I’m creating an app which has two models - bands and users. A
relationship between users and bands in many to many.
However, when I’m adding an existing to user to a band (ie. updating
the bands_users table) how can i check if the relationship between the
user and the band already exists? For example, if a user with ID of 3
was already a member of a band with ID 5, and then somebody tried to
make this connection again - I want to output an error message. Is
there some special validation I can place in a bands_users.rb that
validated the uniqueness of the entire record?