Okay, now that you have edge Merb and DataMapper installed, let's create our first app. Pick a directory where you want to put your app, and try the following:
$ merb-gen app sample
You should see "Generating with app generator:" followed by a list of the new directories and files Merb added for you. Change into that directory:
cd sample
and edit the config/init.rb file. Uncomment the DataMapper ORM line:
use_orm :datamapper
and also add a dependencies on merb_helpers and merb-assets:
# ==== Dependencies
# These are some examples of how you might specify dependencies.
# Dependency loading is delayed to a later Merb app
# boot stage, but it may be important when
# another part of your configuration relies on libraries specified
# here.
#
dependencies "merb_helpers", "merb-assets"
Finally, if you want to add query logging from DataMapper, add this to the 'after_app_loads' block:
Merb::BootLoader.after_app_loads do
DataObjects::Mysql.logger = DataObjects::Logger.new('log/dm.log', 0)
end
Now, let's set up our databases:
$ rake dm:db:database_yaml
Rename (or move) the generated config/database.yml.sample file to config/database.yml. Then go ahead and enter the correct values for the setup you want. Here's how I have mine:
development: &defaults
# These are the settings for repository :default
adapter: mysql
database: sample_development
username: root
password:
host: localhost
test:
<<: *defaults
database: sample_test
production:
<<: *defaults
database: sample_production
Next, let's create a resource:
merb-gen resource Post title:string body:text created_at:date_time
(NOTE: Run merb-gen with no arguments to see a complete list of generators.)
Make sure that you use 'date_time' and not 'datetime' as you would with ActiveRecord. Otherwise, the created_at field will be assigned the type 'Datetime' (which is wrong), and not the correct 'DateTime'. One other potential gotcha - DataMapper strings will generate a varchar(50) field in MySQL, not varchar(255) like in ActiveRecord.
The merb-gen command will generate a Post model at app/models/post.rb, among other files. Take a look at the file now:
class Post
include DataMapper::Resource
property :title, String
property :body, Text
property :created_at, DateTime
end
You will need to add a property (I put it above the other properties):
because DataMapper requires you to explicitly declare the primary key. Next, go ahead and run the migration:
rake dm:db:automigrate
Note that the dm:db:automigrate task is destructive. If you create any posts, then run the task again, the table will be dropped and recreated, causing you to lose your data.
You will also need to edit config/router.rb, because Merb doesn't add the Post resource to the routes automatically:
Merb::Router.prepare do |r|
# RESTful routes
r.resources :posts
end
Now let's take a look at the views (the posts controller at app/controllers/posts.rb should have everything you need from the merb-gen resource command). I modified my app/views/posts/new.html.erb file to look like this:
<h1>New Post</h1>
<%= error_messages_for :post %>
<% form_for(:post, :action => url(:posts) do %>
<%= partial('form', :button_text => 'Create') %>
<% end %>
<%= link_to 'Back', url(:posts) %>
I moved the form elements into a form partial at app/views/posts/_form.html.erb:
<p>
<label for="post_title">Title: </label><br/>
<%= text_control :title %>
</p>
<p>
<label for="post_body">Body: </label><br/>
<%= text_area_control :body %>
</p>
<p>
<%= submit_button button_text %>
</p>
You can probably guess what the edit view looks like.
Let's fire up merb and take a look in the browser:
(NOTE: enter 'merb --help' to see a complete list of options to the 'merb' command).
Now open up your favorite browser and navigate to 'http://localhost:4000/posts'. You should see something very like this:
Now go ahead and create your first post!
