Hmm, it's behaviour seems weird although I might be missing something as well.

I tried your example and editing a tasks attributes seems to work, adding a new one does not:

ruby-1.9.2-p0 > p = Project.create!(:name => 'project')
 => #<Project id: 3, name: "project", created_at: "2010-09-08 10:35:31", updated_at: "2010-09-08 10:35:31"> 
ruby-1.9.2-p0 > p.tasks.create!(:name => 'task 1')
 => #<Task id: 4, name: "task 1", project_id: 3, created_at: "2010-09-08 10:35:39", updated_at: "2010-09-08 10:35:39"> 
ruby-1.9.2-p0 > p.tasks_attributes = [ { :id => 4, :name => 'changed'} ]
 => [{:id=>4, :name=>"changed"}] 
ruby-1.9.2-p0 > p.save
 => true 
ruby-1.9.2-p0 > p.tasks
 => [#<Task id: 4, name: "changed", project_id: 3, created_at: "2010-09-08 10:35:39", updated_at: "2010-09-08 10:36:06">] 
ruby-1.9.2-p0 > p.tasks_attributes = [ { :name => 'new task' } ]
 => [{:id=>5, :name=>"new task"}] 
ruby-1.9.2-p0 > p.save
 => true 
ruby-1.9.2-p0 > p.tasks
 => [#<Task id: 4, name: "changed", project_id: 3, created_at: "2010-09-08 10:35:39", updated_at: "2010-09-08 10:36:06">] 
ruby-1.9.2-p0 >

Can someone verify my patch and provide comments. Thanks.

Hi Neeraj,

Your patch works well for me. I ran the tests and they pass.

I also ran your patch against the OP code and the patch rejects the name change on the task, just as it is supposed to.

Thanks

+1

@Lake thanks for verifying.

Hi there. Though I'm using rails-3.0.3 (and of course activerecord-3.0.3) I'm facing this very same issue, exactly same behaviour. FTR, here's my sources:

app/models/invoice.rb

class Invoice < ActiveRecord::Base

attr_accessible :tax, :discount, :modifier, :paid, :issue_date, :payment_date, :description, :items_attributes
has_many :items, :class_name => 'InvoiceItem', :dependent => :destroy
accepts_nested_attributes_for :items, :reject_if => proc { |a| a[:description].blank? }, :allow_destroy => true

end

app/models/invoice_item.rb

class InvoiceItem < ActiveRecord::Base

attr_accessible :price, :discount, :description
belongs_to :invoice

end

I could verify that the :reject_if is honoured when creating a new Invoice, while it's not when updating an existing one.

The proc (or symbol to a method) given to an accept_nested_attributes_for method for a has_one association never runs (for me, on Rails 3.0.3). Did anyone give that one a test?

@Dave - could you write a failing test case ?