Rails - Mar 2005 - Unit Tests - Is this right?

On 11.3.2005, at 10:03, Adelle Hartley wrote:
>
>     # account is dependent, therefore is destroyed when reference to 
> owner
> is lost
This comment indicates that the relationship is specified as dependent. 
In that case I would certainly expect the orphaned row to be deleted, 
too, i.e.  (ii). Otherwise there wouldn''t be any use for
"dependent =>
true". Of course the code needs to be prepared for situations where the 
user has used referential integrity constraints in his db, so that it 
won''t bomb even if the dependent row was deleted already by the db.
> (ii)  ActiveRecord should delete the unused record from the Accounts 
> table
> and Account.find(old_account_id) should raise an exception (which is 
> what
> the test currently expects but doesn''t get).
>
> Personally, I prefer to let the RDBMS take care of these kinds of 
> issues
> (ie, I prefer the first option).  Even if I didn''t prefer it that
way,
> a
> legacy database might have referential integrity rules setup such that
> ActiveRecord would be duplicating effort in this instance.
Yes, but there are databases (may I name MySQL) that don''t support 
referential integrity, so taking away that functionality from Rails 
would be a big disadvantage for users of them. You can always leave the 
dependency declaration away from your model definition if you just want 
to depend on your database in these issues.

Cheers,
//jarkko

--
Jarkko Laine
http://jlaine.net
http://odesign.fi


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Hi all,

I''ve been working on cleaning up the unit tests for ActiveRecord. 
Here''s
one of the errors/failures that I get when I run the tests for MySql:

  1) Failure:
test_natural_assignment_to_nil(HasOneAssociationsTest)
[./test/associations_test.rb:98]:
<ActiveRecord::RecordNotFound> exception expected but none was thrown.

The source for this test is a follows:

  def test_natural_assignment_to_nil
    old_account_id = @signals37.account.id
    @signals37.account = nil
    @signals37.save
    assert_nil @signals37.account
    # account is dependent, therefore is destroyed when reference to owner
is lost
    assert_raises(ActiveRecord::RecordNotFound) {
Account.find(old_account_id) } 
  end

What exactly is the desired behaviour here?  I would expect that either:

(i)  We end up with an orphaned record in the Accounts table and
Account.find(old_account_id) shouldn''t raise an exception (which is
what is
currently happening)

OR

(ii)  ActiveRecord should delete the unused record from the Accounts table
and Account.find(old_account_id) should raise an exception (which is what
the test currently expects but doesn''t get).

Personally, I prefer to let the RDBMS take care of these kinds of issues
(ie, I prefer the first option).  Even if I didn''t prefer it that way,
a
legacy database might have referential integrity rules setup such that
ActiveRecord would be duplicating effort in this instance.

What do other people here think?  I haven''t been using ActiveRecord
long
enough to know whether this area had already been addressed.

Adelle.

Jarkko Laine wrote:
> Yes, but there are databases (may I name MySQL) that don''t 
> support referential integrity, so taking away that 
> functionality from Rails would be a big disadvantage for 
> users of them. You can always leave the dependency 
> declaration away from your model definition if you just want 
> to depend on your database in these issues.
Thanks.  I hadn''t spotted the "dependent => true".

I am pretty close to crying "uncle" on the subject of how this is
supposed
to be implemented.
>From ActiveRecord/base.rb:
        def association_accessor_methods(association_name,
association_class_name, association_class_primary_key_name, options,
association_proxy_class)
		.....
		.....
          define_method("#{association_name}=") do |new_value|
            association =
instance_variable_get("@#{association_name}")
            if association.nil?
              association = association_proxy_class.new(self,
                association_name, association_class_name,
                association_class_primary_key_name, options)
            end
            association.replace(new_value)
            unless new_value.nil?
              instance_variable_set("@#{association_name}",
association)
            else
# this is where "test_natural_assignment_to_nil" ultimately sends us.
              instance_variable_set("@#{association_name}", nil)
              return nil
            end
            association
          end
        end


I''ve commented the line where we ultimately end up during
"test_natural_assignment_to_nil".

I''m still getting the hang of the "Ruby/ActiveRecord Way", so
is this where
the record should be deleted, or is there a more appropriate mechanism (such
as modifying the definition of "instance_variable_set")?

Adelle.