Validations on nested attributes fail on nil foreign key on object creation

Daniele try this it will fix above problem.

class Tag
  belongs_to :post,:inverse_of => :post_tags
  validates_presence_of :post
end

class Post
  has_many :post_tags, :inverse_of => :post
  accepts_nested_attribute_for :post_tags
end

Solution proposed by Subba works for me. Marking it as resolved. If it is still an issue then let's discuss.