Ruby on rails, MVC, where to put derivative data? - ruby-on-rails

Question

I'm writing a super simple web application that presents different counters for different events. My database table is filled with records representing the different events. the table has 2 colums name and date
Now before I can present the counters for every event, I need to
calculate the time left to its date
and make a string that either says something like 5d, 4h, 23m or completed
Where would you guys put this logic? Please bear with me, I'm a beginner.
ps. I'm trying to make a proper MVC application with Ruby on Rails

Answer 1

Sometimes the answer to "does this go in the model, the view, or the controller?" is "no".
Like others have said - you want the controller to be as thin as possible. It's job is to relay 'events' and do basic set up of other objects. According to conventional wisdom, the model should encapsulate your business logic. In Rails, a model usually does both persistence and business logic. In other words, if you have rules for how data is to be manipulated or how it is to be aggregated, that goes in the model. On the other hand, people have started arguing that managing both persistence and business logic is too much responsibility for one object.
The responsibilities you describe are about presenting values. To do this you could use the Presenter or Decorator pattern. In essence, you create a class of object whose responsibility is to take data from another object and prepare it for presentation. The Draper gem provides some utilities for doing just this.

Answer 2

In your event.rb, create a method called time_left (taken from https://stackoverflow.com/a/19596579/1489088):
def self.time_left
# Calculate time left for event start
current_time = Time.now
# date is retrieving the date for your model, but it has to be a datetime field and not a date field.
seconds_diff = (date - current_time).to_i.abs
hours = seconds_diff / 3600
seconds_diff -= hours * 3600
minutes = seconds_diff / 60
seconds_diff -= minutes * 60
seconds = seconds_diff
"#{hours.to_s.rjust(2, '0')}:#{minutes.to_s.rjust(2, '0')}:# {seconds.to_s.rjust(2, '0')}"
end
Why in your model, simply because this calculation is specific to your events, and you want to be "playing" with your model data here and most of your data behavior to be handled here. I can't really dig in into this, others can do it better and there is a lot of ressources on the subject if you search for it (Search for example "Fat Model, Skinny Controller" in Google).
Now assuming you want the time left to be calculated every time you load the event page, you must specify it in your controller :
events_controller.rb :
def show
set_event
#time_left = #event.time_left
end
Then basically call #time_left in your view.

Answer 3

I'm not sure what #CaffeineCoder meant by "Put as much minimum logic in model , models are meant for only relationships", but along similar lines i would say:
Keep as much of your logic in your models as possible.
Models should hold all your business logic, controllers should do as little as possible, and views should handle anything which is to do with formatting data and presenting it to the user. Repeated bits of formatting can go in helpers, which is like a subsection of the View.
You don't tell us much about your schema so i can't advise on specifics, but you could for example have a method in Event like "time_remaining", which returns a number of seconds, and then have helpers which take this value and return "5d" or "4h" or whatever.