ActiveRecord 3.0.10 how to overwrite initialize from association?

dubstep · October 1, 2011, 4:38pm

Hello,

I’m trying to implement the EAV pattern in ActiveRecord, for that case
I’ve create two models: Product and ProductType and based on what
ProductType your product is you get dynamically defined accessors.
This way you can use the dynamic attributes by all AR methods, like
#update_attributes, etc. But you can’t directly pass a hash with
dynamic attributes to new.

See the code here:

github.com

edzhelyov/product_manager/blob/master/app/models/product.rb#L5


      
          class Product < ActiveRecord::Base
            belongs_to :product_type
            has_many :product_attributes, :extend => FindersByAttributeName
          
          
  def self.of_type(type)
              ProductType.find_by_name(type).products
            end
          
          
  # This code is run in AR::Base#initialize to populate the product_type_id
            # field just before setting the attributes.
            # Hooking here allow us to have access to the ProductType association, just
            # before the assignment of the attributes' values, so we can define our
            # dynamic setters
            def populate_with_current_scope_attributes
              super

And the corresponding test:

github.com

edzhelyov/product_manager/blob/master/spec/product_spec.rb#L97


      
          
          
  it "defines the attributes only for the product's type" do 
              product.respond_to?(:ram).should be_true
              product.respond_to?(:vendor).should be_false
          
          
    tablet.respond_to?(:ram).should be_false
              tablet.respond_to?(:vendor).should be_true
            end
          
          
end
          
          
context 'with ActiveRecord attributes related methods' do
            it 'works with #update_attributes' do
              product.update_attributes(:price => 10, :ram => 5.0)
          
          
    product.get_dynamic_attribute(:ram).should eq 5
            end
          
          
  it 'works with #new' do
              product = @pt.products.create :price => 10, :ram => 6.0

The test fails with the following:
Failure/Error: product = @pt.products.create :price => 10, :ram
=> 6.0
ActiveRecord::UnknownAttributeError:
unknown attribute: ram
# ./app/models/product.rb:6:in initialize' # ./spec/product_spec.rb:98:in block (3 levels) in <top
(required)>’

This is because the AR#initialize try to call #ram= which is not
defined yet,
if I first try to define the dynamic attributes I don’t have access to
the product_type relation, interesting thing is that I can’t even
access it from the attributes when called with this:
@pt.products.create

Does anyone have any idea how I can make this pass ?

Thanks,
Evgeni