Forward ActiveRecord::Relation#count to Enumerable#count

Let's say that we want to know all the deliveries in progress for an order.

The following code would do the job.

class Order
  has_many :deliveries

  def num_deliveries_in_progress
    deliveries.select { |delivery| delivery.in_progress? }.size
  end

end

But usage of count should make more sense over a select, right?

class Order
  has_many :deliveries

  def num_deliveries_in_progress
    deliveries.count { |delivery| delivery.in_progress? }
  end

end

However the changed code would return count for all the order deliveries, rather than returning only the ones in progress.

That's because ActiveRecord::Relation#count silently discards the block argument.

Rails 5.1 fixed this issue.

module ActiveRecord
  module Calculations

    def count(column_name = nil)
      if block_given?
        to_a.count { |*block_args| yield(*block_args) }
      else
        calculate(:count, column_name)
      end
    end

  end
end

So now, we can pass a block to count method.