app/controllers/mr_controller.rb
class MrController < ApplicationController
def show
project = current_user.projects.joins(:merge_requests).where('merge_requests.id = ?', params[:id]).first
raise ActiveRecord::RecordNotFound, 'Merge request not found.' if project.nil?
redirect_to("/projects/#{project.id}/merge_requests/#{params[:id]}")
end
end