Rolling with Ruby on Rails - Part 2.pdf - RUBY Programming - Ryjufka

Published on ONLamp.com ( http://www.onlamp.com/ )

http://www.onlamp.com/pub/a/onlamp/2005/03/03/rails.html

See this if you're having trouble printing code examples

Rolling with Ruby on Rails, Part 2

by Curt Hibbs

03/03/2005

Welcome back!

In Rolling with Ruby on Rails , I barely scratched the surface of what you can do with Ruby on Rails. I didn't talk about data

validation or database transactions, and I did not mention callbacks, unit testing, or caching. There was hardly a mention of

the many helpers that Rails includes to make your life easier. I can't really do justice to all of these topics in the space of this

article, but I will go into details on some of them and present a brief overview of the rest, with links to more detailed

information.

Also, I purposely did not go into any detail about the Ruby programming language. If you are interested in a brief treatment

of the whys behind the Ruby and Rails code that you saw in Part 1, then I highly recommend reading Amy Hoy's blog entry

Really Getting Started in Rails .

Before I cover this stuff, I want to complete the homework items from the end of Part 1:

There is no longer any way to delete a recipe. Add a delete button (or link) to the edit template.

On the main recipes page, there aren't any links for the pages that let you manipulate categories. Fix that.

It would be nice to have a way to display only those recipes in a particular category. For example, maybe I'd like to see

a list of all snack recipes, or all beverage recipes. On the page that lists all recipes, make each category name a link to

a page that will display all of the recipes in that category.

One alert reader pointed out that after adding categories, it was no longer possible to add any new recipes because the new

recipe action (as provided by the scaffolding) had no way to assign a category, and this caused the list recipes action to

produce an error. This also needs fixing.

Are you ready? Let's begin!

Updating Ruby on Rails

When I wrote Part 1 , the current version of Rails was 0.9.3. At the time of this writing, Rails is up to version 0.10.0 and has

some useful new features. I will use Rails 0.10.0 for this article. If you installed Rails after February 24, 2005, you already

have 0.10.0 installed.

Figure 1 shows how to see what RubyGems you have installed (and their version numbers). As with Part 1, I am working on

a Windows system, so you will need to translate if you use a different platform.

Figure 1. Listing installed RubyGems

Open a command window and run the command:

gem list --local

Tip: the command gem list --remote will show all the available RubyGems on the remote gem server on

rubyforge.org .

If you don't have Rails 0.10.0 (or later) installed, then you will need to rerun the command:

gem install rails

MySQL security update

In Part 1, I recommended that you leave the MySQL root password blank because (at the time of writing) Rails did not

support MySQL's new password protocol. Many of you were not happy with this state of affairs, and to make matters worse,

there is now a virus that exploits password vulnerabilities in MySQL on Windows.

Happily, starting with version 0.9.4, Rails now supports the new password protocol.

New scaffold feature

Rails has a new scaffold feature, which I won't explore here, but it's cool enough that I want to make sure you know about it.

This is best illustrated by an example.

Part 1 showed how to create a recipe model and controller with the commands:

ruby script\generate model Recipe

ruby script\generate controller Recipe

I then instantiated the scaffolding by inserting scaffold :recipe into the RecipeController class. The resulting

CRUD controllers and view templates were created on the fly and are not visible for inspection.

The technique described above still works, but you now have another option. Run the command:

ruby script\generate scaffold Recipe

This generates both the model and the controller, plus it creates scaffold code and view templates for all CRUD operations.

This allows you to see the scaffold code and modify it to meet your needs. Be careful using this if you've already created

models, controllers, or view templates, as it will overwrite any existing files as it creates the scaffold code.

Completing the Recipe Application

It's time to round out the recipe application a bit. After that I'll present some other features of Rails that I'm sure you'll want

to know about.

Remember that I created my cookbook application in the directory c:\rails\cookbook ; all paths used in this article assume

this base directory. If you chose a different location, please be sure to make the proper adjustments to the application paths

you see in this article.

