Ruby on Rails generates model field:type - what are the options for field:type?

:primary_key, :string, :text, :integer, :float, :decimal, :datetime, :timestamp,
:time, :date, :binary, :boolean, :references

See the table definitions section.

To create a model that references another, use the Ruby on Rails model generator:

$ rails g model wheel car:references

That produces app/models/wheel.rb:

class Wheel < ActiveRecord::Base
  belongs_to :car
end

And adds the following migration:

class CreateWheels < ActiveRecord::Migration
  def self.up
    create_table :wheels do |t|
      t.references :car

      t.timestamps
    end
  end

  def self.down
    drop_table :wheels
  end
end

When you run the migration, the following will end up in your db/schema.rb:

$ rake db:migrate

create_table "wheels", :force => true do |t|
  t.integer  "car_id"
  t.datetime "created_at"
  t.datetime "updated_at"
end

As for documentation, a starting point for rails generators is Ruby on Rails: A Guide to The Rails Command Line which points you to API Documentation for more about available field types.

$ rails g model Item name:string description:text product:references

I too found the guides difficult to use. Easy to understand, but hard to find what I am looking for.

Also, I have temp projects that I run the rails generate commands on. Then once I get them working I run it on my real project.

Reference for the above code: http://guides.rubyonrails.org/getting_started.html#associating-models