Counting the number of queries performed

Question

I\'d like to test that a certain piece of code performs as few SQL queries as possible.

ActiveRecord::TestCase seems to have its own assert_querie

Answer 1

My vision of Ryan's script (cleaned up a bit and wrapped in a matcher), hope it is still actual for someone:

I put this to spec/support/query_counter.rb

module ActiveRecord
  class QueryCounter

    attr_reader :query_count

    def initialize
      @query_count = 0
    end

    def to_proc
      lambda(&method(:callback))
    end

    def callback(name, start, finish, message_id, values)
      @query_count += 1 unless %w(CACHE SCHEMA).include?(values[:name])
    end

  end
end

and this to spec/support/matchers/exceed_query_limit.rb

RSpec::Matchers.define :exceed_query_limit do |expected|

  match do |block|
    query_count(&block) > expected
  end

  failure_message_for_should_not do |actual|
    "Expected to run maximum #{expected} queries, got #{@counter.query_count}"
  end

  def query_count(&block)
    @counter = ActiveRecord::QueryCounter.new
    ActiveSupport::Notifications.subscribed(@counter.to_proc, 'sql.active_record', &block)
    @counter.query_count
  end

end

Usage:

expect { MyModel.do_the_queries }.to_not exceed_query_limit(2)