accepts_nested_attributes_for & :reject_if. How to prevent rejection until parent association saves?

Question

class Gift < ActiveRecord::Base
  has_many :contributions
  accepts_nested_attributes_for :contributions, :reject_if => proc { |a| a['amount'].blank? }

Contribution has a :nickname attribute. In the :new form, it is pre-populated with the user's real name. A user might decide to change it to "Uncle Bob" (or whatever). Unfortunately, with :reject_if, if no amount is specified in the contribution, the :nickname change is lost when :new reloads in cases where @gift is not valid. This happens because the nested contribution_attributes are rejected. How do we preserve the :nickname change and only handle the rejection when @gift is actually saved?

Answer 1

I think you're looking for a validation in the Contribution model instead of a :reject_if clause.

:reject_if will throw away the entire record if the condition is met. Failed validations in the contribution model will block the associated gift from being saved. However @gift will retain the contribution regardless of its amount value on a failed save, allowing your user the chance to correct it, when the controller renders the new action again.

The solution is to remove the :reject_if clause from the accepts_nested_attributes_for statement, and add validates_presence_of_amount in the Contributions model.

class Gift < ActiveRecord::Base
  has_many :contributions
  accepts_nested_attributes_for :contributions
  ...
end

class Contribution < ActiveRecord::Base
  validates_presence_of :amount
  ...
end

Answer 2

class Gift < ActiveRecord::Base
  has_many :contributions
  accepts_nested_attributes_for :contributions,
    :reject_if => proc { |a| a['amount'].blank? }
end

class Contribution < ActiveRecord::Base
  belongs_to :gift
  validates_presence_of :nickname, :amount
end

...in the gift form...

f.text_field :nickname, :value => (params[:gift][:contributions_attributes]['0'][:nickname] rescue @m.full_name)

This preserves :nickname changes through failed validations and still discards a nested contributions that contain :nickname only.