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Cam

2007-Jan-04 09:05 UTC

after_update attributes problem

Hey guys,

I''m having a hard time w/ the  after_update callback on rails... As
far as I can tell, when I define a after_update callback on a model,
the attributes of the object have the same values that they had
*before* Base.save was called.  I''m probably wrong so here''s
the code:

UNIT TEST:
  def test_register_item_adjusts_account_balance
    account = accounts(:cams_credit_card)
    transaction = RegisterItem.new(:date => ''2006-10-31'',
                                   :description => ''Chinese
food'',
                                   :amount => ''-13.44'')
    transaction.account = account
    transaction.save
    assert_equal -113.44, account.balance #this assertion passes

    transaction.amount = -15.50
    transaction.save
    assert_equal -115.50, account.balance  # FAILS

    transaction.destroy
    assert_equal -100.00, account.balance #this assertion will pass
  end

FAILURE OUTPUT:
Loaded suite test/unit/register_item_test
Started
.F.
Finished in 0.202591 seconds.

  1) Failure:
test_register_item_adjusts_account_balance(RegisterItemTest)
[test/unit/register_item_test.rb:31]:
<-115.5> expected but was
<-113.44>.

3 tests, 6 assertions, 1 failures, 0 errors


So changing the amount on a transaction (RegisterItem) should change
the current balance of an account.  Here''s the relevent callbacks:

REGISTER_ITEM UPDATE CALLBACKS:
  def before_update
    account.balance -= amount
    account.save
  end

  def after_update
    account.balance += amount
    account.save
  end

So the idea is that before the transaction is updated i subtract the
amount of the transaction back from the account, and then add the new
amount back on.  It looks like @amount is still the old value during
the after_update callback though.  is that correct? how can i access
the new value?

Thanks,
Cameron Matheson

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Chris Hall

2007-Jan-04 13:00 UTC

head link

Re: after_update attributes problem

the steps are:

before_update
[update operation]
after_update

so to keep things simple, say your account balance is 0.0:

...
# existing transaction
transaction.amount = 10.0 # transaction.account.balance = 0.0 still

transaction.save
  # before_update: transaction.amount = 10.0,
transaction.account.balance = -10.0
  # update operation
  # after_update: transaction.amount = 10.0, transaction.account.balance = 0.0

so you''re back where you started, which is what your test is telling
you.



On 1/4/07, Cam <cameron.matheson-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:>
> Hey guys,
>
> I''m having a hard time w/ the  after_update callback on rails...
As
> far as I can tell, when I define a after_update callback on a model,
> the attributes of the object have the same values that they had
> *before* Base.save was called.  I''m probably wrong so
here''s the code:
>
> UNIT TEST:
>   def test_register_item_adjusts_account_balance
>     account = accounts(:cams_credit_card)
>     transaction = RegisterItem.new(:date =>
''2006-10-31'',
>                                    :description => ''Chinese
food'',
>                                    :amount =>
''-13.44'')
>     transaction.account = account
>     transaction.save
>     assert_equal -113.44, account.balance #this assertion passes
>
>     transaction.amount = -15.50
>     transaction.save
>     assert_equal -115.50, account.balance  # FAILS
>
>     transaction.destroy
>     assert_equal -100.00, account.balance #this assertion will pass
>   end
>
> FAILURE OUTPUT:
> Loaded suite test/unit/register_item_test
> Started
> .F.
> Finished in 0.202591 seconds.
>
>   1) Failure:
> test_register_item_adjusts_account_balance(RegisterItemTest)
> [test/unit/register_item_test.rb:31]:
> <-115.5> expected but was
> <-113.44>.
>
> 3 tests, 6 assertions, 1 failures, 0 errors
>
>
> So changing the amount on a transaction (RegisterItem) should change
> the current balance of an account.  Here''s the relevent callbacks:
>
> REGISTER_ITEM UPDATE CALLBACKS:
>   def before_update
>     account.balance -= amount
>     account.save
>   end
>
>   def after_update
>     account.balance += amount
>     account.save
>   end
>
> So the idea is that before the transaction is updated i subtract the
> amount of the transaction back from the account, and then add the new
> amount back on.  It looks like @amount is still the old value during
> the after_update callback though.  is that correct? how can i access
> the new value?
>
> Thanks,
> Cameron Matheson
>
> >
>
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Steve Koppelman

2007-Jan-04 14:58 UTC

head link

Re: after_update attributes problem

Would calling account.reload after the save cause problems for you
elsewhere?

Cameron Matheson wrote:> Hey guys,
> 
> I''m having a hard time w/ the  after_update callback on rails...
As
> far as I can tell, when I define a after_update callback on a model,
> the attributes of the object have the same values that they had
> *before* Base.save was called.  I''m probably wrong so
here''s the code:
.... <snip>> Here''s the relevent callbacks:
> 
> REGISTER_ITEM UPDATE CALLBACKS:
>   def before_update
>     account.balance -= amount
>     account.save
>   end
> 
>   def after_update
>     account.balance += amount
>     account.save
>   end
-- 
Posted via http://www.ruby-forum.com/.

