How to enter unique associations only?

Question

Running the following code to add an association enters multiple entries each time the code is ran:

store.categories << category

Is there a way to make it only enter unique associations between the two models in the db?

Answer 1

Directly from the rails guides, hope it helps:

class Person
  has_many :readings
  has_many :posts, :through => :readings, :uniq => true
end

Answer 2

Ignoring duplicates only seem to work with begin and rescue logic:

begin
  stores.categories << category
rescue
  puts "Duplicate entry ignored"
end