form_for Ruby On Rails - ruby-on-rails

Question

I'm trying to follow a tutorial on using basic AJAX to add a record to a list in place, and I'm having issues using form form_for.
Here is my code.
<%= form_for ([#product, #product.new]) do |p| %>
<p>
<%= p.label :product_part %>
<%= p.text_field :product_part%>
</p>
<p>
<%= p.submit %>
</p>
<% end %>
The error I am getting is
undefined method `new' for nil:NilClass
I understand why I am getting the error (#products hasn't been "initialized") but I have no idea how to fix this issue (I am sure it's simple). I have seen something about putting a resource in the routes file, but I do not know for sure.

Answer 1

If you're trying to make a form for a new product, you should (in your controller) be setting #product to an instance of a new Product:
# app/controllers/products_controller.rb
def new
#product = Product.new
end
In your view, using [#product, #product.new] makes no sense. You can't invoke new on an instance of a product. It's very unclear why you're not simply using the following, which is the correct use of form_for with a new instance of an ActiveRecord model:
form_for #product do |p|

Answer 2

Do this:
#app/controllers/products_controller.rb
class ProductsController < ApplicationController
def new
#product = Product.new
render :form
end
def edit
#product = Product.find params[:id]
render :form
end
end
#app/views/products/form.html.erb
<%= form_for #product, remote: true do |f| %>
<%= p.label :product_part %>
<%= p.text_field :product_part%>
<%= f.submit %>
<% end %>
This will do everything you need for both the new and edit methods (which you raised concerns about in your comments with #meagar).
This should be corroborated with the following routes (you can see why here):
#config/routes.rb
resources :products

Answer 3

I would say In case you need to look the form_for helper ; to understand the behavior of the method.
The method form_for It accept the argument as record, options = {}. The value of record could be a symbol object or a newly object of respective class in your case Person.new.
Second argument could be
:url, :namespace, :method, :authenticity_token, :remote , :enforce_utf8, :html
Among them :remote => true option is used as the Ajaxify your request.
form_for is a helper that assists with writing forms. form_for takes a :remote option. It works like this:
<%= form_for(#article, remote: true) do |f| %>
....
<% end %>
This will generate the following HTML:
<form accept-charset="UTF-8" action="/articles" class="new_article" data-remote="true" id="new_article" method="post">
...
</form>
Note the data-remote="true". Now, the form will be submitted by Ajax rather than by the browser's normal submit mechanism.
For more info about Form-For helper
Hope this solve your problem!!!.