Validate number of nested attributes

Question

I have a model with nested attributes :

class Foo < ActiveRecord::Base
    has_many :bar
    accepts_nested_attributes_for  :bar
end

It

Answer 1

Just in case anyone seeing this needs it to work for Rails 3. I think the add_to_base (that Tony and Jeremy use) has been removed so it needs to be like so:

class Foo < ActiveRecord::Base
  has_many :bars
  accepts_nested_attributes_for  :bar

  def validate
    if self.bars.reject(&:marked_for_destruction?).length < 2
      self.errors.add(:base, "Must have at least 2 bars")
    end
  end
end