You will probably want to access data sent in by the user or other parameters in your controller actions.
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Rails does not make any distinction between query string parameters and POST parameters, and both are available in the params hash in your controller:
paramsはhashににており、controllerで使用する。
To send a hash you include the key name inside the brackets:
<form accept-charset="UTF-8" action="/clients" method="post">
<input type="text" name="client[name]" value="Acme" />
<input type="text" name="client[phone]" value="12345" />
<input type="text" name="client[address][postcode]" value="12345" />
<input type="text" name="client[address][city]" value="Carrot City" />
</form>
When this form is submitted, the value of params[:client] will be { "name" => "Acme", "phone" => "12345", "address" => { "postcode" => "12345", "city" => "Carrot City" } }. Note the nested hash in params[:client][:address].
Note that the params hash is actually an instance of ActiveSupport::HashWithIndifferentAccess, which acts like a hash but lets you use symbols and strings interchangeably as keys.
このようにnestしたhashをつくれる。また実態はActiveSupport::HashWithIndifferentAccess。
4.3 Routing Parameters
The params hash will always contain the :controller and :action keys, but you should use the methods controller_name and action_name instead to access these values. Any other parameters defined by the routing, such as :id will also be available. As an example, consider a listing of clients where the list can show either active or inactive clients. We can add a route which captures the :status parameter in a "pretty" URL:
get '/clients/:status' => 'clients#index', foo: 'bar'
In this case, when a user opens the URL /clients/active, params[:status] will be set to "active". When this route is used, params[:foo] will also be set to "bar" just like it was passed in the query string. In the same way params[:action] will contain "index".
params[:controller]とparams[:action]が利用できるけど、controller_nameとaction_nameを使用するほうがよい。
また:statusのようにrouteでparamsを設定することもできる。