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

1. what does (&:id) do after .map

   @user_cnae_classifications = user.cnae_classifications.map(&:id)
   

   what is the difference of .map with it and without it?

2. in this method call:

   UserCnaeClassification.create(
     user: @user,
     cnae_classification_id: id
   )
   

   How do I read that part of the code...

   user: @user,
   cnae_classification_id: id
   

   are they keys and values?

CodePudding user response：

1 ) You should read some tutorials on map to get acquainted.

2 ) The #create method can accept a key-value hash of known attributes (known to the class in question, in this case that is UserCnaeClassification) to assign upon creation. So you're basically right, they are key-value pairs but they are specific to this class/object. Those same keys might not work on another class/object. Additional reading:

Usage: Also pluck doesn't work with regular Arrays.