Add a destroyable scope and a destroyable? method to List model

app/controllers/projects/boards/lists_controller.rb

@@ -3,7 +3,6 @@ module Projects
     class ListsController < Boards::ApplicationController
       before_action :authorize_admin_list!, only: [:create, :update, :destroy, :generate]
       before_action :authorize_read_list!, only: [:index]
-      before_action :load_list, only: [:update, :destroy]
 
       def index
         render json: serialize_as_json(project.board.lists)
@@ -20,9 +19,10 @@ module Projects
       end
 
       def update
+        list = project.board.lists.find(params[:id])
         service = ::Boards::Lists::MoveService.new(project, current_user, move_params)
 
-        if service.execute(@list)
+        if service.execute(list)
           head :ok
         else
           head :unprocessable_entity
@@ -30,9 +30,10 @@ module Projects
       end
 
       def destroy
+        list = project.board.lists.destroyable.find(params[:id])
         service = ::Boards::Lists::DestroyService.new(project, current_user, params)
 
-        if service.execute(@list)
+        if service.execute(list)
           head :ok
         else
           head :unprocessable_entity
@@ -59,10 +60,6 @@ module Projects
         return render_403 unless can?(current_user, :read_list, project)
       end
 
-      def load_list
-        @list = project.board.lists.find(params[:id])
-      end
-
       def list_params
         params.require(:list).permit(:label_id)
       end

app/models/list.rb

@@ -9,7 +9,13 @@ class List < ActiveRecord::Base
   validates :label_id, uniqueness: { scope: :board_id }, if: :label?
   validates :position, numericality: { only_integer: true, greater_than_or_equal_to: 0 }, if: :label?
 
-  before_destroy :can_be_destroyed, unless: :label?
+  before_destroy :can_be_destroyed
+
+  scope :destroyable, -> { where(list_type: list_types[:label]) }
+
+  def destroyable?
+    label?
+  end
 
   def title
     label? ? label.name : list_type.humanize
@@ -18,6 +24,6 @@ class List < ActiveRecord::Base
   private
 
   def can_be_destroyed
-    false
+    destroyable?
   end
 end

app/services/boards/lists/destroy_service.rb

@@ -2,7 +2,7 @@ module Boards
   module Lists
     class DestroyService < Boards::BaseService
       def execute(list)
-        return false unless list.label?
+        return false unless list.destroyable?
 
         list.with_lock do
           decrement_higher_lists(list)

spec/models/list_spec.rb

@@ -54,6 +54,26 @@ describe List do
     end
   end
 
+  describe '#destroyable?' do
+    it 'retruns true when list_type is set to label' do
+      subject.list_type = :label
+
+      expect(subject).to be_destroyable
+    end
+
+    it 'retruns false when list_type is set to backlog' do
+      subject.list_type = :backlog
+
+      expect(subject).not_to be_destroyable
+    end
+
+    it 'retruns false when list_type is set to done' do
+      subject.list_type = :done
+
+      expect(subject).not_to be_destroyable
+    end
+  end
+
   describe '#title' do
     it 'returns label name when list_type is set to label' do
       subject.list_type = :label