c# barcode generator library free <h1><%= link_to entry.title, :action => 'show', :id => entry.id %></h1> in Font

Creator Data Matrix in Font <h1><%= link_to entry.title, :action => 'show', :id => entry.id %></h1>

This line creates a heading that contains a link to the show action for that entry and would render into final HTML like this:

If you were to click the link, you would be redirected to the show action for the entries controller, and an ID of 1 would be passed through. Let s look at what the show action does with this:

The show action is simple, as all it does is retrieve a single entry from the database (using, as always, the find method provided by the Entry model from ActiveRecord::Base). You retrieve the ID from the URL through the params hash, a hash that is automatically populated by any data passed to the Rails application via the URL. If you use find with a single parameter containing an integer ID, then that row will be retrieved from the relevant table for the associated model, and returned as a single object. In this case, the entry retrieved is associated with @entry, then the view at app/views/entries/show.rhtml renders the page you see. Here are some examples of how some URLs relate to parameters that are found in the params hash:

http://localhost/entries/show/1

params[:controller] == 'entries' params[:action] == 'show' params[:id] == '1'

params[:controller] == 'entries' params[:action] == 'another_method' params[:id] == '20' params[:formfield1] == 'test' params[:formfield2] == 'hello'

params[:controller] == 'test' params[:action] == 'test2' params[:formfield1] == 'test' params[:formfield2] == 'hello'

These examples demonstrate how you can pass data into methods within the URL (or, in the case of POST requests such as those that can be made from an HTML form within the HTTP request directly) and then access it by the controllers (or views) through the params hash. If you look at the code for the create action an action used to create the new entries as supplied by the form at http://localhost/entries/new you ll see how params is used to create new entries:

def create @entry = Entry.new(params[:entry]) if @entry.save flash[:notice] = 'Entry was successfully created.' redirect_to :action => 'list' else render :action => 'new' end end

In this method, you create a new entry with Entry.new(params[:entry]). The new method provided by ActiveRecord accepts the entire params hash and makes a new row of data from it. On the next line you save that row to the database using @entry.save, which returns true or false. If true (that is, the attempt is successful), the user will be redirected to the list action (try changing this to view_all). If the save isn t successful, the view for the new action is rendered using render :action => 'new'. Note how you can use redirect_to and render to perform operations that don t necessarily fit in with the usual controller action view life cycle, such as redirecting users elsewhere or rendering views associated with other controller actions.

This section has covered only the basics of using controllers and views, but these are the most essential parts to learn. Other features provided by views and controllers rely on the concepts covered in this section. URLs are parsed into the desired controller and action, any other supplied data is passed through the action via the params hash, and once the action code has completed, a view is rendered. In the next section you ll take a look at how you can customize the URL parsing system so that URLs of your own formatting can be converted into any controller and method patterns that you wish. This technique is known as routing.

When you request a page from a Rails application that isn t present within the public folder, the Rails application tries to work out which controller and action you are trying to use. In the previous sections, you ve seen how a URL such as http://localhost/ entries/view_all means that the request is put through to the entries controller s view_all action. You can use routing to override this default assumption that all URLs are of the form controller_name/action_name/id. Routing configurations for a Rails application are located in config/routes.rb. Let s look at what ours contains by default:

ActionController::Routing::Routes.draw do |map| # The priority is based upon order of creation: first created -> highest priority # Sample of regular route: # map.connect 'products/:id', :controller => 'catalog', :action => 'view' # Keep in mind you can assign values other than :controller and :action