Setting a DateTime to UTC rather than having it write the current system time

Question

I have a class method like this:

  def self.seed
    InventoryPeriod.delete_all
    (1..8).each do |i|
      self.create! name: "name#{i}", start_datetime: DateTime.new(2014,i,1), end_datetime:DateTime.new(2014,i,-1), location_id: 12
    end
  end

but it seems like it should be writing to the database in UTC (DateTime.new(2014,i,1).utc doesn't do it) but it doesn't and basically is off by 8 hours.

For example:

| 51 | 2014-08-01 00:00:00 | 2014-08-31 00:00:00

but should be:

| 51 | 2014-07-31 16:00:00 | 2014-08-30 16:00:00

What's the best solution for this? Hopefully, some rails thing that I'm not aware of - would seem like there should be since it must be so common. Or do I manually adjust by the necessary hours?

Answer 1

If your attributes are time zone aware and you desire to skip time zone conversion for certain attributes then you can do following:

Model_Name.skip_time_zone_conversion_for_attributes = [:attribute_name]

OR Generally you can call this inside the model:

skip_time_zone_conversion_for_attributes

Ref: http://api.rubyonrails.org/v3.0.0/classes/ActiveRecord/Timestamp.html

For this to work, please make sure you have not specified any specific Time Zone in application.rb file.

Or if you want a fixed Timezone other than UTC:

Please refer How to change default timezone for Active Record in Rails?

Hope it helps :)

Answer 2

The problem is that when you're doing DateTime.new(y,m,d), the time zone is defaulting to UTC. So in your example, it is storing the DateTime in UTC, just 8 hours off from what you had expected.

Doing this

DateTime.new(2014,8,1,0,0,0, '+8')
DateTime.new(2014,8,-1,0,0,0, '+8')
DateTime.new(2014,8,1,0,0,0, '+8').getutc
DateTime.new(2014,8,-1,0,0,0, '+8').getutc

Will give this result

2014-08-01T00:00:00+08:00
2014-08-31T00:00:00+08:00
2014-07-31T16:00:00+00:00
2014-08-30T16:00:00+00:00

Here it is plugged into your code.

(1..8).each do |i|
  self.create! name: "name#{i}", start_datetime: DateTime.new(2014,i,1,0,0,0, '+8').getutc, end_datetime: DateTime.new(2014,i,-1,0,0,0, '+8').getutc, location_id: 12
end