Active record associations


#1

What’s wrong with ruby associations?

Somehow association fields don’t have any support for dirty objects
nor optimistic locking.

I would expect dirty objects to work like this:

class Person
has_many :cars
end

person = Person.find_by_name(“Jack”)
person.cars

=> [#<Car id: 2, name: “BMW”, created_at: “2008-11-04 03:04:46”,
updated_at: “2008-11-04 03:04:46”>]

person.cars=[Car.find_by_name(“Porsche”), Car.find_by_name(“VW”)]
person.cars

=> [#<Car id: 1, name: “Porsche”, created_at: “2008-11-04 03:04:46”,
updated_at: “2008-11-04 03:04:46”>, #<Car id: 3, name: “VW”,
created_at: “2008-11-04 03:04:46”, updated_at: “2008-11-04 03:04:46”>]

person.changed?
=> true

person.changes

=> {“cars”=>[[#<Car id: 2, name: “BMW”, created_at: “2008-11-04
03:04:46”, updated_at: “2008-11-04 03:04:46”>], [#<Car id: 1, name:
“Porsche”, created_at: “2008-11-04 03:04:46”, updated_at: “2008-11-04
03:04:46”>, #<Car id: 3, name: “VW”, created_at: “2008-11-04
03:04:46”, updated_at: “2008-11-04 03:04:46”>]]}

person.save #associations are saved in the database

However ror returns the following

person = Person.find_by_name(“Jack”)
person.cars

=> [#<Car id: 2, name: “BMW”, created_at: “2008-11-04 03:04:46”,
updated_at: “2008-11-04 03:04:46”>]

person.cars=[Car.find_by_name(“Porsche”), Car.find_by_name(“VW”)] #associations are saved in the database
person.cars

=> [#<Car id: 1, name: “Porsche”, created_at: “2008-11-04 03:04:46”,
updated_at: “2008-11-04 03:04:46”>, #<Car id: 3, name: “VW”,
created_at: “2008-11-04 03:04:46”, updated_at: “2008-11-04 03:04:46”>]

person.changed?
=> false

person.changes

=> {}

The same problem happens with optimistic locking

p1 = Person.find_by_name(“Jack”)
p2 = Person.find_by_name(“Jack”)

p1.cars = [Car.find_by_name(“Porsche”)]
p1.save

p2.cars = [Car.find_by_name(“BMW”)]
p2.save

I would expect the object to raise an exception, but it doesn’t.

Isn’t there a way to unify the behaviour of regular fields and
associations? Most objects in my app don’t represent flat tables, but
tables that associate each other. Right now I’m forced to having to
wrap many attribute updates into a transaction and write my own object
comparisons.