Comparing Identical Datetime Objects in Ruby -- Why Are These Two Datetime.Now's Not Equal

Comparing identical DateTime objects in ruby -- why are these two DateTime.now's not equal?

Possible clue; the act of saving and reloading truncates the seconds_fraction part of the DateTime. The date field becomes an instance of ActiveSupport::TimeWithZone. Just saving without reloading doesn't do this; the real DateTime object is still there.

2.0.0-p195 :001 > dt            =  DateTest.create
2.0.0-p195 :002 > right_now     =  DateTime.now
2.0.0-p195 :004 > dt.created_at =  right_now
2.0.0-p195 :005 > dt.created_at == right_now
 => true 

2.0.0-p195 :006 > dt.save
2.0.0-p195 :007 > dt.created_at == right_now
 => true 

2.0.0-p195 :008 > dt = DateTest.find(dt.id)
2.0.0-p195 :009 > dt.created_at == right_now
 => false 

Edit: of course calling models.each is going to load the models there and then because of the lazy loading behaviour. Props to the other answerer. As an experiment, try setting models to Model.where(resource: resource).to_a.

Compare datetime objects in Rails

Operator === is defined in Date class in Ruby which is parent class of DateTime. Operator === Returns true if they are the same day which is the case in your example. See description

Now to answer other part of your question about comparing two DateTime, see this answer. Which states that the act of saving and reloading datetime in database truncates the seconds_fraction part of the DateTime.

You can verify that in your rails console by below code -

obj1 = Foo.order("created_at").last.created_at.to_datetime
obj2 = DateTime.parse("2014-09-14 01:12:03 +0200")

obj1.sec > obj2.sec #comparing seconds, returns false. Both equal
obj1.sec_fraction > obj2.sec_fraction #should return true. Not equal.

Comparing dates in rails

Yes, you can use comparison operators to compare dates e.g.:

irb(main):018:0> yesterday = Date.new(2009,6,13)
=> #<Date: 4909991/2,0,2299161>
irb(main):019:0> Date.today > yesterday
=> true

But are you trying to compare a date to a datetime?

If that's the case, you'll want to convert the datetime to a date then do the comparison.

I hope this helps.

Ruby Comparing Time objects considers date. How to avoid that?

You can just modulus the days off to get the remaining time value.

t1 = Time.now
t2 = t2 = Time.at(Time.now.to_i - (5*24*3600))  # later time in day but previous date
tod1 = t.to_i % (24*3600)
=> 69734
tod2 = t2.to_i % (24*3600)
=> 69912

we can clearly see that t2 is a later time of day or clock time if you will and the modulus operation is very clear if you know anything about the unix epoch.

Rails 3, comparing only the dates of two datetime columns in rails

Declare a new attribute that contains just the date:

class WhateverModel < ActiveRecord::Base
  ...
  def viewed_date_only
    viewed_date.to_date
  end
end

Use that for your comparison in the controller or wherever.

How rails compare with datetime with timestamp

So far as I understand you should do like this (to compare an integer with DateTime convert it to integer also)-

  if user.created_at.to_i >= 1563724800
    do sth
  end

Or you should compare reversely (convert an integer to DateTime)

  if user.created_at >= Time.at(1563724800)
    do sth
  end

time.to_i => int time as an integer number of seconds since epoch.

Time.at(seconds) => time => new time object with the given number of seconds

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