How do I generate a field from other fields in rails model

Question

I have an address split up into @profile.street_address , @profile.region , @profile.zip_code .

I want to create

@profile.address = "#{@profile.street_address} #{@profile.region} #{@profile.zip_code}"

What is the best way to do this every time my model is created or updated?

Answer 1

You'll be best using the before_save to combine all the attributes into the one you want (although IMO this is bad practice):

#app/models/profile.rb
class Profile < ActiveRecord::Base
   before_save :set_address
   private

   def set_address
      self.address = "#{street_address} #{region} #{zip_code}"
   end
end

---

DRY

Something important to consider is the role of the DRY (Don't Repeat Yourself) principle within Rails, which means that you should only do something once, reusing it as often as required. This is extremely pertinent in the case of your data

To this end, I would highly recommend creating a custom getter for your address in your model:

#app/models/profile.rb
class Profile < ActiveRecord::Base
   def address
      "#{street_address} #{region} #{zip_code}"
   end
end

This will not save the address data to your database, but will give you the ability to load @profile.address in your controller & views. Why is this important? Simply, because when you call address , it will be pulling directly from the other attributes in your db, rather than the duplicated attribute you would have had otherwise

I would personally recommend this approach, but either will achieve what you want

Answer 2

You could set the before_save callback.

before_save do 
  self.address = "#{street_address} #{region} #{zip_code}"
end

Answer 3

In your address class:

before_save :set_address

def set_address
  self.address = "#{profile.street_address} #{profile.region} #{profile.zip_code}"
end

This assumes profile is available in your model.

It might be better to normalize your db by just making it an instance method, like this:

def address
  "#{profile.street_address} #{profile.region} #{profile.zip_code}"
end