Guide to Getting Started with Merb and ActiveRecord

3 April, 2008

Spent a while today getting up and running with Merb, the minimalist modular alternative Ruby framework from Ezra and the good people at Engine Yard. Merb has been in a bit of chaos these recent months as it's gone through a major reworking to acheive a whole new level of performance as well as honest-to-goodness modularity, including choosing your own ORM and templating system. I've been watching Merb's development for some time waiting for it to get to a level of stability that looked safe enough to dive in; their most recent release, 0.9.2, combined with pressing needs in a few exciting new Grabb.it features, made today the day.

My first day with Merb has been mostly great, but the one thing I found really sorely missing was a tutorial on how to get started. In all fairness, the Merb team promises left and right that copious documentation will be coming as they settle down to 1.0. In the meantime, I thought I'd pitch in for any brave early adopters out there with this Guide to Installing Merb and ActiveRecord.

Acquire and Install the Source

So, my goal here was to get from 0 (no Merb on my machine whatsoever), to running a hello world for accessing the database from an existing Rails project using ActiveRecord from within Merb. The first step was to acquire the source. One of the downsides to Merb's modular architecture is the complexity involved with installing it (again, all relevant disclaimers here about how the merb team will, I'm sure, be working to simplify and improve the process as they reach 1.0). At least for now, you actually have to get your hands on three different packages: merb-core (the base of the framework, a requirement), merb-more (has more advanced features like the command for actually creating a new app), and merb-plugins (this is where things like ORMs and templating systems live). Let's do that:

$ git clone git://github.com/wycats/merb-core.git
$ git clone git://github.com/wycats/merb-more.git
$ git clone git://github.com/wycats/merb-plugins.git

That'll get us the bleeding edge trunk version (about which more here).

Now that we've got the pieces, we need to install them, thusly:

$ cd merb-core ; rake install ; cd ..
$ cd merb-more ; rake install ; cd ..
$ cd merb-plugins/merb_activerecord; rake install; cd ..

Create a New Project and Configure it for Active Record

We've got all the pieces; it's time to create our project and get it setup to use ActiveRecord. Go to the place you want to create your app and do this:

$ merb-gen app my_app

This is equivalent to the 'rails' command and will create your project directoy with most of what you need. But since a basic project in Merb is assumed to be simpler than a basic project in Rails, you'll quickly notice that you don't have a models directory. Since we're actually going to need a model if we want to connect up to a database with ActiveRecord, go ahead and create that directory and create a file inside if for your model just as you would in Rails, for example my_resourece.rb, which could look like this:

class MyResource < ActiveRecord::Base
end

We'll probably want a controller as well, so create a new file: controllers/my_resources.rb:

class MyResources < Application
def show
r = MyResource.find :first
render r.some_method
end
end

Notice that all Merb controllers inherit from Application just like Rails controllers inherit from Application::Controller. The naming choice there is kind of interesting because it reveals Merb's controller-centric history and philosophy (remember that the framework doesn't assume that we need models by default; it turns out there's a lot you can do with just controllers).

Since we're using ActiveRecord, we'll obviously need to tell Merb that we want it to go ahead and actually load AR as our ORM. Go into config/init.rb in your project and uncomment the line that says "use_orm :activerecord".

We're almost there! These last few steps will feel familiar from setting up a Rails app: letting the framework know about our route and database configuration. To set up your route, open up config/router.rb and, inside the 'prepare' block, add a line like this:

r.resources :my_resources

Merb's routes work pretty much like Rails's, but with a few more advanced features some of which are explained in the comments at the top of that file. If you need something other than standard RESTful routing, read those.

Finally, all we've got to do is configure database access and we'll be ready to roll. In Merb this looks exactly like Rails, in fact, I simply copied the database.yml file over from the Rails project that usually manages the db I wanted to access, dropped it in config/databse.yml and it worked straight out of the box.

Ok! If you've made it this far, then you're probably more than ready for the big reveal. In you project directory do this:

$ merb

The server will start and you'll get a few log messages in your terminal that look like this:

$ merb
~ Loaded DEVELOPMENT Environment...
~ loading gem 'merb_activerecord' from ...
~ loading gem 'activerecord' from ...
~ Connecting to database...
~ Compiling routes...
~ Using 'share-nothing' cookie sessions (4kb limit per client)
~ Using Mongrel adapter

Once that settles down, browse to http://localhost:4000 and you should see the Merb welcome screen. Go to your expected url to see the result of your handiwork: i.e. http://localhost:4000/my_resources/7

If this works, you're officially up and running with Merb and ActiveRecord. If not, you'll see one of Merb's very stylish error screens and it'll be time to go to #merb on irc.freenode.net where all the friendly merbfolk hang out and are more than willing to help.

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