DateTime objects are truncating milliseconds

[coneybeare]

I have a test where I create an object, grab the json response (as rendered by acts_as_api), then compare it's values against the object's attributes.to_json.

While this works for nearly all objects, I have noticed something very weird on Rails 4 with DateTime objects.

>> puts apple.updated_at
2014-02-07 18:35:55 UTC
>> puts apple.updated_at.to_json
"2014-02-07T18:35:55.423Z"

...
(make get :show call to server, returning json on apple)
...

>> puts json['apple']['updated_at']
"2014-02-07T18:35:55.000Z"

Here you can see that the controller, calling render_for_api, on the same object, is zeroing (or possible rounding) the milliseconds at the end. Otherwise, they are equal. Do you have any ideas as to why, or how I can resolve this?

[fabrik42]

Hi Matt,

I don't think milliseconds in as_json/to_json is a default setting. Did you patch anything, e.g. ActiveSupport::TimeWithZone?

Generally speaking - there is no converter in acts_as_api itself to format DateTime or similar objects. This task is done by Rails itself.

[javiyu]

Is your database engine truncating the value?

class User < ActiveRecord::Base
  acts_as_api

  api_accessible :public do |template|
     template.add :email
     template.add :current_sign_in_at
   end  
end

class UsersController < ApplicationController
  respond_to :json

  def index
    @users = User.all
    @users << User.new(current_sign_in_at: Time.now)
    respond_with(@users, :api_template => :public, :root => :users)
  end
end

Using MySQL I get truncated values for all records except for the one I'm adding at the end of the collection (which is not saved)

[coneybeare]

That's exactly what is happening. MySQL doesn't store milliseconds so when read from disk it gets truncated. The object I am comparing it to is in memory newly created.

[fabrik42]

It seems like Rails itself omits milliseconds when rendering a time as json.

This is from a Rails 3.2 app using Postgres (which stores milliseconds)

User.last.updated_at.as_json
# => "2014-02-09T11:37:26Z" 

User.last.updated_at_before_type_cast
# => "2014-01-31 11:37:26.061182"

User.last.updated_at.usec
# => 61182 

If you need to render milliseconds, you probably need to overwrite ActiveSupport::TimeWithZone::as_json

[coneybeare]

I don't need to, I just needed them to match for rspec purposes. No biggie