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Cam

2007-Jan-04 19:57 UTC

head link

Re: after_update attributes problem

Hey thanks for the response:

On 1/4/07, Chris Hall
<christopher.k.hall-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:> so to keep things simple, say your account balance is 0.0:
> ...
> # existing transaction
> transaction.amount = 10.0 # transaction.account.balance = 0.0 still
>
> transaction.save
>   # before_update: transaction.amount = 10.0,
> transaction.account.balance = -10.0
>   # update operation
>   # after_update: transaction.amount = 10.0, transaction.account.balance =
0.0
>
> so you''re back where you started, which is what your test is
telling you.
Ok so there is a problem in the way i understand the before_update
callback, or in your logic (probably my problem which would explain
the bug).  Anyway, this is a before/after_*update* callback, it looks
like the scenario you''re describing is a before/after_*create* kind of
deal.  so the way i would understand it would be like so:

#account.balance == 0
transaction.amount = 10.0 #transaction.amount formerly == 0
before_update: transaction.amount -= 0\
after_update: transaction.amount += 10
# account.balance == 10

is that wrong?
Cameron Matheson

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Cam

2007-Jan-04 19:58 UTC

head link

Re: after_update attributes problem

Hey Steve,

On 1/4/07, Steve Koppelman
<rails-mailing-list-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org>
wrote:>
> Would calling account.reload after the save cause problems for you
> elsewhere?
>
I wasn''t aware of the reload method.  I called it after save and
although it didn''t cause any problems, it didn''t change the
behavior
of the program either (unless i called self.reload on the transaction,
in which case it looks like the after_update callback didn''t get
called)

Thanks!
Cam

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Chris Hall

2007-Jan-16 12:50 UTC

head link

Re: after_update attributes problem

these are the callbacks that are run during an update operation

before_validation
before_validation_on_update
after_validation
after_validation_on_update
before_save
before_update
<UPDATE OPERATION>
after_update
after_save

if you are creating a new record, replace *_update with *_create in
the above list.  thats the difference.

so, knowing this, we see that your before and after updates will run
around the update operation.

# transaction.account.balance = -100.00
transaction.amount = -15.50
   transaction.save # before_update, update, after_update

   # before_update callback
   # -----------------------------------
   # account.balance -= amount
   # -100.00 - (-15.50) = -(100.00 - 15.50) = -84.50
   # account.save
   #
   # transaction update operation
   #
   # after_update callback
   # --------------------------------
   # account.balance += amount
   # -84.50 + (-15.50) = -(84.50 + 15.50) = -100.00
   # account.save
   #

   assert_equal -115.50, account.balance  # FAILS


<start before_update>
account.balance -= amount # 113.44, as 100.00 - (-13.44) = 100.00 +
13.44 = 113.44
account.save # balance of 113.44 is saved to db
<end before_update>

<transaction update operation>

<start after_update>
account.balance += amount # 100.00, as 113.44 + (-13.44) = 113.44 -
13.44 = 100.00
account.save # balance of 100.00 is saved to the db
<end after_update>

and so you are right back where you started as far as your
account.balance goes, which is exactly what your test is telling you.

follow?

Chris

On 1/4/07, Cam <cameron.matheson-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:>
> Hey thanks for the response:
>
> On 1/4/07, Chris Hall
<christopher.k.hall-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> > so to keep things simple, say your account balance is 0.0:
>
> > ...
> > # existing transaction
> > transaction.amount = 10.0 # transaction.account.balance = 0.0 still
> >
> > transaction.save
> >   # before_update: transaction.amount = 10.0,
> > transaction.account.balance = -10.0
> >   # update operation
> >   # after_update: transaction.amount = 10.0,
transaction.account.balance = 0.0
> >
> > so you''re back where you started, which is what your test is
telling you.
>
> Ok so there is a problem in the way i understand the before_update
> callback, or in your logic (probably my problem which would explain
> the bug).  Anyway, this is a before/after_*update* callback, it looks
> like the scenario you''re describing is a before/after_*create*
kind of
> deal.  so the way i would understand it would be like so:
>
> #account.balance == 0
> transaction.amount = 10.0 #transaction.amount formerly == 0
> before_update: transaction.amount -= 0\
> after_update: transaction.amount += 10
> # account.balance == 10
>
> is that wrong?
> Cameron Matheson
>
> >
>
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Cameron Matheson

2007-Jan-21 22:24 UTC

head link

Re: after_update attributes problem

hey,


On 1/16/07, Chris Hall
<christopher.k.hall-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:> follow?
it makes sense... i hadn''t understood how it worked previously.  i
figured that since it was before save was called, that the data would
have been the old data.  so is there no way to access the previous
data w/ callbacks?  i guess i could store the old amount in all of the
RegisterItem model, but i''d rather not go that route.

thanks,
cam

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