Good afternoon people. I’m new to Rails and I’m using google translate to post here in English.

My question is not an error, it is for understanding. As I’m new to Rails, I can’t read all the code yet.

I would like to understand 2 points in this class that is in “Services”:

class SaveUserCnaeClassifications
  def initialize(user, cnae_classifications)
    @user = user
    @cnae_classifications = cnae_classifications
    @user_cnae_classifications = user.cnae_classifications.map(&:id)
  end

  def call
    return if @cnae_classifications.nil?
    
    array_delete = @user_cnae_classifications.difference(@cnae_classifications)
    delete(array_delete)

    array_add = @cnae_classifications.difference(@user_cnae_classifications)
    add(array_add)
  end
 
  private
  def add(cnae_classifications_ids)
    cnae_classifications_ids.each do |id|
      UserCnaeClassification.create(
        user: @user,
        cnae_classification_id: id
      )
    end
  end

  def delete(cnae_classifications_ids)
    cnae_classifications_ids.each do |id|
      UserCnaeClassification.where(user: @user, cnae_classification_id: id)
                            .first
                            .destroy
    end
  end
end

1 – what does “(&:id) do after .map
what is the difference of .map with it and without it?

2 – in the method:

def add(cnae_classifications_ids)
  cnae_classifications_ids.each do |id|
    UserCnaeClassification.create(
      user: @user,
      cnae_classification_id: id
    )
  end
end

How do I read that part of the code…

user: @user,
cnae_classification_id: id

are they keys and values?

Thank you for your attention and I apologize for the basic questions.