ActiveRecord time truncation

example.rb

gem 'activerecord', '4.2.5'
require 'active_record'
require 'minitest/autorun'
require 'logger'

ActiveRecord::Base.logger = Logger.new(STDOUT)
ActiveRecord::Base.establish_connection(
  :adapter  => 'postgresql',
  :database => 'x'
)

ActiveRecord::Schema.define do
  create_table :users, :force => true do |t|
    t.timestamp :updated_at, null: false
  end
end

class User < ActiveRecord::Base
end

class TestMe < MiniTest::Unit::TestCase
  def test_preserves_precise_data_time
    time = Time.utc(2016, 4, 19,  7, 9, 45, 852407) # '2016-04-19 07:09:45.852407'
    deserialised = Time.at(time.to_f)

    User.create!(updated_at: time)

    assert_equal 0, User.where('updated_at > ?', deserialised).count
  end
end

output.txt

-- create_table(:users, {:force=>true})
D, [2016-04-19T18:53:17.307846 #34798] DEBUG -- :    (1.6ms)  DROP TABLE "users"
D, [2016-04-19T18:53:17.311649 #34798] DEBUG -- :    (3.6ms)  CREATE TABLE "users" ("id" serial primary key, "updated_at" timestamp NOT NULL)
   -> 0.0220s
MiniTest::Unit::TestCase is now Minitest::Test. From tmp/a.rb:21:in `<main>'
Run options: --seed 64840

# Running:

D, [2016-04-19T18:53:17.407264 #34798] DEBUG -- :    (0.1ms)  BEGIN
D, [2016-04-19T18:53:17.411897 #34798] DEBUG -- :   SQL (0.5ms)  INSERT INTO "users" ("updated_at") VALUES ($1) RETURNING "id"  [["updated_at", "2016-04-19 07:09:45.852407"]]
D, [2016-04-19T18:53:17.412517 #34798] DEBUG -- :    (0.2ms)  COMMIT
D, [2016-04-19T18:53:17.413931 #34798] DEBUG -- :    (0.4ms)  SELECT COUNT(*) FROM "users" WHERE (updated_at > '2016-04-19 07:09:45.852406')
F

Finished in 0.014022s, 71.3158 runs/s, 71.3158 assertions/s.

  1) Failure:
TestMe#test_preserves_precise_data_time [tmp/a.rb:28]:
Expected: 0
  Actual: 1

1 runs, 1 assertions, 1 failures, 0 errors, 0 skips