Moving to github

app/models/collection.rb

@@ -0,0 +1,47 @@
+class Collection < ApplicationRecord
+  # Associations
+  belongs_to :user
+  belongs_to :parent_collection, class_name: "Collection", optional: true
+  has_many :subcollections, class_name: "Collection", foreign_key: "parent_collection_id", dependent: :destroy
+  has_many :collection_games, dependent: :destroy
+  has_many :games, through: :collection_games
+
+  # Validations
+  validates :name, presence: true
+  validate :cannot_be_own_parent
+  validate :subcollection_depth_limit
+
+  # Scopes
+  scope :root_collections, -> { where(parent_collection_id: nil) }
+
+  # Instance methods
+  def game_count
+    games.count
+  end
+
+  def total_game_count
+    game_count + subcollections.sum(&:total_game_count)
+  end
+
+  def root?
+    parent_collection_id.nil?
+  end
+
+  def subcollection?
+    parent_collection_id.present?
+  end
+
+  private
+
+  def cannot_be_own_parent
+    if parent_collection_id.present? && parent_collection_id == id
+      errors.add(:parent_collection_id, "cannot be itself")
+    end
+  end
+
+  def subcollection_depth_limit
+    if parent_collection.present? && parent_collection.parent_collection.present?
+      errors.add(:parent_collection_id, "cannot nest more than one level deep")
+    end
+  end
+end