Add conditional api

README.md

@@ -190,6 +190,24 @@ Now, the ```Category``` model will keep the counter cache in ```special_count```
 
 If you would like to use this with `counter_culture_fix_counts`, make sure to also provide [the `column_names` configuration](#handling-dynamic-column-names).
 
+### Conditional counter cache shorthand
+
+You may also use a conditional API identical to [ActiveRecord's Callbacks](https://guides.rubyonrails.org/active_record_callbacks.html#conditional-callbacks) to conditionally count columns:
+
+```ruby
+class Product < ActiveRecord::Base
+  belongs_to :category
+  counter_culture :category, column_name: :special_count, if: :special?
+end
+
+class Category < ActiveRecord::Base
+  has_many :products
+end
+
+Now, the ```Category``` model will keep the counter cache in ```special_count``` up-to-date. Only products where ```special?``` returns true will affect the special_count.
+
+If you would like to use this with `counter_culture_fix_counts`, make sure to also provide [the `column_names` configuration](#handling-dynamic-column-names).
+
 ### Temporarily skipping counter cache updates
 
 If you would like to temporarily pause counter_culture, for example in a backfill script, you can do so as follows:

lib/counter_culture/counter.rb

@@ -9,7 +9,25 @@ def initialize(model, relation, options)
       @model = model
       @relation = relation.is_a?(Enumerable) ? relation : [relation]
 
-      @counter_cache_name = options.fetch(:column_name, "#{model.name.demodulize.tableize}_count")
+      @counter_cache_name = proc do |model|
+        conditions = proc do |condition|
+          case condition
+          when Symbol
+            model.public_send(condition)
+          when Proc
+            model.instance_exec(&condition)
+          else
+            raise ArgumentError, "Condition must be a symbol or a proc"
+          end
+        end
+
+        conditions_allow_change? = Array.wrap(options[:if]).all?(&conditions) &&
+          Array.wrap(options[:unless]).none?(&conditions)
+        return unless conditions_allow_change?
+
+        options.fetch(:column_name, "#{model.name.demodulize.tableize}_count")
+      end
+
       @column_names = options[:column_names]
       @delta_column = options[:delta_column]
       @foreign_key_values = options[:foreign_key_values]

spec/counter_culture_spec.rb

@@ -15,6 +15,7 @@
 require 'models/simple_dependent'
 require 'models/conditional_main'
 require 'models/conditional_dependent'
+require 'models/conditional_dependent_shorthand'
 require 'models/post'
 require 'models/post_comment'
 require 'models/post_like'
@@ -1711,6 +1712,24 @@ def yaml_load(yaml)
     ConditionalMain.find_each { |main| expect(main.conditional_dependents_count).to eq(main.id % 2 == 0 ? 3 : 0) }
   end
 
+  it "should correctly fix the counter caches for thousands of records when counter is conditional using :if/:unless" do
+    # first, clean up
+    ConditionalDependentShorthand.delete_all
+    ConditionalMain.delete_all
+
+    MANY.times do |i|
+      main = ConditionalMain.create
+      3.times { main.conditional_dependent_shorthands.create(:condition => main.id % 2 == 0) }
+    end
+
+    ConditionalMain.find_each { |main| expect(main.conditional_dependent_shorthands_count).to eq(main.id % 2 == 0 ? 3 : 0) }
+
+    ConditionalMain.order(db_random).limit(A_FEW).update_all :conditional_dependent_shorthands_count => 1
+    ConditionalDependentShorthand.counter_culture_fix_counts :batch_size => A_BATCH
+
+    ConditionalMain.find_each { |main| expect(main.conditional_dependent_shorthands_count).to eq(main.id % 2 == 0 ? 3 : 0) }
+  end
+
   it "should correctly fix the counter caches when no dependent record exists for some of main records" do
     # first, clean up
     SimpleDependent.delete_all

spec/models/conditional_dependent_shorthand.rb

@@ -0,0 +1,8 @@
+class ConditionalDependentShorthand < ActiveRecord::Base
+  belongs_to :conditional_main
+  scope :condition, -> { where(condition: true) } 
+
+  counter_culture :conditional_main, if: :condition?, column_names: -> { {
+    ConditionalDependentShorthand.condition => :conditional_dependent_shorthands_count,
+  } }
+end

spec/models/conditional_main.rb

@@ -1,3 +1,4 @@
 class ConditionalMain < ActiveRecord::Base
   has_many :conditional_dependents
+  has_many :conditional_dependent_shorthands
 end

spec/schema.rb

@@ -139,6 +139,7 @@
 
   create_table "conditional_mains", :force => true do |t|
     t.integer "conditional_dependents_count", :null => false, :default => 0
+    t.integer "conditional_dependent_shorthands_count", :null => false, :default => 0
     t.datetime "created_at"
     t.datetime "updated_at"
   end
@@ -150,6 +151,13 @@
     t.datetime "updated_at"
   end
 
+  create_table "conditional_dependent_shorthands", :force => true do |t|
+    t.integer "conditional_main_id"
+    t.boolean "condition", default: false
+    t.datetime "created_at"
+    t.datetime "updated_at"
+  end
+
   create_table "categs", :primary_key => "cat_id", :force => true do |t|
     t.integer  "posts_count",       :default => 0, :null => false
     t.datetime "created_at"