Add support for multilevel many-to-many counters

lib/counter_culture/counter.rb

@@ -182,7 +182,11 @@ def foreign_key_value(obj, relation, was = false)
         value = value.send(relation.shift)
       end
 
-      return value.try(relation_primary_key(original_relation, source: obj, was: was).try(:to_sym))
+      if value.is_a?(ActiveRecord::Associations::CollectionProxy)
+        value.map { |v| v.try(relation_primary_key(original_relation, source: obj, was: was).try(:to_sym)) }
+      else
+        value.try(relation_primary_key(original_relation, source: obj, was: was).try(:to_sym))
+      end
     end
 
     # gets the reflect object on the given relation

spec/counter_culture_spec.rb

@@ -34,6 +34,11 @@
 require 'models/group'
 require 'models/sub_group'
 require 'models/group_item'
+require 'models/many_to_many/article'
+require 'models/many_to_many/author'
+require 'models/many_to_many/reader'
+require 'models/many_to_many/authors_article'
+require 'models/many_to_many/readers_article'
 
 if ENV['DB'] == 'postgresql'
   require 'models/purchase_order'
@@ -2766,4 +2771,42 @@ def mess_up_counts
     po.reload
     expect(po.total_amount).to eq(0.0)
   end
+
+  describe "many to many association counter caches" do
+    let!(:reader) { Reader.create! }
+    let!(:author) { Author.create! }
+    let(:article) { Article.new(readers: [reader], authors: [author]) }
+
+    context "when the relation is a single-level one" do
+      context "when creating a new record" do
+        it "updates the counter cache" do
+          expect { article.save }.to change { author.reload.articles_count }.by(1)
+        end
+      end
+
+      context "when deleting an existing record" do
+        before { article.save }
+
+        it "updates the counter cache" do
+          expect { article.destroy }.to change { author.reload.articles_count }.by(-1)
+        end
+      end
+    end
+
+    context "when the relation is a multi-level one" do
+      context "when creating a new record" do
+        it "updates the counter cache" do
+          expect { article.save }.to change { author.reload.readers_count }.by(1)
+        end
+      end
+
+      context "when deleting an existing record" do
+        before { article.save }
+
+        it "updates the counter cache" do
+          expect { article.destroy }.to change { author.reload.readers_count }.by(-1)
+        end
+      end
+    end
+  end
 end

spec/models/many_to_many/article.rb

@@ -0,0 +1,7 @@
+class Article < ActiveRecord::Base
+  has_many :readers_articles, dependent: :destroy
+  has_many :authors_articles, dependent: :destroy
+
+  has_many :readers, through: :readers_articles, dependent: :destroy
+  has_many :authors, through: :authors_articles, dependent: :destroy
+end

spec/models/many_to_many/author.rb

@@ -0,0 +1,4 @@
+class Author < ActiveRecord::Base
+  has_many :authors_articles, dependent: :destroy
+  has_many :articles, through: :authors_articles, dependent: :destroy
+end

spec/models/many_to_many/authors_article.rb

@@ -0,0 +1,6 @@
+class AuthorsArticle < ActiveRecord::Base
+  belongs_to :author
+  belongs_to :article
+
+  counter_culture :author, column_name: :articles_count
+end

spec/models/many_to_many/reader.rb

@@ -0,0 +1,4 @@
+class Reader < ActiveRecord::Base
+  has_many :readers_articles, dependent: :destroy
+  has_many :articles, through: :readers_articles, dependent: :destroy
+end

spec/models/many_to_many/readers_article.rb

@@ -0,0 +1,6 @@
+class ReadersArticle < ActiveRecord::Base
+  belongs_to :reader
+  belongs_to :article
+
+  counter_culture [:article, :authors], column_name: :readers_count
+end

spec/schema.rb

@@ -281,6 +281,31 @@
     t.string  "sub_group_uuid", :null => false
   end
 
+  create_table "readers", :force => true do |t|
+    t.string "name"
+  end
+
+  create_table "articles", :force => true do |t|
+    t.string "title"
+  end
+
+  create_table "authors", :force => true do |t|
+    t.string "name"
+
+    t.integer "articles_count", default: 0, null: false
+    t.integer "readers_count", default: 0, null: false
+  end
+
+  create_table "readers_articles", :force => true do |t|
+    t.integer "reader_id", null: false
+    t.integer "article_id", null: false
+  end
+
+  create_table "authors_articles", :force => true do |t|
+    t.integer "author_id", null: false
+    t.integer "article_id", null: false
+  end
+
   if ENV['DB'] == 'postgresql' && Gem::Version.new(Rails.version) >= Gem::Version.new('5.0')
     create_table :purchase_orders, :force => true do |t|
       t.money "total_amount", scale: 2, default: "0.0", null: false