Counter Cache With Conditions

class Message < ActiveRecord::Base
  belongs_to :folder, :counter_cache => true # rails default counter cache
  # hash syntax
  # counter_cache_with_conditions :association, :association_column_name, attribute: value
  counter_cache_with_conditions :folder, :unread_messages_count, unread: true

  # lambda syntax
  # counter_cache_with_conditions :association, :association_column_name, [:attribute], lambda{|attribute| ... }
  # lambda syntax need [:used_attributes_array] because it need to track changes, and lambda will be called only when attributes are changed
  counter_cache_with_conditions :folder, :unread_messages_count, [:read_at], lambda{|read_at| !read_at }

end

# hash syntax
counter_cache_with_conditions :folder, :unread_messages_count, :unread => true
counter_cache_with_conditions :folder, :archived_messages_count, status: 'archived'

# lambda syntax
counter_cache_with_conditions :folder, :unread_messages_count, [:read, :source], lambda{|read, source| read == false && source == 'message'}
counter_cache_with_conditions :folder, :published_events_count, [:published_at], lambda{|published_at| published_at != nil }

belongs_to :folder
# same as rails default counter cache
counter_cache_with_conditions :folder, :messages_count