The Users Resource in Java

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The Users Resource
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The page to show a user (/users/1)
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Now we ll create a second user by revisiting the new page and submitting a second set of user information; the resulting user index is shown in Figure 29 Section 103 will develop the user index into a more polished page for showing all users Having shown how to create, show, and edit users, we come finally to destroying them (Figure 210, page 54) You should verify that clicking on the link in Figure 210 destroys the second user, yielding an index page with only one user (If it doesn t work, be sure that JavaScript is enabled in your browser; Rails uses JavaScript to issue the request needed to destroy a user) Section 104 adds user deletion to the sample app, taking care to restrict its use to a special class of administrative users
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222 MVC in Action
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Now that we ve completed a quick overview of the Users resource, let s examine one particular part of it in the context of the Model-View-Controller (MVC) pattern introduced
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2: A Demo App
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The user edit page (/users/1/edit)
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in Section 126 Our strategy will be to describe the results of a typical browser hit a visit to the user index page at /users in terms of MVC (Figure 211, page 55) The steps in Figure 211: 1 2 3 4 5 6 The browser issues a request for the /users URL Rails routes /users to the index action in the Users controller The index action asks the User model to retrieve all users (Userall) The User model pulls all the users from the database The User model returns the list of users to the controller The controller captures the users in the @users variable, which is passed to the index view
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The Users Resource
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A user with updated information
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7 The view uses Embedded Ruby to render the page as HTML 8 The controller passes the HTML back to the browser7 We start with a request issued from the browser ie, the result of typing a URL in the address bar or clicking on a link (Step 1 in Figure 211) This request hits the Rails router (Step 2), which dispatches to the proper controller action based on the URL (and, as we ll see in Box 31, the type of request) The code to create the mapping of user URLs to controller actions for the Users resource appears in Listing 22;8 this code effectively sets up the table of URL/action pairs seen in Table 21
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7 Some references indicate that the view returns the HTML directly to the browser (via a web server such as Apache or Nginx) Regardless of the implementation details, I prefer to think of the controller as a central hub through which all the application s information flows 8 The strange notation :users is a symbol, which we ll learn about in Section 433
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The user index page (/users) with a second user
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Listing 22 The Rails routes, with a rule for the Users resource
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config/routesrb
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DemoApp::Applicationroutesdraw do resources :users end
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The pages from the tour in Section 221 correspond to actions in the Users controller, which is a collection of related actions; the controller generated by the scaffolding is shown schematically in Listing 23 Note the notation class UsersController < ApplicationController; this is an example of a Ruby class with inheritance (We ll discuss inheritance briefly in Section 234 and cover both subjects in more detail in Section 44)
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The Users Resource
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Listing 23 The Users controller in schematic form
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app/controllers/users_controllerrb
class UsersController < ApplicationController def index end def show end def new end def create end def edit end def update end def destroy end end
2: A Demo App
Destroying a user
You may notice that there are more actions than there are pages; the index, show, new, and edit actions all correspond to pages from Section 221, but there are additional create, update, and destroy actions as well These actions don t typically render pages (although they sometimes do); instead, their main purpose is to modify information about users in the database This full suite of controller actions, summarized in Table 22, represents the implementation of the REST architecture in Rails (Box 22) Note from Table 22 that there is some overlap in the URLs; for example, both the user show action and the update action correspond to the URL /users/1 The difference between them is the HTTP request method they respond to We ll learn more about HTTP request methods starting in Section 322
Box 22 REpresentational State Transfer (REST)
If you read much about Ruby on Rails web development, you ll see a lot of references to REST , which is an acronym for REpresentational State Transfer REST is an