I think I'm messing around ... Rails params

Question

I search a lot in those questions but I don't really see my problem and I hope I will ...

( I'm used to code in C, C++ etc... but I'm a newbie in rails ... )

I have a sign_up view and when I submit, rails automatically set every fields of the user that are filled in the form. It's cool but now I want to create a new text_field and take what the user enter as text in this text_field and uses it later without setting any other user's field, I have been told to use before_create and params or things like that but then I'm a noob ... In haml :

do |f|
  = f.text_field :email, :placeholder => "email"

works well (it set the email field with what the user enters)

do |f|
  = f.text_field NewVarThatIsNotAFieldOfCurrentNewUser, :placeholder => "referral code"

Then ofc, this error happens.

Error : undefined local variable or method `NewVarThatIsNotAFieldOfCurrentNewUser' (for the user class ofc)

If you want more information/code I'll edit this question :)

Thank you in advance !

Answer 1

Ruby / Rails is much simpler than C++

You don't need to "declare" new variables every time you want to use them - you just populate them in order to delcare them. Further, Ruby / Rails is object orientated, meaning that everything you do needs to be based around Objects.

---

Var

Your error is stated as such:

undefined local variable or method `NewVarThatIsNotAFieldOfCurrentNewUser'

What this means is that you're trying to load a variable which you have not created yet. I mentioned you don't need to declare variables in the same way as C++, but you do need to populate them with data, or at least have them accessible to your app

In order to do this, you'll need to declare & populate the variable in your controller, although this brings me onto my next point -- regarding the context in which you're trying to use the variable.

--

Objects

As Rails / Ruby is object-orientated, it means that everything you do needs to centre around objects. This is why your error states local variable or method -- objects have "methods" as well as data

Anyway, the way to fix your issue is to make sure that the attribute that your user has is available when you call / create the new User object. To do this, I would recommend using attr_accessor, although I'm not entirely sure what you're asking to be honest.

Here's what I'd do:

#app/models/user.rb
class User < ActiveRecord::Base
   attr_accessor :new_attribute
end

#app/views/users/sign_up.html.erb
<%= form_for @user do |f| %>
   <%= f.text_field :new_attribute %>
   <%= f.submit %>
<% end %>

This will create what's known as a virtual attribute, which means that it will not be saved into the database (as the database does not have the corresponding attribute supported)

---

Fix

If you wanted to collect data for a "new" attribute the user does not have data for (which is still in the database), you'll likely want to use the following:

#app/views/users/sign_up.html.erb
<%= form_for @user do |f| %>
   <%= f.text_field :attribute %>
   <% end %>
<% end %>

In regards to what you're asking - I believe the attr_accessor method is the most apt. This will give you the ability to "reuse" the data which is submitted without relying on storing it in the database.

--

MVC

Finally, to give you some more context - I don't know how familiar you are with MVC (I presume relatively), but I figured I give you some ideas on how Rails applications work:

MVC means that you have a Model, view and Controller. These all work together to provide a base level of functionality for your application - providing you with the capacity to create & edit data from your DB.

I mention this because if you can appreciate how Rails works from an architectural standpoint, you'll be in a much better position to make use of it. For example, you mention you're confused with before_create, and then tag the question with before_action.

These two callbacks serve different parts of the Rails framework, and will not, therefore, perform the same functionality.

-- before_create is for your Model

-- before_action is for your Controller