In Mongoid, are there any differences in the Date, Time, DateTime, and TimeWithZone field types?

Question

The documentation mentions the four types of time related field types (http://mongoid.org/en/mongoid/docs/documents.html#fields). In other databases, I can see how these fields are going to be difference types in the database but for MongoDB aren't they all going to be Date types? Is this just for consistency with ActiveRecord?

Answer 1

There are almost no difference between them, all of them wrap Time type. You can change DateTime, Date or TimeWithZone to get instances of this types after unserializing from mongo.

Mongoid extends this classes to add demongoize/mongoize methods for data binding. So the only difference is in implementation.

So Time implementation

def demongoize(object)
  return nil if object.blank?
  object = object.getlocal unless Mongoid::Config.use_utc?
  if Mongoid::Config.use_activesupport_time_zone?
    object = object.in_time_zone(Mongoid.time_zone)
  end
  object
end

def mongoize(object)
  return nil if object.blank?
  begin
    time = object.__mongoize_time__
    if object.respond_to?(:sec_fraction)
      ::Time.at(time.to_i, object.sec_fraction * 10**6).utc
    elsif time.respond_to?(:subsec)
      ::Time.at(time.to_i, time.subsec * 10**6).utc
    else
      ::Time.at(time.to_i, time.usec).utc
    end
  rescue ArgumentError
    EPOCH
  end
end

Date implementation

def demongoize(object)
  ::Date.new(object.year, object.month, object.day) if object
end


def mongoize(object)
  unless object.blank?
    begin
      time = object.__mongoize_time__
      ::Time.utc(time.year, time.month, time.day)
    rescue ArgumentError
      EPOCH
    end
  end
end

You can check other implemetations

https://github.com/mongoid/mongoid/blob/master/lib/mongoid/extensions/date.rb#L46 https://github.com/mongoid/mongoid/blob/master/lib/mongoid/extensions/date_time.rb#L49 https://github.com/mongoid/mongoid/blob/master/lib/mongoid/extensions/time.rb#L48 https://github.com/mongoid/mongoid/blob/master/lib/mongoid/extensions/time_with_zone.rb#L32