How to debug undefined method form_with error

user_8590210 0
Viewed 5342

I'm getting the error:

undefined form_with for #<#<Class:0x7ac62e0>:0x551e5a8> in articles#new

The error occurs in the following file: new.html.erb Which has:

<%= form_with(model: [@article] , local: true) do |f| %>
  <p>
    <%= f.label :title %><enter code here`br>
    <%= f.text_field :title %>
  </p>

And the controller articles_controller.rb has:

class ArticlesController < ApplicationController
  def new
  end
end
ruby-on-rails
2 Answers

your controller just has new command see sample below for create instance variable @article

articles_controller.rb

class ArticlesController < ApplicationController 
  def new
    @article = Article.new
  end
end

new.html.erb

<%= form_with @article do |f| %>
  <%= f.label "Enter title: " %> 
  <%= f.text_field :title %> 
<% end %>
user_9389470

I've seen this error while working on nested routes. It occurred when the controller routes are defined as nested under another controller's route.

For example:

resources :authors do 
   resource :books, only: [index, :new]
end

it will create following routes:

/authors/author_id/books/:id
/authors/author_id/books/new

The method form_with try to execute the method book_path. But it is defined as author_books_path.

I found the solution by adding extra resources :books outside of the resources :books block.


resources :books

resources :authors do 
   resource :books, only: [:index, :new]
end

Edit: This solution will build the form without error but action URL won't be be correct because it will use books/.. instead of author/:author_id/books. That's why it is better use form_for instead of form_with while working on nested routes by passing parent and child model in a array.

<% form_for [@author, @book] do |form| %>
user_61111500
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