Updating attribute on dependent of many-to-on association

All,

I posted this over on comp.lang.ruby, but realized I should probably
keep Rails questions to this group, so soory for the cross-post.

I have a rails app with a Transaction class that has_many :entries.
Each Transaction has many entries, and those with the debit attribute
true are debits, false are credits. It starts like this.

class Transaction < ActiveRecord::Base
  has_many :entries
  has_many :debits, :class_name => 'Entry', :conditions => {:debit =>
true}
  has_many :credits, :class_name => 'Entry', :conditions => {:debit =>
false}
end

I want to be able to complete an Transaction if there is exactly one
Entry that has its amount set to nil. I want to set that amount to a
debit or credit of the proper amount to make the Transaction balance.

Sounded easy to me, but I am having trouble with my balance! method.
The relevant part of it is:

  def balance!
    ...
    if num_nils == 1
      # Set the sole nil entry to amount needed to balance Transaction
      plug = debit_total - credit_total
      entries.where(:amount => nil).each do |e|
        e.amount = plug.abs
        e.debit = (plug < 0)
        e.save
      end
    end

The problem is that when I finish this, the entries associated with my
Transaction are not affected. I appears to make a copy, change it,
and
leave the Entry associated with my Transaction with a nil amount.

What am I missing?

Thanks,

Dan Doherty

All,

I posted this over on comp.lang.ruby, but realized I should probably
keep Rails questions to this group, so soory for the cross-post.

I have a rails app with a Transaction class that has_many :entries.
Each Transaction has many entries, and those with the debit attribute
true are debits, false are credits. It starts like this.

class Transaction < ActiveRecord::Base
has_many :entries
has_many :debits, :class_name => 'Entry', :conditions => {:debit =>
true}
has_many :credits, :class_name => 'Entry', :conditions => {:debit =>
false}
end

I want to be able to complete an Transaction if there is exactly one
Entry that has its amount set to nil. I want to set that amount to a
debit or credit of the proper amount to make the Transaction balance.

Sounded easy to me, but I am having trouble with my balance! method.
The relevant part of it is:

def balance!
...
if num_nils == 1
# Set the sole nil entry to amount needed to balance Transaction
plug = debit_total - credit_total
entries.where(:amount => nil).each do |e|
e.amount = plug.abs
e.debit = (plug < 0)
e.save
end
end

The problem is that when I finish this, the entries associated with my
Transaction are not affected. I appears to make a copy, change it,
and
leave the Entry associated with my Transaction with a nil amount.

What am I missing?

The first thing to determine is which bit is failing. Is the code in
the each loop actually running? Does the save work (check the return
code from save)? Have a look at the Rails Guide on debugging for help
on how to debug the code.

Not directly related to the question but I find it hard to believe
that the way you are going about this is ideal. I suggest it would be
better not do directly differentiate between debits and credits as you
are, but just to have positive or negative transaction values.
However as I know little about what you are trying to achieve this may
be incorrect.

Also I suspect that transaction may be a reserved word in rails, so
this might give you problems.

Colin

Colin,

Thanks for taking a look at this. After a good night’s sleep, I came back to this, and the problem appears to be
that I need to self.reload after the loop. I believe this is because of the nature of the association, which depend on whether
debit is true or false, and I believe need re-reading from the db after the e.save.

For anyone interested, here is what fixed it:

if num_nils == 1

  # Set the sole nil entry to amount needed to balance Transaction

  plug = debit_total - credit_total

  entries.where(:amount => nil).each do |e|

    e.amount = plug.abs

    e.debit = (plug < 0)

    e.save

  end
  reload    # <= New line
end

Th