Given a timestamp, how to get 1 month ago

Question

I'm trying to build a method where I pass a month and can then query for the previous month dynamically.

total_churn(month)
   last_month = month - 1
   companies = Company.where("created_at BETWEEN '#{last_month}' AND '#{month}')
   return companies.count
 end

How do I pass the method 'month' in a way where I can dynamically determine the last month using Ruby on Rails?

Answer 1

My suggestion: accept a date rather than a month.
total_churn(date)
   month_previous = date - 1.month
   companies = Company.where("created_at BETWEEN ? AND ?, '#{month_previous}', '#{date}')
   return companies.count
end

Current month:
Time.now.month
Date.today.month

Time or day one month ago:
(Time.now - 1.month).month
(Date.today - 1.month).month

...also equivalent to:
Time.now.month - 1
Date.today.month - 1

Previous month for any given date:
@date - 1.month

I would personally build your method to accept a date rather than just a month number. As long as the created_at field is storing dates, you'll need to give the query two dates for it to run, even if those dates are the 1st.