Make ActiveRecord::Base#create respect the :type attribute

I think I've needed and implemented this twice now, so let's make a post about it.

The problem occurs when you are using f.fields_for and nested forms, as per these railscasts, and the nested objects are using STI.

(Will leave a more detailed explanation for future posts).

Update 1: Even though this works as described, I don't think it solves my problem. Will post again if I figure it out...

Update 2: Found this which is I think what I was using last time I had this problem... :S

	#
	# This was causing problems when submitting the nested object form
	# in a/v/product/channels_edit because all the nested channels would
	# be created at plan Channel objects instead of the PrimaryChannel, EusChannel etc.
	#
	# In active record normally :type is ignored, eg:
	# Channel.create(:type='PrimaryChannel', :etc=>1, ...)
	# ignores the type attr and uses 'Channel'.
	#
	# This hack will make it actually use the :type value.
	#
	# Usage:
	#
	# class User < ActiveRecord::Base
	# extend ActiveRecord::CreateWithSubtype
	# ...
	# end
	#
	# class AdminUser < User
	# ...
	# end
	#
	# >> User.create(:type=>'AdminUser', :username=>'simon', ...) #=> #<AdminUser id:123 ...>
	#
	# Actually needed this for nested objects in forms using accepts_nested_attributes_for.
	# http://railscasts.com/episodes/197-nested-model-form-part-2
	#
	# When updating the type is preserved, but when creating a new subobject with the nested form
	# the type is always the base class, which in my case was a problem.
	#
	# (I put this file in lib/active_record/create_with_subtype.rb)
	#
	module ActiveRecord
	module CreateWithSubtype
	def create(attributes=nil, &block)
	# Check if :type attribute exists. Remove it from attributes
	# (Note that attributes can be an array, hence Hash test)
	specified_type = attributes.delete(:type) if attributes.is_a?(Hash)
	if specified_type
	# Find the specified class
	use_sub_class = const_get(specified_type)
	# Sanity check
	raise "'#{use_sub_class}' not a subclass of '#{self}'" unless self.descendants.include?(use_sub_class)
	# Call create on the specified subclass
	use_sub_class.create(attributes, &block)
	else
	# Otherwise, just do the normal thing
	super(attributes, &block)
	end
	end
	end
	end

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