If you completed Part 1 using anything earlier than Rails 0.10.0, you will need to update your cookbook application to work

with Rails 0.10.0. You can either follow the upgrading instructions or download my cookbook source code , which has the

upgrades already.

For those of you who are cheating (you know who you are) and plan to just download my source code without going through

Part 1, you will also need to create a database named cookbook in MySQL and populate it using cookbook.sql .

Creating a new recipe with a category

Because the code still relies on the scaffolding to create new recipes, there is no way to assign a category to a recipe. This

wouldn't be so bad--except that the page created to list all recipes assumes that every recipe will have a category, and it

generates an error if this is not true. That means that in the way I left things in Part 1, if you add a new recipe, you'll receive

errors while trying to list them.

The fix is to take over the new action from the scaffolding just as I showed already with the edit action. Edit

c:\rails\cookbook\app\controllers\recipe_controller.rb and add a new method like in Figure 2.

Figure 2. The Recipe controller's new method

The code @recipe = Recipe.new creates a new, empty recipe object and assigns it to the instance variable @recipe .

Remember, an instance of the Recipe class represents a row in the recipes database table. When creating a new recipe

object, the Recipe class can assign default values for each field that the view template can use.

The Recipe model class doesn't currently set any such default values, but the view template I'll show off momentarily will

use whatever is in the @recipe object to initialize the display form. Later, you could add default values in the Recipe class

that will show up when you create a new recipe.

As with the edit action, this also retrieves a collection of all categories so that it can display a drop-down list of categories

from which the user can choose. The @categories instance variable holds this list of categories.

In the directory c:\rails\cookbook\app\views\recipe , create a file named new.rhtml that contains the HTML template shown

below. It's mostly standard HTML, with some extra code to create the <select> and <option> tags for the drop-down

list of categories:

<html>

<head>

<title>New Recipe</title>

</head>

<body>

<h1>New Recipe</h1>

<p>

<b>Title</b><br/>

</p>

<p>

<b>Description</b><br/>

<input id="recipe_description" name="recipe[description]"

size="30" type="text" value=""/>

</p>

<p>

<b>Category:</b><br/>

<% @categories.each do |category| %>

<%= category.name %>

</option>

<% end %>

</select>

</p>

<p>

<b>Instructions</b><br/>

<textarea cols="40" id="recipe_instructions" name="recipe[instructions]"

rows="20" wrap="virtual">

</textarea>

</p>

</form>

</body>

</html>

This is not much different from the edit template from Part 1. I left out the recipe's date because I'll set it to the current date

when a user posts the form back to the web app. This ensures that the recipe's date will always be its creation date.

If you look at the form tag, you will see that this form will post to a create action in the recipe controller. Edit

c:\rails\cookbook\app\controllers\recipe_controller.rb and add this create method:

def create

@recipe = Recipe.new(@params['recipe'])

@recipe.date = Date.today

if @recipe.save

redirect_to :action => 'list'

else

render_action 'new'

end

This method first creates a new recipe object and initializes it from the parameters posted by the form in new.rhtml . Then it

sets the recipe's date to today's date, and tells the recipe object to save itself to the database. If the save is successful, it

redirects to the list action that displays all recipes. If the save fails, it redirects back to the new action so the user can try

again.

Give it a try. Start the web server by opening a command window, navigating to c:\rails\cookbook , and running the

command ruby script\server . Then browse to http://127.0.0.1:3000/recipe/new and add a new recipe

like the one shown in Figure 3.

Figure 3. Adding a new recipe with a category

After you create the new recipe, you should see something like Figure 4.

Figure 4. List of all recipes

Deleting a recipe

If you remember from Part 1, once I took over the list action from the scaffolding I no longer had a way to delete a recipe.

Rolling with Ruby on Rails - Part 2.pdf

Plik z chomika:

Inne pliki z tego folderu:

Inne foldery tego chomika: