yeah dev: The Ultimate introduction to Merb

Hello Merb

Why Merb?

Merb is a Mode-View-Controller (MVC) web-based framework that takes a slightly different different approach to web development compared to that other Ruby web framework, Ruby On Rails. With Merb you can choose your ORM (DataMapper, Sequel and ActiveRecord), template engine (Haml or eRuby).

From Install to "Hello World"

Install Merb and it's dependencies
To install Merb, all you need to run is
```
sudo gem install merb --include-dependencies
```
Generate your Merb application
To generate a your Merb app's folder (in this case, we'll call our app "merbtest"), all you need to run is
```
merb-gen app merbtest
```
This will generate all of the base files and folders for your Merb app.
Fire your app up
Technically, at this point you can fire your app by just running
```
merb
```
from your app's root. By default, you'll be able to access your app at http://localhost:4000. You will get the default "Welcome to Merb" page which also tells us, amongst other things, how to get rid of this page (This page also happens to be the 404 page. You can view it in the app/views/exceptions folder).
Setup your routes
Your route configuration will take place in the config/router.rb file. Like Rails, you get the default route of ":controller/:action/:id" which is fine unless you have a number of "resource" routes and you want to prevent GET requests from hitting your create and destroy methods (or any other method you want to be only accessible via POST). For the purpose of this introduction to Merb, let's set a specific route for our controller we have yet to create. Comment out the r.default_routes and add this route:
```
 r.match('/hello').to(:controller => 'hello', :action => 'show') 
```
. This will map any requests sent to localhost:4000/hello to the hello controller's show method. I guess we should go create that controller.
Creating Controllers
To create the "Hello" controller, run
```
merb-gen controller hello --testing-framework rspec 
```
Telling the generator what testing framework you're using lets merb generate the related test files which in our case would be a spec file for our controller and helper we just created. Run
```
merb-gen controller
```
if you'd like to see the other optional flags.

Now that we have a controller, all we need to do is define our show method and create the associated view template. Add this to your Hello controller
```
def show
@hello = 'hi'
render
end 
```
and this to your app/views/hello/show.html.erb file:
```
 say <%= @hello >  
```
and that's it.

Setting up your ORM
As far as ORM's go, I've been wanting to try Sequel, so let's run with that. to install it, run:
```
sudo gem install merb_sequel
```
and in your config/init.rb add or uncomment
```
use_orm :sequel
```
Now we have Sequel ready and willing. Run merb in your app root to have Sequel create a sample database.yml in your config folder you can copy from. Your database.yml file will need to look something like this:
```
:development: &defaults
  :adapter: mysql
  :database: merbtest_development
  :username: root
  :password:
  :host: localhost

:test:
  <<: *defaults   :database: merbtest_test  
:production:   
  <<: *defaults   :database: merbtest_production 
```

To actually populate the database we'll need a model and an actual migration to set our table up. Let's start with the model. Run


merb-gen model book


merb-gen migration add_books_table --orm sequel


class AddBooksTable < Sequel::Migration
  def up
    create_table :books do
      primary_key :id
      varchar   :title, :author
      timestamp :created_at
      text      :description
    end
  end

  def down
    execute 'DROP TABLE books'
  end
end