如何验证兄弟姐妹名称属性的唯一性？

Question

I have Category model with tree structure via ancestry gem. I'd like siblings to have unique names, for example:

Books:
  Science
  science (not valid)

But

Books:
  Science
  Children:
    Science (valid)

How can I setup this validation?

Answer 1

You can use Rails validate uniqueness with scope defined.

For example let's say you have a column called parent_id then your validation would look like

validates :name, uniqueness: { scope: :parent_id }

Answer 2

You can write your own validator using ActiveRecord validate to check the childrens of the parent record like:

class Category < ApplicationRecord
  has_ancestry
  validate :children_name_is_unique

  def children_name_is_unique
    return unless parent.try(:has_children?)
    if Category.where(id: parent.child_ids, name: name).exists?
      errors.add(:name, 'Duplicate children name')
    end
  end
end