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Dase gem provides includes_count_of method on a relation, which works similar to ActiveRecord's preload method and solves N+1 query problem when counting records in has_many ActiveRecord associations.


Given this data in the DB: Dase example

and this Rails model definition

class Author
  has_many :articles

you can now write this:

  authors = Author.includes_count_of(:articles)
  billy = authors.first    # => #<Author name: 'Billy'>                
  billy.articles_count     # => 2                

with conditions on associated records (only articles in year 2012)

  Author.includes_count_of(:articles, where: {year: 2012} ) 

using lambda syntax (in v4.1 and greater)

  Author.includes_count_of(:articles, -> { where(year: 2012) } )

with renamed counter method

  Author.includes_count_of(:articles, -> { where(year: 2012) }, as: :number_of_articles_in_2012)

with multiple associations counted at once

  Author.includes_count_of(:articles, :photos, :tweets)


Rails version Add this to Gemfile
3.2.x gem 'dase', '~> 3.2.0'
4.0.x ----- N/A -----
4.1.x gem 'dase', '~> 4.1.0'
4.2.0.beta2 gem 'dase', :github => 'vovayartsev/dase', :branch => 'rails-4-2'

Under the hood

When a relation is "materialized", we run a custom preloader which calculates the hash of counters in a single SQL query like this:

  counters_hash = Article.where(:year => 2012).count(:group => :author_id)

then we add counters to the parent records like this:

  define_method(:articles_count) { counters_hash[] || 0 }

Alternative approaches

Dase calculates counters dynamically every time you make an SQL query. It makes an extra SQL query for each association processed. These alternatives may be more efficient:

Name origin

The gem is named by the german mathematician Johann Dase, who was a mental calculator and could add and multiply numbers very quickly.


  1. Fork it
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  3. Commit your changes (git commit -am 'Add some feature')
  4. Push to the branch (git push origin my-new-feature)
  5. Create new Pull Request

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