database_view.sql

CREATE VIEW product_stats AS
SELECT organization_id, 
       SUM(CASE WHEN status = 'active' THEN 1 END) active_count, 
       SUM(CASE WHEN status = 'inactive' THEN 1 END) inactive_count
FROM products
GROUP BY organization_id

database_view_model.rb

class ProductSummary < ActiveRecord::Base
  include ReadOnlyModel

  belongs_to :organization

  def ==(other)
    self.class == other.class && attributes == other.attributes
  end
  alias :eql? :==
 
  def hash
    attributes.hash
  end
end

inline_view_model.rb

class ProductSummary < ActiveRecord::Base
  include ReadOnlyModel

  belongs_to :organization

  default_scope { set_from_clause }

  def ==(other)
    self.class == other.class && attributes == other.attributes
  end
  alias :eql? :==
 
  def hash
    attributes.hash
  end

  private

  def self.set_from_clause
    query = Product.select(:organization_id).group(:organization_id)
    Product::VALID_STATUSES.each do |status|
      query = query.select("SUM(CASE WHEN status = '#{status}' THEN 1 END) #{status}_count")
    end

    from("(#{query.to_sql}) AS #{table_name}")
  end

  def self.columns
    cols = [ActiveRecord::ConnectionAdapters::Column.new('organization_id', nil, :integer)]
    Product::VALID_STATUSES.each do |status|
      cols << ActiveRecord::ConnectionAdapters::Column.new("#{status}_count", nil, :integer)
    end
    cols
  end
end

naive.rb

org_infos = Organization.limit(25).map do |org|
  {
    id: org.id, 
    name: org.name, 
    active_product_count: org.products.active.count, 
    inactive_product_count: org.products.inactive.count
  }
end

organization.rb

class Organization < ActiveRecord::Base
  has_many :products
end

organization2.rb

class Organization < ActiveRecord::Base
  has_many :products
  has_one :product_summary
end

product.rb

class Product < ActiveRecord::Base
  belongs_to :organization

  VALID_STATUSES = [:active, :inactive]

  scope :active, where(state: :active)
  scope :inactive, where(state: :inactive)
end

with_database_view.rb

org_infos = Organization.includes(:product_summary).limit(25).map do |org|
  {
    id: org.id, 
    name: org.name, 
    active_product_count: org.product_summary.active_count, 
    inactive_product_count: org.product_summary.inactive_count
  }
end