Question

I’m getting the following error in my rails app:

comparison of User with User failed

The relevant section of my controller looks like this:

class AssessmentsController < ApplicationController
  before_filter :authenticate_user!
  respond_to :html, :xml, :js, :pdf

def index
  @user = current_user
  @account = Account.find(@user.account_id)
  @assessments = Assessment.all
  respond_with @assessments
end

The relevant section of my view looks like this:

<%= form_for(@account) do |a| %>

<%= a.fields_for :users, @account.users.build do |u| %>

....
<%= a.submit "Sign-up", :class => "button", :disable_with => "Saving..." %>

<% end %>

<h1>Current users</h1>

<% for @user in @account.users.sort! { |b,a| a.id <=> b.id } %>
<%= render :partial => 'user' %>
<% end %>

The error seems to be originating around the for @user in @account.users.sort! section according to the error model, but removing it seems to be the addition of the @account.users.build in the fields_for section that creates it (but I need this as I want the user to be able to create a new user for that account. Can someone enlighten me to what is generating this?

Answer 1

The error is indeed occurring on that line, because ActiveRecord models don’t implement comparables by default. So when you say @account.users.sort!, the sort bombs out since it has no way to compare users with users.

There’s two things you can do here:

1. Implement the comparison operator for your user model. Check out this link for a blog post on how to do it, but it’d be something like:

   class User < ActiveRecord::Base
   
     def <=>(other)
       self.name <=> other.name
     end
   
   end
   

2. Tell the sort directly what comparison to use, like this:

   @account.users.sort! {|a, b| a.name <=> b.name}