Rails - Oct 2005 - initialising an instance variable on ActiveRecord creation

Hallo, I have a table like this:

create table properties(
id bigint unsigned not null auto_increment,
property_variable_stack_id bigint unsigned not null,
primary key(id),
foreign key (property_variable_stack_id) references
property_variable_stacks (id))
type=InnoDB;

Here you can see a reference to a table
property_variable_stacks.
>From outside the Property class I can set up a Property with a
PropertyVariableStack like this:
p=Property.new
p.property_variable_stack=PropertyVariableStack.new
p.save!

This works just fine.
However, I have not been able to create a new PropertyVariableStack
automatically for each new Property -- I have tried before_create,
after_create, initialize... All to no avail.
For example, the code I tried for initialize in Property was:

def initialize
  @property_variable_stack=PropertyVariableStack.new
end

When this ran, I could trace all the correct SQL being generated in
the logs, but it raised an error:
test_sample(TestPropertyLoader) [Z:/sics/test/tc_property_loader.rb:66]:
Exception raised:
Class: <NoMethodError>
Message: <"undefined method `construct_sql'' for
#<PropertyVariableStack:0x2c77d0
8>">

Can anyone tell me why this is?
& maybe advise on how to achieve what I''m after?

Thanks in advance,

   doug.

doug livesey wrote:
> However, I have not been able to create a new PropertyVariableStack
> automatically for each new Property -- I have tried before_create,
> after_create, initialize... All to no avail.
> For example, the code I tried for initialize in Property was:
> 
> def initialize
>   @property_variable_stack=PropertyVariableStack.new
> end
def initialize
  super
  self.property_variable_stack = PropertyVariableStack.new
end

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