Some refacto for new_catgory_integration

update_or_create_category.rb

def update_or_create_expert_category(category_ids)
  categories = Category.find(category_ids.reject {|x| x.empty?})

  @expert.categories.each do |category|
    unless categories.include? category
      expert_category.destroy
    end
    unless @expert.categories.include? category
      ExpertCategory.create(expert: @expert, category: category)
    end
  end
end

i don't like putting some ruby code inside the reject parameter
categories = Category.find(category_ids.reject {|x| x.empty?})

I prefere something like:

ids = category_ids.reject {|x| x.empty?}
categories = Category.find(ids)

I think it's cleaner.

For the rest, ok, even though, I have the feeling we can make this clearer.