Passing additional parameters to Rails Generate Model?

I'm new to Ruby and Rails and I'm running Rails 3 on Ruby 1.9.2.

I want to create a model, so I looked at the documentation to get the table definition that I want, but I wonder how I would pass this to rails generate model?

Basically I want this:

title :string, :null => false
details :text, :limit => 30000, :null => false

But I can only specify the column name and type, not :null or :limit.

I've tried rails model generate Article (title:string, :null => false) (details:text, :limit=>30000, :null => false) but that just tells me that ( is an unexpected token.

If I just generate the model with title:string details:text then the article.rb file is empty, presumably because it's read from the DB anyway.

As everything in Rails is supposed to be a) simple and b) magic, I'm wondering if I'm just missing something and have to pass something like a hash to generate model? Or do I really have to manually edit the migration .rb file?