Postgresql error when using Rails' uniq method

I have an Item model that belongs to a Product model. Product has a properties column of hstore type. I want to return a set of unique items that belong to a product, and that do not include the current item: @item.similar_items

class Item < ActiveRecord::Base
  belongs_to :product
  scope :by_platform, ->(value) { joins(:product).merge(Product.by_platform(value)) }
  scope :by_genre, ->(value) { joins(:product).merge(Product.by_genre(value)) }

  def similar_items
    Item.includes(:product)
      .by_platform(self.product_platform)
      .by_genre(self.product_genre)
      .limit(3).where.not(product: self.product)
      .order("(properties -> 'release_date')::date DESC")
      .uniq
  end
end

class Product < ActiveRecord::Base
  store_accessor :properties, :platform, :genre
  has_many :items

  scope :by_platform, ->(value) { where("properties @> hstore('platform', ?)", value) }
  scope :by_genre, ->(value) { where("properties @> hstore('genre', ?)", value) }
end

Error:

PG::Error: ERROR:  for SELECT DISTINCT, ORDER BY expressions must appear in select list
LINE 1: ...e')) AND ("items"."product_id" != 426)  ORDER BY (properties...