Polymorphic Camping

For one of the projects I’m doing at Cardinal, I’m using a polymorphic association. The nature of Camping is to write terse, yet simple code. For example, creating a new record in a controller is normally done in a one-liner, like so:

class Add
  def post
    @person = Person.create(:name => input.person_name, :age => input.person_age)
    redirect R(List)
  end
end

Here’s something that I got caught up on for 20 minutes this morning. When adding polymorphic associations, make sure that the [polymorphic name]_type field includes all the namespace information. Here’s an example:

def Person < Base 
    has_many :addresses, :as => :addressable 
end

def Address < Base 
    belongs_to :addressable, :polymorphic => true 
end

...
label 'Type', :for => 'addressable_type'; br
addressable_select("addressable_type"); br
label 'person', :for => 'person_id'; br
person_select("person_id", @people); br
...

# controller
class Add
  def post
    @addressable = Person.find(input.person_id) if input.addressable_type == "Person"
    @address = Address.create(:street => input.address_street, 
                                          :city => input.address_city,
                                          :state => input.address_state, 
                                          :zip => input.address_zip,
                                          :addressable_type => @addressable.class,  #use the class name to get namespace
                                          :addressable_id => @addressable.id)
    redirect List
  end
end

There’s a number of ways to solve this, although I found this to be the simplest for a form where you can select multiple models. The point is to make sure that you have that namespace information in the database, otherwise you will receive “Uninitialized Constant” errors for the addressable class.

Happy Camping!