Admin Conditions In Devise with Rails 5

I have created an admin user in my app by adding a giving admin a boolean value. The problem is when i set a user to be admin , they can't delete or edit the post in the app although i have set a condition in the show page of the post. Note that i am using the Deivse gem for user authentication. Here's my code:

BurgersController.rb

class BurgersController < ApplicationController
  before_action :authenticate_user! , except: [:index,:show,:search]
  before_action :set_burger, only: [:show, :edit, :update, :destroy,:upvote]
  before_action :check_user , only: [:edit,:update,:destroy]


  # GET /burgers
  # GET /burgers.json

   def search
    if params[:search].present?
    @burgers = Burger.search(params[:search])
    else
    @burgers = Burger.all
    end
  end
    def index
     if params[:tag]
      @burgers = Burger.tagged_with(params[:tag])
    else
      @burgers = Burger.all
    end
  end

  # GET /burgers/1
  # GET /burgers/1.json
  def show
  end

  # GET /burgers/new
 def new
    @burger = Burger.new
  end

  # GET /burgers/1/edit
  def edit
  end

  # POST /burgers
  # POST /burgers.json
  def create
    @burger = Burger.new(burger_params)
    @burger.user_id = current_user.id

    respond_to do |format|
      if @burger.save
        format.html { redirect_to @burger, notice: 'Burger was successfully created.' }
        format.json { render :show, status: :created, location: @burger }
      else
        format.html { render :new }
        format.json { render json: @burger.errors, status: :unprocessable_entity }
      end
    end
  end

  # PATCH/PUT /burgers/1
  # PATCH/PUT /burgers/1.json
  def update
    respond_to do |format|
      if @burger.update(burger_params)
        format.html { redirect_to @burger, notice: 'Burger was successfully updated.' }
        format.json { render :show, status: :ok, location: @burger }
      else
        format.html { render :edit }
        format.json { render json: @burger.errors, status: :unprocessable_entity }
      end
    end
  end

  # DELETE /burgers/1
  # DELETE /burgers/1.json
  def destroy
    @burger.destroy
    respond_to do |format|
      format.html { redirect_to burgers_url, notice: 'Burger was successfully destroyed.' }
      format.json { head :no_content }
    end
  end

  def upvote
      @burger.upvote_by current_user
    redirect_to :back
  end

  private
    # Use callbacks to share common setup or constraints between actions.
    def set_burger
      @burger = Burger.find(params[:id])
    end

    # Never trust parameters from the scary internet, only allow the white list through.
    def burger_params
      params.require(:burger).permit(:name, :resturant, :place, :price,:image,:tag_list)
    end

    def check_user
      unless @burger.user == current_user || current_user.admin?
        redirect_to root_url , alert: "Sorry this listing belongs to someone else"
      end
    end

end

views/burger/show.html.erb

 <div class="row">
      <div class="col-md-12">
        <div class="thumbnail">  
            <%= image_tag @burger.image_url.to_s, class: 'center-block'%>
        </div>

      </div>
        <div class="col-md-6">
            <h2><%= @burger.name %><br></h2>
            <%= @burger.resturant %><br>
            <%= @burger.place %><br>
            <%= number_to_currency(@burger.price, raise: true) %><br>
          <p>Tags: <%= @burger.tag_list %></p>
        </div>



      </div>
     <% if user_signed_in? && current_user == @burger.user || current_user.try(:admin?) %>
      <%= link_to 'Edit', edit_burger_path(@burger) %> |
      <%= link_to 'Back', burgers_path %>
      <%= link_to 'Delete', @burger, method: :delete, data: {confirm: "Are you Sure ?"} %>
      <%end%>

    </div>

</div>

schema.rb

create_table "users", force: :cascade do |t|
    t.string   "email",                  default: "",    null: false
    t.string   "encrypted_password",     default: "",    null: false
    t.string   "reset_password_token"
    t.datetime "reset_password_sent_at"
    t.datetime "remember_created_at"
    t.integer  "sign_in_count",          default: 0,     null: false
    t.datetime "current_sign_in_at"
    t.datetime "last_sign_in_at"
    t.string   "current_sign_in_ip"
    t.string   "last_sign_in_ip"
    t.datetime "created_at",                             null: false
    t.datetime "updated_at",                             null: false
    t.string   "name"
    t.boolean  "admin",                  default: false
    t.index ["email"], name: "index_users_on_email", unique: true
    t.index ["reset_password_token"], name: "index_users_on_reset_password_token", unique: true
  end