Metaprogramming eg

meta.rb

# Permission based relations  
# define admins, uploaders and guests associations via users
%w(admins uploaders guests).each do |method_name|
  define_method(method_name) { self.memberships.where(role: method_name.singularize).collect(&:user) }
end

## vs...

def admins
  self.memberships.where(role: :admin).collect(&:user)
end

def uploaders
  self.memberships.where(role: :upload).collect(&:user)
end

def guests
  self.memberships.where(role: :guest).collect(&:user)
end