Question

Note: This question was spawned from another question I had regarding the use of accepts_nested_attributes_for. You may reference that question for additional context, if needed.

I believe this question is best explained with a simple example:

class Foo < ActiveRecord::Base
  has_many :bars, inverse_of: :foo
end

class Bar < ActiveRecord::Base
  validates :foo_id, presence: true

  belongs_to :foo, inverse_of: :bars
end

f = Foo.new()
=> #<Foo id: nil, created_at: nil, updated_at: nil>
b = f.bars.build()
=> #<Bar id: nil, foo_id: nil, created_at: nil, updated_at: nil>
f.save!
=> ActiveRecord::RecordInvalid: Validation failed: Bars foo can't be blank

Is there an easy way to fix this problem? I know that I could save f first and then build b, but my situation is a little more complex than this example (see the question I referenced above) and I’d prefer to avoid that if possible.

Answer 1

The child records get created at the same time as parent, this is why your validation is failing, your child is not yet persisted. to make it work i would write a custom validation like this

class Foo < ActiveRecord::Base
  has_many :bars
  accepts_nested_attributes_for :bars, :allow_destroy => true

end

class Bar < ActiveRecord::Base
  belongs_to :foo
  validates_presence_of :bar
end