Rails form helper: Multiple nested models like "Article.comments" in one form?

Question

Here is the form_with view-helper from the Rails "Getting Started" Guide (https://guides.rubyonrails.org/getting_started.html) for the nested Article model Comment or Article.comments:

<p>
  <strong>Title:</strong>
  <%= @article.title %>
</p>
 
<p>
  <strong>Text:</strong>
  <%= @article.text %>
</p>
 
<h2>Add a comment:</h2>
<%= form_with(model: [ @article, @article.comments.build ], local: true) do |form| %>
  <p>
    <%= form.label :commenter %><br>
    <%= form.text_field :commenter %>
  </p>
  <p>
    <%= form.label :body %><br>
    <%= form.text_area :body %>
  </p>
  <p>
    <%= form.submit %>
  </p>
<% end %>
 
<%= link_to 'Edit', edit_article_path(@article) %> |
<%= link_to 'Back', articles_path %>

Also

class Article < ApplicationRecord
  has_many :comments
  validates :title, presence: true,
                    length: { minimum: 5 }
end

and

class Comment < ApplicationRecord
  belongs_to :article
end

Now I would like to know if it is possible to use the form_with helper or another helper or helper-combination in order to create or edit a new Article with more than one nested models like Comment, Tag, ... and what further models an Article may be composed of.

... which creates a sane and useful params-Hash (because my own solution with a 'fields_for' form-helper doesn't produce a desired or useful params hash.

This is how the params-hash looks like:

<ActionController::Parameters {"utf8"=>"✓", "_method"=>"patch", "authenticity_token"=>"BeCtYS/U6lugXzzplTEBsMXAiD0x7z28iBUblHiza379p4YqRcd+ykgd49o53oOrC8o+iPhtWnvQQHe0ugCJow==", "article"=>{"parent_article_id"=>"", "title"=>"Überschrift", "text"=>"Toller Text"}, "tags"=>{"name"=>"Rails"}, "commit"=>"Update Article", "controller"=>"articles", "action"=>"update", "id"=>"1"} permitted: false>

The problem is that the controller/article id is not subsumed under the :article key. I don't know how to fix that for strong_parameters and I don't even want to. I would prefer Rails to just function after the principle of least astonishment instead of doing hackery things to get things working.

In this case I hope it's my own ignorance and lack of knowledge regarding form-helpers that prevents Rails from generating a proper params-hash.

Thanks.

Answer 1

Rails should be doing this as you expect. From accepts_nested_attributes:

Consider a member that has a number of posts:

class Member < ActiveRecord::Base
  has_many :posts
  accepts_nested_attributes_for :posts
end

You can now set or update attributes on the associated posts through an attribute hash for a member: include the key :posts_attributes with an array of hashes of post attributes as a value.

For each hash that does not have an id key a new record will be instantiated, unless the > hash also contains a _destroy key that evaluates to true.

params = { member: {
  name: 'joe', posts_attributes: [
    { title: 'Kari, the awesome Ruby documentation browser!' },
    { title: 'The egalitarian assumption of the modern citizen' },
    { title: '', _destroy: '1' } # this will be ignored
  ]
}}


member = Member.create(params[:member])
member.posts.length # => 2
member.posts.first.title # => 'Kari, the awesome Ruby documentation browser!'
member.posts.second.title # => 'The egalitarian assumption of the modern citizen'

The params hash you are showing is very strange. It looks like you're manually making disconnected fields like parent_article_id instead of actually using the capaibilities of form_with and fields_for.

I'd need to see your view and controller code to see how you've implemented form_with and fields_for to help you get these params nested the way you want.