Rails generates a form partial that can be used on both the page rendered by a get action and a page rendered by a new action. If it is the former the form's method is set to PUT, if the latter the form's action is set to POST.
How does rails decide which method to use?
Both GET and POST hold intrinsic meaning if you're making an HTML-based API. But in general, GET is used for fetching data, POST is used for submitting data. The biggest difference is that GET puts all the data in the URL (which can be limited in size), while POST sends it as a data part of the HTTP request.
What's rendering in Rails? Rendering is the ultimate goal of your Ruby on Rails application. You render a view, usually . html. erb files, which contain a mix of HMTL & Ruby code.
if the object passed to the form is persisted?
, the form builder knows that you are updating an object and will therefore render a PUT
action. If it is not persisted, then it knows you are creating a new object and it will use POST
.
<%= form_for @user do |f| %>
<%= f.button %>
<% end %>
If @user
is a new record, POST
is used and the button label becomes Create User
, otherwise PUT
is used and the label becomes Update User
. There's not much more to it.
Forms editing existing resources use PUT
, forms creating a new resource use POST
. As per REST standards described here.
From the rails form_for
helper code:
action, method = object.respond_to?(:persisted?) && object.persisted? ? [:edit, :put] : [:new, :post]
and persisted?
for ActiveRecord is declared as:
!(new_record? || destroyed?)
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