What is the difference between this:

controller

@user = User.new

@order = Order.new

view:

<%= form_for :user do |user| %>
    ...
    ...
    <%= fields_for :order do |order| %>
    ...
    ...
    <% end %>
<% end %>

I can extract the values in the params-object like this params[:us开发者_如何转开发er] and params[:order]

But I could also have written:

<%= form_for :user do |user| %>
    ...
    ...
    <%= user.fields_for :order do |order| %>
    ...
    ...
    <% end %>
<% end %>

and I could have extracted the values in the params-object like this params[:user][:order].

Is the equal, distinguished by the way I extract values from?

Generally you would use the nested version of fields_for if you were using this line in your User model:

has_many :orders
accepts_nested_attributes_for :orders

By defining this, you will be able to create a new user and new order record*s* at the same time by using this in the create action of your UsersController:

@user = User.new(params[:user])

Because you're using accepts_nested_attributes_for now, the order attributes will be passed through as params[:user][:orders_attributes].