def serialize_categories
      serialized = {}
      categories.each do |category|
        serialized[category.id] = category.serialize_base
      end
      serialized
    end
def serialize_categories
      serialized = {}
      categories.each do |category|
        serialized[category.id] = category.serialize_base
      end
      serialized
    end
This function serializes the list of categories for the post.