form_for but to post to a different action

I want to have a form_for @user, but post to a custom action in the users controller.

How can I do this?

form_for @user, :url => url_for(:controller => 'mycontroller', :action => 'myaction')

or

form_for @user, :url => whatever_path

The following works for me:

form_for @user, :url => {:action => "YourActionName"}

I have done it like that

<%= form_for :user, url: {action: "update", params: {id: @user.id}} do |f| %>

Note the optional parameter id set to user instance id attribute.

Alternatively the same can be reached using form_tag with the syntax:

form_tag({controller: "people", action: "search"}, method: "get", class: "nifty_form")
# => '<form accept-charset="UTF-8" action="/people/search" method="get" class="nifty_form">'

As described in http://guides.rubyonrails.org/form_helpers.html#multiple-hashes-in-form-helper-calls