Merb-tastic

posted by hampton on December 3rd, 2007

Here at the Unspace offices we've been nerding around with Merb a lot recently. If you don't know what Merb is, its a super-light framework written by Ezra Zygmuntowicz from Engine Yard. If you want to be more specific, its really a re-write of Rails' ActionPack that integrates directly into Mongrel with small bits of glue around to make it a framework (folders, folders everywhere!).

Merb is highly influenced by Rails. That might be an understatement. Anyone who knows Rails will quickly find Merb to be very familiar, but with a few key differences. Mostly, Merb is built around the philosophy of keeping it as light as possible. Don't come looking for AJAX helpers, ORMs built-in, large core extensions, or lots of the other cushy niceties that Rails provides by default. Most of these things can be installed into Merb quickly using gems, but they aren't in the basic Merb install.

This makes for a different feeling experience. Merb requires a little more legwork from you as the developer, but it also steps out of your way more often than Rails does. Merb is like Rails for those who want to hack around with more freedom.

I probably wouldn't recommend someone new to Ruby to start with Merb. Start with Rails for many, many reasons. Most of all, Rails skills are far more bankable than claiming Merb skills (for the time being at least). Most people don't know what Merb is. Also, Rails teaches you lots of good things. Its when you start to feel the edges of Rails that you want to push out of them and customize your framework more that Merb starts to become a good option.

Also, Merb is fantastically fast. The original idea behind Merb was to do Mongrel and ERB (M+Erb) together and make them work as quickly as possible. The inspiration was Rails for the way the original version was built. However, as time has gone on, the code has expanded into being a real development powerhouse for experienced Ruby developers. Did I mention that its fast as shit...? I don't find Rails prohibitively slow, but when you start to see how quickly Merb uses Ruby to produce HTTP requests my nipples start to get hard. I've seen 500 requests a second for a basic request on my commodity box. Checkout the benchmarks against Rails.

ORMs

Merb is ORM-agnostic which means that you can choose whatever ORM you want. Its easy to write ActiveRecord models just as easily as Rails, or you can experiment with some of the up-and-coming Ruby ORMs like DataMapper and Sequel.

DataMapper

DataMapper is the closest to ActiveRecord, but it has a lot more magic when it comes to handling attributes associated with your models. Imagine if you didn't have to write migrations for your models because they were smart enough to know how to express themselves in the database.

Let's look at this example.

class Zoo < DataMapper::Base
  property :name, :string, :default => 'Unknown'
  property :notes, :text
  property :updated_at, :datetime

  has_many :exhibits

  validates_presence_of :name
end

In this example, DataMapper sees that you want a property called :name when it is loaded and so it checks to make sure that the column is there. If it isn't it builds it for you. Did I mention that DataMapper is thread-safe? That means that Merb can run in all of its multi-threaded glory. I'll be honest that I haven't gotten to use this one much, but I know the developers are working hard to expand its feature base and have it in extremely active development. Read more about it here.

Sequel

Sequel is a type of ORM that I've never really come across before. It is focused much more on building queries than DM or AR are. You basically construct these objects using Ruby syntax that represent an un-executed query object. Let's build one here that will get us all of the users who are admins and in the order that they were created.

DB = Sequel.open 'mysql://root:1234@localhost/test_database'
admin_list = DB[:users].filter(:is_admin => true).order(:last_name)

Now, this is just a symbolic object at this point. Nothing has been executed. We can execute the command using Enumerable-style interfacing

admin_list.collect do |user|
  "#{user[:last_name]}, #{user[:first_name]}"
end
#=> ["Bergin, Candace", "Ferrier, Emerson"]

Every time we execute collect on that object, we get a fresh new query with new data. So, Sequel isn't a replacement for DM or AR, but it does give us a really awesome and speedy way to interact with our database. I am looking to use this in some places where I need some super-fast and simple queries to be run in a lightweight section of one of my applications.

Views

Well, I would be remiss not to mention that Merb is one of the new crop of frameworks that supports Haml out-of-the-box. Not only that, but it defaults to Erubis and has built-in support for Markaby. If you have the gem installed for any of these, Merb magically begins to work with them. My only note about integrating Haml with it is that right now you have to add a line to your config/dependencies.rb file to get Sass stylesheets to render properly in your Merb application.

dependency 'haml'

That should do it. You now have the full Haml/Sass suite running in your Merb application. Easy as your momma.

Et Cetera

Some of the other differences between Rails that I really like are....

• Mailers have their own directory in /app/mailers
• config/dependencies.rb is a nice place to declare all of your gem requirements instead of a messy plugin folder.
• If you "freeze edge" the framework puts itself into a folder called "framework"
• As long as you don't use ActiveRecord, you can use multi-threading.
• DRb is built in and easy as pie.

Installation

Its as simple as....

$ sudo gem install merb -y

but of course you'll also want to...

$ sudo gem install merb_datamapper datamapper haml erubis -y

Yup, that's it. Now generate a project this way

$ merb -g project_name

Are you sure you're getting this? I know its complicated. If you're scared just go back to PHP and hug your doll. Now, go dive into that and see what you can figure out with your Rails-fu. You'll be surprised at how familiar it feels.

Final Thoughts

Merb isn't some perfect "Rails killer". However, its a really interesting framework that will hopefully make Rails answer to some of its long-standing claims (performance isn't that important) and keep the Rails core team on their toes. Flat out, competition is good. Extra frameworks in Ruby doesn't mean that we dilute some special chemical in the community, but it means that we can start to focus on solving the problems for our applications and not making our applications fit our solution.

This is especially true if you are starting an application that you know needs to be high-performance. Merb is the place to go for that then. That's the case at Unspace right now. We are working on a project that requires unbelievably high uptime and request performance in order to be tenable. Rails just simply isn't the solution for that. Its why 37s wrote a C library to build Campfire with... because Rails is just not built for that kind of thing. Does that make Rails bad? No way! Rails is fantastic and will continue to be fantastic into the future. However, now there is a new kid on the block that is worth consideration for new projects where Rails isn't a perfect-fit.

Stay tuned for more from Unspace with Merb though. We've even already started patching Merb and we'll soon be announcing our new internal project that uses Merb to handle possibly millions of requests quickly. First we have to get the patent filed.