Ruby: return value or nil

Question

I have this method in Rails and it trips up when passed in parameter, date_string, is nil. Specifically when GetFileInfo -d returns nil.

What's a Rails-y way to handle this?

def calling_method
  ...
  m = MyModel.create(creation_date: cdate_for(path))
  ...
end

def cdate_for(path)
  local_datetime_for(`GetFileInfo -d "#{path}"`.chomp!)
end

def local_datetime_for(date_string)
  t = Time.strptime(date_string, '%m/%d/%Y %H:%M:%S') 
  DateTime.parse(t.to_s)
end

It's OK to return nil from this, assuming Model.create(creation_date: return_value_here) can handle nil values.

Edit: added some other methods to illustrate call chain.

Solution 1

You can use .blank?:

def local_datetime_for(date_string)
  return nil if date_string.blank?
  t = Time.strptime(date_string, '%m/%d/%Y %H:%M:%S') 
  DateTime.parse(t.to_s)
end

---

Some use cases for .blank?:

1.9.3p448 :042 > false.blank?
 => true 
1.9.3p448 :043 > true.blank?
 => false 
1.9.3p448 :044 > [].blank?
 => true 
1.9.3p448 :045 > ''.blank?
 => true 
1.9.3p448 :046 > '1'.blank?
 => false 
1.9.3p448 :047 > nil.blank?
 => true 

(For the record, .present? is the exact opposite of .blank?)

Solution 2

I think idiomatic Ruby calls for this:

def local_datetime_for(date_string)
  unless date_string.blank?
    t = Time.strptime(date_string, '%m/%d/%Y %H:%M:%S') 
    DateTime.parse(t.to_s)
  end
end

Or if you want to be fancy:

def local_datetime_for(date_string)
    DateTime.parse(Time.strptime(date_string, '%m/%d/%Y %H:%M:%S').to_s) unless date_string.blank?
end

Using return early in the method is very Ruby too. I just have trouble getting used to it coming from a Java background where I avoided early returns like the plague.

Solution 3

Use File.stat instead of calling out to the system for GetFileInfo. Then handle any exceptions with the stat in Ruby that might have caused a nil result.

def cdate_for(path)
  File.stat(path).ctime.to_datetime
end

Comments

[Meltemi]

added some other methods to illustrate the call chain. Trying to avoid wrapping things in if statements. Doesn't feel very "Rails-y"... perhaps I'm over thinking...

[RobertMcAtee]

@MrYoshiji 's answer using return nil if looks perhaps a little more "rubish". Also I know the code above is just a sample but just in case it is a copy of the code, I would recommend including "return"s