Rails参数（url_params vs form_data）

Question

This is just a question out of curiosity.

Rails is magical in the way that it does a lot of things for us, but it comes with a curse of knowledge. When Rails receives an http request, we can access the inputs from client via params[]. However, I notice that params can accept inputs from both the url_params, and the form_data. For eg:

# Get  users/:id (param comes from url)
# Post users     (param comes from form)

Is there a rule to how params[] works? Will Rails just put all the parameters from url and form to params[]?

In the case of NodeJS, there is a distinction between

request.params
request.body
request.query

Answer 1

The answer can be found in the Rails Guides, in the chapter about Action Controller Overview -> Parameters :

Rails does not make any distinction between query string parameters and POST parameters, and both are available in the params hash in your controller:

Answer 2

What are params?

params are nothing but the parameters which are send to your controller when you send a HTTP request from your browser.

Types of params?

If you look at rail guides it says

There are two kinds of parameters possible in a web application. The first are parameters that are sent as part of the URL, called query string parameters. The query string is everything after "?" in the URL. The second type of parameter is usually referred to as POST data. This information usually comes from an HTML form which has been filled in by the user

Is there a rule to how params works?

As @zwippie pointed out rails doesn't make any distinction whether your params are coming from a form or a query string, but they do differ in the way rails put these params in a hash and hence different ways to access them in controller

For query string:

If your url is something like:

http://www.example.com/?vote[item_id]=1&vote[user_id]=2

then your params will look like:

{"item_id" => "1", "user_id" => "2"}

and hence you can access them in your controller by params[:item_id] and params[:user_id]

For POST data or from a form:

Lets say your form is like

<%= form_for @person do |f| %>
  <%= f.label :first_name %>:
  <%= f.text_field :first_name %><br />

  <%= f.label :last_name %>:
  <%= f.text_field :last_name %><br />

  <%= f.submit %>
<% end %>

and when you submit your form the parameters will look like this

{"person"=>   {"first_name"=>"xyz", "last_name"=>"abc"}}

notice how a form has nested your parameters in a hash so to access them in your controller you'll have to do params[:person] and to get individual values you can do params[:person][:first_name]