counter_culture

Turbo-charged counter caches for your Rails app. Huge improvements over the Rails standard counter caches:

Updates counter cache when values change, not just when creating and destroying
Supports counter caches through multiple levels of relations
Supports dynamic column names, making it possible to split up the counter cache for different types of objects
Executes counter updates after the commit, avoiding deadlocks
Can keep a running count, or a running total

Installation

Add counter_culture to your Gemfile:

gem 'counter_culture', '~> 0.1.33'

Then run bundle install

Database Schema

You must create the necessary columns for all counter caches. You can use counter_culture's generator to create a skeleton migration:

rails generate counter_culture Category products_count

Which will generate a migration with code like the following:

add_column :categories, :products_count, :integer, :null => false, :default => 0

Note that the column must be NOT NULL and have a default of zero for this gem to work correctly.

If you are adding counter caches to existing data, you must add code to manually populate their values to the generated migration.

Usage

Simple counter-cache

class Product < ActiveRecord::Base
  belongs_to :category
  counter_culture :category
end

class Category < ActiveRecord::Base
  has_many :products
end

Now, the Category model will keep an up-to-date counter-cache in the products_count column of the categories table.

Multi-level counter-cache

class Product < ActiveRecord::Base
  belongs_to :sub_category
  counter_culture [:sub_category, :category]
end

class SubCategory < ActiveRecord::Base
  has_many :products
  belongs_to :category
end

class Category < ActiveRecord::Base
  has_many :sub_categories
end

Now, the Category model will keep an up-to-date counter-cache in the products_count column of the categories table. This will work with any number of levels.

If you want to have a counter-cache for each level of your hierarchy, then you must add a separate counter cache for each level. In the above example, if you wanted a count of products for each category and sub_category you would change the Product class to:

class Product < ActiveRecord::Base
  belongs_to :sub_category
  counter_culture [:sub_category, :category]
  counter_culture [:sub_category]
end

Customizing the column name

class Product < ActiveRecord::Base
  belongs_to :category
  counter_culture :category, :column_name => "products_counter_cache"
end

class Category < ActiveRecord::Base
  has_many :products
end

Now, the Category model will keep an up-to-date counter-cache in the products_counter_cache column of the categories table. This will also work with multi-level counter caches.

Dynamic column name

class Product < ActiveRecord::Base
  belongs_to :category
  counter_culture :category, :column_name => proc {|model| "#{model.product_type}_count" }
  # attribute product_type may be one of ['awesome', 'sucky']
end

class Category < ActiveRecord::Base
  has_many :products
end

Delta Magnitude

class Product < ActiveRecord::Base
  belongs_to :category
  counter_culture :category, column_name: :weight, delta_magnitude: proc { model.product_type == 'awesome' ? 2 : 1 }
end

class Category < ActiveRecord::Base
  has_many :products
end

Now the Category model will keep the weight column up to date: awesome products will affect it by a magnitude of 2, others by a magnitude of 1.

You can also use a static multiplier as the delta_magnitude:

class Product < ActiveRecord::Base
  belongs_to :category
  counter_culture :category, column_name: :weight, delta_magnitude: 3
end

class Category < ActiveRecord::Base
  has_many :products
end

Now adding a Product will increase the weight column in its Category by 3; deleting it will decrease it by 3.

Conditional counter cache

class Product < ActiveRecord::Base
  belongs_to :category
  counter_culture :category, :column_name => proc {|model| model.special? ? 'special_count' : nil }
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.

Totaling instead of counting

Instead of keeping a running count, you may want to automatically track a running total. In that case, the target counter will change by the value in the totaled field instead of changing by exactly 1 each time. Use the :delta_column option to specify that the counter should change by the value of a specific field in the counted object. For example, suppose the Product model table has a field named weight_ounces, and you want to keep a running total of the weight for all the products in the Category model's product_weight_ounces field:

class Product < ActiveRecord::Base
  belongs_to :category
  counter_culture :category, :column_name => 'product_weight_ounces', :delta_column => 'weight_ounces'
end

class Category < ActiveRecord::Base
  has_many :products
end

Now, the Category model will keep the counter cache in product_weight_ounces up-to-date. The value in the counter cache will be the sum of the weight_ounces values in each of the associated Product records.

The :delta_column option supports all numeric column types, not just :integer. Specifically, :float is supported and tested.

