Rails 5.2.3 missing required keys: [:id] in new.html.erb form

Question

I am new to Ruby on Rails.

I have this controller:

class MynewsController < ApplicationController
    skip_before_action :authenticate_user!

    def new
    end

    def show
    end

    def create
        render plain: params[:mynew].inspect
    end
end

this row in routes.rb:

 resources :mynews

and this new.html.erb file:

<h1>New Mynews</h1>

<%= form_with scope: :mynew, local: true do |form| %>
    <p>
      <%= form.label :title %><br>
      <%= form.text_field :title %>
    </p>
   
    <p>
      <%= form.label :body %><br>
      <%= form.text_area :body %>
    </p>
   
    <p>
      <%= form.submit %>
    </p>
  <% end %>

It display the form and when i hit submit it displays the expected No route matches [POST] "/mynews/new" error

The problem is when i add the url parameter in the form_with row:

<%= form_with scope: :mynew, url: mynews_path, local: true do |form| %>

http://localhost:3000/mynews/new doesn't display the form and gives

No route matches {:action=>"show", :controller=>"mynews"}, missing required keys: [:id]

error.

I can't find what is the problem. Can you help me, please?

question from:https://stackoverflow.com/questions/66060464/rails-5-2-3-missing-required-keys-id-in-new-html-erb-form

Answer 1

Rather than using form_with scope: try this instead.

In your controller's new action you need to create a new unsaved record. I have no idea what your model is called, so I'm guessing based on your controller name:

def new
  @mynew = Mynew.new
end

Next, in your view, do the form like this:

<%= form_with model: @mynew, local: true do |form| %>

And it'll handle the paths etc for you.

However, I suspect your model probably isn't called Mynew, in which case you'd have to specify the url.

Assuming your model is actually called something like Article, I'd advise you to also name your controller ArticlesController. If you want the actual URL to be different you can configure that in your routes file ... but creating/updating/deleting an Article should be handled by the ArticlesController, regardless of what URL the users see.