Get current_user in Rails form validation by defining a virtual attribute

Question

Rails form validation is designed to go in the model most easily. But I need to make sure the current user has the required privileges to submit a post and the current_user variable is only accessible in the controller and view.

I found this answer in a similar question:

You could define a :user_gold virtual attribute for Book, set it in the controller where you have access to current_user and then incorporate that into your Book validation.`

How can I set this up with my post and user controller so that the current_user variable is accessible in the model?

Solution:

This whole thing is wrong from an application design perspective as @Deefour's answer pointed out. I changed it so my view doesn't render the form unless the condition is true.

Answer 1

The "similar question" is saying you can do something like this

class YourModel < ActiveRecord::Base
  attr_accessor :current_user

  # ...
end

and then in your controller action you can do something like

@your_model = YourModel.find(params[:id])
@your_model.current_user = current_user
@your_model.assign_attributes(params[:your_model])

if @your_model.valid?
  # ...

You can then use self.current_user within YourModel's validation methods.

---

Note I don't think this is what you should be doing though, as I don't consider this "validation" as much as "authorization". An unauthorized user shouldn't even be able to get the part of your action where such an update to a YourModel instance could be saved.

---

As for doing the authorization with Pundit as requested, you'd have a file in app/policies/your_model.rb

class YourModelPolicy < Struct.new(:user, :your_model)
  def update?
    user.some_privilege == true # change this to suit your needs, checking the "required privileges" you mention
  end
end

Include Pundit in your ApplicationController

class ApplicationController < ActionController::Base
  include Pundit
  # ...
end

Then, in your controller action you can do simply

def update
  @your_model = YourModel.find(params[:id])
  authorize @your_model

  # ...

The authorize method will call YourModelPolicy's update? method (it calls the method matching your action + ? by default) and if a falsy value is returned a 403 error will result.