Rails how to change status on a method?

i'm trying to change the status of Dispute object on create and update

i did the attribute inside the method but the status did not changed.

Is better to change the status in the model with callback instead on controller?

def create


   Dispute.new 

    if params[:status] == 'Open'
      dispute.status = dispute.statuses[0]
    end

    if dispute.save

       redirect_to dispute_path(@dispute)
      flash[:success] = 'Hooray'

  else
    flash[:error] = 'Error'
  redirect_to :back
end

end

on Dispute model

class Dispute < ActiveRecord::Base

  STATUSES = %w(open finished).freeze
  STATUSES.each do |method|
    define_method "#{method}?" do
      status == method
    end
  end

  def self.statuses
    STATUSES
  end

end