect_to @party, notice: 'Party was successfully created.' }
        format.json { render :show, status: :created, location: @party }
      end
    else
      respond_to do |format|
        format.html { render :new }
        format.json { render json: @party.errors, status: :unprocessable_entity }
      end
    end
  end
  
  
#method from model

  def join_party(party)
    if self.online?
      self.update(current_party_id: party.id)
      self.join_party
    end
  end