Why I am a DataMapper convert (it makes BDD happy)

T here’s lots of buzz around DataMapper right now, especially among the #merb crowd. I haven’t had any major issues with ActiveRecord, so I haven’t needed to look at a new ORM…but I like to play with new things, so last night I really gave the DM a try.

I’m a complete convert, if for no other reason that the awesome way automigrations play along with BDD.

First, tell your spec_helper to use automigrations:

DataMapper::Base.auto_migrate!

This will cause your database tables to be dropped and re-created so use with caution.

Next, let’s spec some behavior:

it "should have a username field" do
  @person.username = "jjames"
  @person.username.should == "jjames"
end

And see what autotest says:

....F.....

1)
NoMethodError in 'Person should have a username field'
undefined method `username=' for #<person:0x13f720c>
./spec/models/person_spec.rb:38:

Finished in 0.049775 seconds

10 examples, 1 failure

Cool, that’s what we expected. Now, with ActiveRecord, to get to green, we’d need to create a migration and run it. With DataMapper, we stay in our model:

class Person < DataMapper::Base
  property :username, :string
end

And autotest says…

..........

Finished in 0.040584 seconds

10 examples, 0 failures

Now, is this perfect? Not yet. DM has a good amount of work still. There’s some smart folks working on it, and I bet it will be pretty sweet in a few more weeks.

But, man…that’s just awesome.