ActiveRecord: update a foreign key in an association table

Rails
1

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

2

On 20 March 2011 15:30, Fabrice F. [email protected] wrote:

has_many :accounts, :through => :splits
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

3

On Mar 20, 3:30pm, Fabrice F. [email protected] 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

4

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