How to add an attribute to User reference I would need to add an attribute to a user_reference field that "explains" the type of relationship.

Example:
My users are music players and the play in different groups.
The same user can play guitar in one group and the bass in another group.

Groups are my nodes and I can link them with the players. While I am linking them, I would also like to set the instruments they play in that group.

Group 1 - Player1|guitar
Group 2 - Player1|bass
Group 3 - Player2|guitar

Probably a way to do that is using "field collection"; is there another way?
Alternatives could be Paragraphs, Multifield, Inline Entity Form or Double Field.