tags: update category cache whenever category changes.

Do `update_category_cache_for_all` in a callback instead of calling it
manually everywhere.

app/controllers/tags_controller.rb

@@ -36,7 +36,6 @@ class TagsController < ApplicationController
     @tag = Tag.find(params[:id])
     check_privilege(@tag)
     @tag.update_attributes(params[:tag], :as => CurrentUser.role)
-    @tag.update_category_cache_for_all
     respond_with(@tag)
   end
 

app/logical/alias_and_implication_importer.rb

@@ -117,7 +117,6 @@ private
           tag = Tag.find_by_name(token[1])
           tag.category = Tag.categories.value_for(token[2])
           tag.save
-          tag.update_category_cache_for_all
 
         else
           raise "Unknown token: #{token[0]}"

app/models/tag.rb

@@ -15,6 +15,8 @@ class Tag < ApplicationRecord
   validates :name, uniqueness: true, tag_name: true, on: :create
   validates_inclusion_of :category, in: TagCategory.category_ids
 
+  after_save :update_category_cache_for_all, if: :category_changed?
+
   module ApiMethods
     def to_legacy_json
       return {
@@ -221,8 +223,7 @@ class Tag < ApplicationRecord
           tag.update_category_cache
 
           if category_id != tag.category && !tag.is_locked? && ((CurrentUser.is_builder? && tag.post_count < 10_000) || tag.post_count <= 50)
-            tag.update_column(:category, category_id)
-            tag.update_category_cache_for_all
+            tag.update_attribute(:category, category_id)
           end
         end
 

app/models/tag_alias.rb

@@ -173,7 +173,6 @@ class TagAlias < TagRelationship
   def ensure_category_consistency
     if antecedent_tag.category != consequent_tag.category && antecedent_tag.category != Tag.categories.general
       consequent_tag.update_attribute(:category, antecedent_tag.category)
-      consequent_tag.update_category_cache_for_all
     end
 
     true

test/unit/tag_test.rb

@@ -112,11 +112,9 @@ class TagTest < ActiveSupport::TestCase
 
     should "reset its category after updating" do
       tag = FactoryGirl.create(:artist_tag)
-      tag.update_category_cache_for_all
       assert_equal(Tag.categories.artist, Cache.get("tc:#{Cache.hash(tag.name)}"))
 
       tag.update_attribute(:category, Tag.categories.copyright)
-      tag.update_category_cache_for_all
       assert_equal(Tag.categories.copyright, Cache.get("tc:#{Cache.hash(tag.name)}"))
     end