Quantities index WIP

app/models/quantity.rb

@@ -0,0 +1,35 @@
+class Quantity < ApplicationRecord
+  belongs_to :user, optional: true
+  belongs_to :parent, optional: true, class_name: "Quantity"
+  has_many :subquantities, class_name: "Quantity", inverse_of: :parent,
+    dependent: :restrict_with_error
+
+  validate if: ->{ parent.present? } do
+    errors.add(:parent, :user_mismatch) unless user == parent.user
+  end
+  validates :name, presence: true, length: {maximum: type_for_attribute(:name).limit}
+  validates :description, length: {maximum: type_for_attribute(:description).limit}
+
+  scope :defaults, ->{ where(user: nil) }
+  scope :ordered, ->{
+    left_outer_joins(:parent).order(ordering)
+  }
+
+  def self.ordering
+    [arel_table.coalesce(Arel::Table.new(:parents_quantities)[:name], arel_table[:name]),
+     arel_table[:parent_id].not_eq(nil),
+     :name]
+  end
+
+  def to_s
+    name
+  end
+
+  def movable?
+    subunits.empty?
+  end
+
+  def default?
+    parent_id.nil?
+  end
+end