Ruby on Rails: Are “form_for(:product, …)” and “form_for(@product, …)” equivalent?

Question

Is

<%= form_for(:product, :url => {:action => \'update\', :id => @product.id})) do |f| %>
  ...
<% end %>

and

<         


        

Answer 1

Similar, but not the same. When you use @product you have the benefit of being able to automatically populate values to the form fields from the model instance.

For example, if you in the action :new in your Controller assign @product like this:

@product = Product.new

Then there will probably not be any difference in the generated form. However, if you follow this up in you :create action like this:

@product = Product.new(params[:product])
if @product.save
  ...
else
  render :action => :new
end

Then if it is unable to save the @product instance, then it will render the same form as in :new but this time have all the fields populated with the values posted. That would not have been possible if you used :product