I am an newbie. I have read the API documentation. But still don't understand how form_for works.
Firstly, from Ruby on Rails Tutorial, the form for follow button:
<%= form_for(current_user.relationships.build(followed_id: @user.id)) do |f| %>
<div><%= f.hidden_field :followed_id %></div>
<%= f.submit "Follow", class: "btn btn-large btn-primary" %>
<% end %>
I understand current_user.relationships.build(followed_id: @user.id) means a new record. But why can we not just submit and trigger controller to save the record without hidden_field? Why do we still need to post followed_id to controller?
Secondly, in hidden_field, what does :followed_id means? I believe that is a symbol, i.e. it equals only "followed_id" not a variable of id. If that is only the name of the input field, then what is its value?
Thirdly, how does form_for know where the submission should be sent to? Which controller and action the form_for will post to?
Fourth, how does params work with form_for? In this follow button case, params[:relationship][:followed_id] will return @user.id in controller. How does it know the first hash attribute is :relationship? We have neither mentioned form_for :relationship nor form_for @relationship.
I know these questions can be very dumb, but I am really stuck. Any help will be appreciated.