Question

Is there a way to make this method more efficient? I am querying a large number of transactions and it seems inefficient to perform a separate activerecord query for each period.

Should I make a single query for the whole day and sort through the results, grouping them by period? If so, what’s the most efficient way to do this? Look forward to your thoughts.

def self.transactions(period)
  today = Date.today
  time1 = Time.utc(today.year, today.month, today.day, 9, 30, 0)
  time2 = Time.utc(today.year, today.month, today.day, 16, 0, 0)
  transactions_by_period = {}

  while time1 < time2
    transactions = self.where("created_at >= ? and created_at <= ?", time1, time2)
    transactions_by_period[time1] = transactions
    time1 += period
  end

return transactions_by_period
end

#todays_transactions_by_hour = Stock.transactions(1.hour)

Answer 1

First off, you can use ranges for nicer queries. I’d also rename time1 and time2 to start and finish

transactions = self.where(:created_at => start..finish)

Then you can reduce this to get them by periods.

transactions.reduce(Hash.new{|h, k| h[k] = []) do |periods, transaction|
  # Calculate how many periods have gone by for this transaction
  offset = (transaction.created_at - start).to_i / period
  # Find the actual period
  transaction_period = start + offset * period
  periods[transaction_period] << transaction
  periods
end

Edit

I haven’t tested the code, it is shown more for the logic