class ActiveRecord::Associations::CollectionProxy

def replace(other_array)

# => ActiveRecord::AssociationTypeMismatch: Pet expected, got String
person.pets.replace(["doo", "ggie", "gaga"])

an ActiveRecord::AssociationTypeMismatch error:
If the supplied array has an incorrect association type, it raises

# => [#]
person.pets

person.pets.replace(other_pets)

other_pets = [Pet.new(name: 'Puff', group: 'celebrities')]

# => [#]
person.pets

end
has_many :pets
class Person < ActiveRecord::Base

and delete/add only records that have changed.
Replaces this collection with +other_array+. This will perform a diff 
def replace(other_array)
  @association.replace(other_array)
end