Rails - Mar 2011 - ActiveRecord: update a foreign key in an association table

Hello,

I''d like to know how to update a foreign key in an association table
(many_to_many association) ?

Here is my model, Split is the association table between Account and
Transaction:

class Account < ActiveRecord::Base
    set_primary_key :guid

    has_many :splits, :foreign_key => ''account_guid'',
:primary_key =>
''guid''
    has_many :transactions, :through => :splits
end

class Transaction < ActiveRecord::Base
    set_primary_key :guid

    has_many :splits, :foreign_key => ''tx_guid'',
:primary_key =>
''guid''
    has_many :accounts, :through => :splits
end

class Split < ActiveRecord::Base
    belongs_to :transaction, :foreign_key => ''tx_guid'',
:primary_key
=> ''guid''
    # here is the association that I''d like to change:
    belongs_to :account, :foreign_key => ''account_guid'',
:primary_key
=> ''guid''
end

I''m trying this but it does not work (the value is not updated):

account = Account.new
transaction.splits.first.account = account
# error: prints the old value of account
puts transaction.splits.first.account

Do you have any idea ? Do I need to create a new Split and delete the
old one or is it possible to update the existing one ?

Thank you for your help,

Fabrice

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On 20 March 2011 15:30, Fabrice Fabrisss
<lists-fsXkhYbjdPsEEoCn2XhGlw@public.gmane.org>
wrote:
> Hello,
>
> I''d like to know how to update a foreign key in an association
table
> (many_to_many association) ?
>
> Here is my model, Split is the association table between Account and
> Transaction:
>
> class Account < ActiveRecord::Base
>    set_primary_key :guid
>
>    has_many :splits, :foreign_key => ''account_guid'',
:primary_key =>
> ''guid''
>    has_many :transactions, :through => :splits
> end
>
> class Transaction < ActiveRecord::Base
>    set_primary_key :guid
>
>    has_many :splits, :foreign_key => ''tx_guid'',
:primary_key =>
> ''guid''
>    has_many :accounts, :through => :splits
> end
>
> class Split < ActiveRecord::Base
>    belongs_to :transaction, :foreign_key => ''tx_guid'',
:primary_key
> => ''guid''
>    # here is the association that I''d like to change:
>    belongs_to :account, :foreign_key =>
''account_guid'', :primary_key
> => ''guid''
> end
>
> I''m trying this but it does not work (the value is not updated):
>
> account = Account.new
> transaction.splits.first.account = account
> # error: prints the old value of account
> puts transaction.splits.first.account
Did you save the split after updating it?
transaction.splits.first.account will go back to the database.  Try
something like
split = transaction.splits.first
split.account = account
split.save!

You might need to reload transaction to get it to notice the change.

Is this GnuCash by any chance?  I have written a read-only rails
interface for GnuCash for report generation.

Colin

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On Mar 20, 3:30 pm, Fabrice Fabrisss
<li...-fsXkhYbjdPsEEoCn2XhGlw@public.gmane.org> wrote:
> I''m trying this but it does not work (the value is not updated):
>
> account = Account.new
> transaction.splits.first.account = account
> # error: prints the old value of account
> puts transaction.splits.first.account
>
> Do you have any idea ? Do I need to create a new Split and delete the
> old one or is it possible to update the existing one ?

If the collection (in this case transaction.splits) isn''t loaded then
foo.first (and foo.last) will fetch just that one row from the
database.
The way it''s implemented, foo.first returns a fresh object each time,
so  transaction.splits.first.account = account does assign account to
that split, however

when you call  transaction.splits.first.account it''s fetching a fresh
copy of that split.

if you did foo = transaction.splits.first; foo.account = account then
you''d be able to see that the assignment did actually happen


Fred
>
> Thank you for your help,
>
> Fabrice
>
> --
> Posted viahttp://www.ruby-forum.com/.
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Thank you for your advice,
> Colin, yes, it''s a GnuCash application which assigns an account to
transactions
based on keywords

I solved my problem by defining a primary key on the association table 
''Splits'':

class Split < ActiveRecord::Base
  set_primary_key :guid
  ...
end

Sincerely,

Fabrice

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