Dynamically over-writing affected foreign keys

class Product < ActiveRecord::Base
  belongs_to :category
  counter_culture :category, :foreign_key_values => 
      proc {|category_id| [category_id, Category.find_by_id(category_id).try(:parent_category).try(:id)] }
end

class Category < ActiveRecord::Base
  belongs_to :parent_category, :class_name => 'Category', :foreign_key => 'parent_id'
  has_many :children, :class_name => 'Category', :foreign_key => 'parent_id'

  has_many :products
end

Now, the Category model will keep an up-to-date counter-cache in the products_count column of the categories table. Each product will affect the counts of both its immediate category and that category's parent. This will work with any number of levels.

Updating timestamps when counts change

By default, counter_culture does not update the timestamp of models when it updates their counter caches. If you would like every change in the counter cache column to result in an updated timestamp, simply set the touch option to true like so:

  counter_culture :category, :touch => true

This can be useful when you use Rails' caching mechanism and display a counter cache's value in the cached fragment.

Manually populating counter cache values

You will sometimes want to populate counter-cache values from primary data. This is required when adding counter-caches to existing data. It is also recommended to run this regularly (at BestVendor, we run it once a week) to catch any incorrect values in the counter caches.

Product.counter_culture_fix_counts
# will automatically fix counts for all counter caches defined on Product

Product.counter_culture_fix_counts :except => :category
# will automatically fix counts for all counter caches defined on Product, except for the :category relation

Product.counter_culture_fix_counts :only => :category
# will automatically fix counts only on the :category relation on Product

# :except and :only also accept arrays of one level relations
# if you want to fix counts on a more than one level relation you need to use convention below:

Product.counter_culture_fix_counts :only => [[:subcategory, :category]]
# will automatically fix counts only on the two-level [:subcategory, :category] relation on Product

# :except and :only also accept arrays

The counter_culture_fix_counts counts method uses batch processing of records to keep the memory consumption low. The default batch size is 1000 but is configurable like so

# In an initializer
CounterCulture.config.batch_size = 100

or by passing the :batch_size option to the method call

Product.counter_culture_fix_counts :batch_size => 100

counter_culture_fix_counts returns an array of hashes of all incorrect values for debugging purposes. The hashes have the following format:

{ :entity => which model the count was fixed on,
  :id => the id of the model that had the incorrect count,
  :what => which column contained the incorrect count,
  :wrong => the previously saved, incorrect count,
  :right => the newly fixed, correct count }

counter_culture_fix_counts is optimized to minimize the number of queries and runs very quickly.

Handling dynamic column names

Manually populating counter caches with dynamic column names requires additional configuration:

class Product < ActiveRecord::Base
  belongs_to :category
  counter_culture :category, 
      :column_name => proc {|model| "#{model.product_type}_count" },
      :column_names => {
          ["products.product_type = ?", 'awesome'] => 'awesome_count',
          ["products.product_type = ?", 'sucky'] => 'sucky_count'
      }
  # attribute product_type may be one of ['awesome', 'sucky']
end

Handling over-written, dynamic foreign keys

Manually populating counter caches with dynamically over-written foreign keys (:foreign_key_values option) is not supported. You will have to write code to handle this case yourself.

Polymorphic associations

counter_culture currently does not support polymorphic associations. Check this issue for progress and alternatives.

A note on testing

counter_culture will not update counters in your automated tests if you use transactional fixtures. That's because transactional fixtures roll back all your database transactions and they are never committed. But counter_culture will only update its counters in the after_commit callback, which in this case will never run.

counter_culture itself has extensive automated tests so there should not be a need to test counter caches in your own tests. I therefore recommend removing any checks of counter caches as that will avoid this issue. If that is not an option for you, you can use the test_after_commit gem to trigger after_commit callbacks even with transactional fixtures enabled. Another option is to turn off transactional fixtures and use something like database_cleaner instead to clean your database between tests.

Contributing to counter_culture

Check out the latest master to make sure the feature hasn't been implemented or the bug hasn't been fixed yet.
Check out the issue tracker to make sure someone already hasn't requested it and/or contributed it.
Fork the project.
Start a feature/bugfix branch.
Commit and push until you are happy with your contribution.
Make sure to add tests for it. This is important so I don't break it in a future version unintentionally.
Please try not to mess with the Rakefile, version, or history. If you want to have your own version, or is otherwise necessary, that is fine, but please isolate to its own commit so I can cherry-pick around it.