angel.rb

# members_controller.rb
class MembersController < ApplicationController
  def destroy
    if !checkadmin? then return end
    @member = Member.find(params[:id])
    @member.destroy

    respond_to do |format|
      format.html { redirect_to members_url }
      format.json { head :no_content }
    end
  end
end

# application_controller.rb
class ApplicationController < ActionController::Base
  def checkadmin?
    if session[:login].admin then
      return true
    else
      redirect_to '/members/' + session[:login].id.to_s
      return false
    end
  end
end

sample.rb

# members_controller.rb
class MembersController < ApplicationController
  before_action :redirect_to_member_page, unless: -> { current_member.admin? }, only: %i(destroy)

  def destroy
    @member = Member.find(params[:id])
    @member.destroy

    respond_to do |format|
      format.html { redirect_to members_url }
      format.json { head :no_content }
    end
  end
end

# application_controller.rb
class ApplicationController < ActionController::Base
  helper_method :current_member

  private
  def current_member
    @current_member ||= Member.find_by(id: session[:member_id])
  end

  def redirect_to_member_page
    redirect_to member_url(current_member.id)
  end
end