Processing of Requests

In the previous lesson, we worked out how Action Dispatch routes an incoming request to the appropriate code in your application. Now let’s see what happens inside that code.

Action methods

When a controller object processes a request, it looks for a public instance method with the same name as the incoming action. If it finds one, that method is invoked. If it doesn’t find one and the controller implements method_missing(), that method is called, passing in the action name as the first parameter and an empty argument list as the second. If no method can be called, the controller looks for a template named after the current controller and action. If found, this template is rendered directly. If none of these things happens, an AbstractController::ActionNotFound error is generated.

Controller environment

The controller sets up the environment for actions (and, by extension, for the views that they invoke). Many of these methods provide direct access to the information contained in the URL or request:

• action_name

  The name of the action currently being processed.

• cookies

  The cookies are associated with the request. Setting values into this object stores cookies on the browser when the response is sent. Rails support for sessions is based on cookies.

• headers

  A hash of HTTP headers will be used in the response. By default, Cache-Control is set to no-cache. We might want to set Content-Type headers for special-purpose applications. Note that we shouldn’t set cookie values in the header directly. Use the cookie API to do this.

• params

  A hash-like object containing request parameters along with pseudo parameters generated during routing. It’s hash-like because we can index entries using either a symbol or a string. The params[:id] and params['id'] return the same value. Idiomatic Rails applications use the symbol form.

• request

  The incoming request object. It includes these attributes:

  • The request_method attribute returns the request method, one of :delete, :get, :head, :post, or :put.

  • The method attribute returns the same value as request_method except for :head, which it returns as :get because these two are functionally equivalent from an application’s point of view.

  • The delete?, get?, head?, post?, and put? attribute return true or false based on the request method.

  • The xml_http_request? and xhr? attribute return true if this request was issued by one of the Ajax helpers. Note that this parameter is independent of the method parameter.

  • The url() attribute, which returns the full URL used for the request.

  • The protocol(),host(),port(),path(), and query_string()attribute, which return components of the URL used for the request based on the following pattern: protocol://host:port/path?query_string.

  • The domain()attribute, which returns the last two components of the domain name of the request.

  • The host_with_port()attribute, which is a host:port string for the request.

  • The port_string() ...