Question

I’m writing a rails script which accepts command line parameters. One param is a relative date – i.e. 3.months.ago

This option is passed to my script as a string. How can I use that string as a relative date? My instinct is to cast it, but not sure to what…

For instance:

>> Event.count(:all, :conditions => ["created_at > ?", 3.months.ago])
=> 18883
>>
>> user_date = "3.months.ago"
>> Event.count(:all, :conditions => ["created_at > ?", user_date])
ActiveRecord::StatementInvalid: PGError: ERROR:  invalid input syntax for type timestamp: "3.months.ago"

Answer 1

Just evaluate it to get a Time instance:

[1] pry(main)> eval('3.months.ago').class
=> ActiveSupport::TimeWithZone
[2] pry(main)> eval('3.months.ago')
=> Sun, 15 Apr 2012 00:20:25 EDT -04:00
[3] pry(main)> Event.where("created_at > ?", eval('3.months.ago')).to_sql
=> "SELECT `events`.* FROM `events`  WHERE (created_at > '2012-04-15 00:22:46')"

Of course, you don’t want to eval anything that a user inputs directly. But it’s a reasonable way to handle relative dates that you construct.