Ruby/Rails Collection to Collection

Question

I have a two tables joined with a join table - this is just pseudo code:

Library
Book
LibraryBooks

What I need to do is if i have the id of a l

Answer 1

Perhaps:

l.books.map {|b| b.libraries}

or

l.books.map {|b| b.libraries}.flatten.uniq

if you want it all in a flat array.

Of course, you should really define this as a method on Library, so as to uphold the noble cause of encapsulation.