Check a condition before saving a nested object in Rails

Question

I have 3 model here : NewWord , VerbForm and AdjForm .

In NewWord model , I have a column word_type stored type of word: Adj Noun Verb Phrase GenericWord

Each NewWord may have 1 VerbForm or 1 AdjForm

Class NewWord < ApplicationRecord

    has_one :adj_form, dependent: :destroy
    has_one :verb_form, dependent: :destroy
    accepts_nested_attributes_for :adj_form, allow_destroy: true
    accepts_nested_attributes_for :verb_form, allow_destroy: true

   def self.types
        %w(Adj Noun Verb Phrase GenericWord)
   end
end

class NewWord::AdjForm < ApplicationRecord
    belongs_to :new_word
end

class NewWord::VerbForm < ApplicationRecord
    belongs_to :new_word
end

I use this form to create a word alongside with it forms

<%= simple_form_for new_word, remote: true do |f| %>
    <div class="error_section"></div>
    <%= f.input :word %>
    <%= f.input :kanji_version %>
    <%= f.input :word_type, collection: NewWord.types %>
    <%= f.simple_fields_for :verb_form do |v| %>
        <%= v.input :verb_type %>
        <%= v.input :dictionary_form %>
        # Other fields
    <% end %>
    <%= f.simple_fields_for :adj_form do |a| %>
        <%= a.input :adj_type %>
        # Other fields
    <% end %>
    <%= f.button :submit %>
<% end %>

My idea here is when user select word_type from dropdown, I can use Javasript to hide or show fields for AdjForm or VerbForm , or both. Then at submit, I only save AdjForm if new word's word_type is 'Adj', or VerbForm if word_type is 'Verb'.

So, how can I achieve this ? Since nested object saved automatically when I run this in new word create method: @new_word.save. ?

I have try reject_if but it only returns params for nested object only!

accepts_nested_attributes_for :adj_form, allow_destroy: true, reject_if: :not_adj

def not_adj(att)
    att['new_word']['word_type'] != 'Adj'   # Found out "att" here only has attributes of AdjForm , not NewWord !
end

Answer 1

In the controller, before saving, check the word_type value and discard the params that you dont want to save.

new_words_controller.rb

def create
  prepare_params     
  @new_word = NewWord.new(new_word_params)
  if @new_word.save
    # ...
  else
    # ...
  end
end

private
def prepare_params
  params.delete[:verb_form] if params[:word_type] == "Adj"
  params.delete[:adj_form] if params[:word_type] == "Verb"
  params
end

This assumes you have whitelisted the parameters for new_word and its associations.