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.

1
2class Order
3  has_many :deliveries
4
5  def num_deliveries_in_progress
6    deliveries.select { |delivery| delivery.in_progress? }.size
7  end
8
9end
10
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But usage of count should make more sense over a select, right?

1
2class Order
3  has_many :deliveries
4
5  def num_deliveries_in_progress
6    deliveries.count { |delivery| delivery.in_progress? }
7  end
8
9end
10
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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.

1
2module ActiveRecord
3  module Calculations
4
5    def count(column_name = nil)
6      if block_given?
7        to_a.count { |*block_args| yield(*block_args) }
8      else
9        calculate(:count, column_name)
10      end
11    end
12
13  end
14end
15
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So now, we can pass a block to count method.