Rails fields_for non-nested models

Objects

I understand what you want - still trying to consider how to get it working.

Something you need to consider is the nature of Ruby on Rails (Ruby in particular). Ruby is an object orientated language, meaning everything it does is based around objects.

The problem you have is the object you're trying to create ("RoadBlockHistories") has no direct association to your "parent" object that you're trying to create ("HabitJournals").

accepts_nested_attributes_for

The "way" you'd surmount this problem typically is to use the accepts_nested_attributes_for method - basically allowing you to pass data from a parent model to a child.

The important thing to note here is that this only works if your models are directly associated, IE that it's either a has_many, belongs_to or has_many :through for the model you're trying to create.

This is not magic - it's core Ruby. If you have a model you're trying to populate, if it has associated data, you'll be able to send that through your original model. However, as the language is object orientated, you cannot just populate an unrelated object without having that association

Fix

From what you've written, I would certainly look at treating the two forms as separate data objects (IE not associating them)

Perhaps you could do this (although it will need tweaking):

#app/models/habit.rb
class Habit < ActiveRecord::Base
  has_many :habit_journals
  has_many :road_blocks
end

#app/models/road_block.rb
class RoadBlock < ActiveRecord::Base
  belongs_to :habit
  has_many :road_block_histories
end

#app/models/habit_journal.rb
class HabitJournal < ActiveRecord::Base
   belongs_to :habit
   has_many :road_blocks
end

Although this is not tested, nor do I think it would work, the reason I included this is to give you the idea about how you could pass an "unassociated" object through to Rails.

You can actually pass objects / data through others - so you could actually use something like the following:

#app/controllers/habit_journals_controller.rb
Class HabitJournalsController < ApplicationController
   def new
       @habit_journal = HabitJournal.new
       @habit_journal.road_blocks.build.road_block_histories.build #-> again, not sure if will work
   end

   def create
       @habit_journal = HabitJournal.new(habit_journal_params)
       @habit_journal.save
   end

   private

   def habit_journal_params 
       params.require(:habit_journal).permit(:x, :y, :z, road_blocks_attributes: [road_block_histories_attributes:[] ])
   end
end

If the associations are correct, this should allow you to create the following form:

#app/views/habit_jorunals/new.html.erb
<%= form_for @habit_journal do |f| %>
   <%= f.fields_for :road_blocks do |rb| %>
       <%= rb.fields_for :road_blocks_histories do |h| %>
           <%= h.text_field :rating %>
       <% end %>
   <% end %>
<% end %>