Implemented Quantity

app/models/quantity.rb

@@ -1,2 +1,13 @@
 class Quantity < ActiveRecord::Base
+  enum domain: {
+    diet: 0,
+    measurement: 1,
+    exercise: 2
+  }
+
+  belongs_to :project
+
+  validates :project, associated: true
+  validates :name, presence: true, uniqueness: {scope: :project_id}
+  validates :domain, inclusion: {in: domains.keys}
 end