Question

When I go to new_heuristic_variant_cycle_path, my app displays the new view for cycle, but the submit button on the form says “Update Cycle” not “Create Cycle”, and when you click the submit button the controller goes looking for an update action. Why?

I have…

/config/routes.rb:

Testivate::Application.routes.draw do
  resources :heuristics do
    resources :variants do
      resources :cycles
    end
  end
end

/app/models/heuristics.rb:

class Heuristic < ActiveRecord::Base
  has_many :variants
  has_many :cycles, :through => :variants
end

/app/models/variants.rb:

class Variant < ActiveRecord::Base
  belongs_to :heuristic
  has_many :cycles
end

/app/models/cycles.rb:

class Cycle < ActiveRecord::Base
  belongs_to :variant
end

/app/views/cycles/new.html.haml:

%h1 New Cycle
= render 'form'

/app/views/cycles/_form.html.haml:

= simple_form_for [@heuristic, @variant, @cycle] do |f|
  = f.button :submit

/app/controllers/cycles_controller.rb:

class CyclesController < ApplicationController
  def new
    @heuristic = Heuristic.find(params[:heuristic_id])
    @variant = @heuristic.variants.find(params[:variant_id])
    @cycle = @variant.cycles.create
    respond_to do |format|
      format.html # new.html.erb
    end
  end
  def create
    @heuristic = Heuristic.find(params[:heuristic_id])
    @variant = @heuristic.variants.find(params[:variant_id])
    @cycle = @variant.cycles.create(params[:cycle])
    respond_to do |format|
      if @cycle.save
        format.html { redirect_to heuristic_variant_cycles_path(@heuristic, @variant, @cycle), notice: 'Cycle was successfully created.' }
      else
        format.html { render action: "new" }
      end
    end
  end
end

Answer 1

In your controller, this line of code is wrong:

@cycle = @variant.cycles.create

It should be this:

@cycle = @variant.cycles.build

When you call create, the record is saved. In the doc:

collection.build(attributes = {}, …)

Returns one or more new objects of the collection type that have been instantiated with attributes and linked to this object through a foreign key, but have not yet been saved.

collection.create(attributes = {})

Returns a new object of the collection type that has been instantiated with attributes, linked to this object through a foreign key, and that has already been saved (if it passed the validation). Note: This only works if the base model already exists in the DB, not if it is a new (unsaved) record!