#990 association#build inconsistency - Ruby on Rails

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#990 ✓resolved

association#build inconsistency

Reported by Mathijs Kwik | September 7th, 2008 @ 11:22 PM | in 3.x

When building an object through an association, the resulting object isn't bound to the proxy owner if the proxy owner is a new record. If the proxy owner is already saved, it is bound.

I think this is inconsistent.

This also boils down to using find_or_initialize_by or find_or_create_by on associations on new records.


class User < ActiveRecord::Base
  has_many :posts, :dependent => :destroy
end

class Post < ActiveRecord::Base
  belongs_to :user
end

>> u=User.first
=> #<User id: 1, name: "user 1", created_at: "2008-09-07 22:07:35", updated_at: "2008-09-07 22:07:35">
>> u2=User.new
=> #<User id: nil, name: nil, created_at: nil, updated_at: nil>

>> u.posts.build.user
=> #<User id: 1, name: "user 1", created_at: "2008-09-07 22:07:35", updated_at: "2008-09-07 22:07:35">
>> u2.posts.build.user
=> nil

>> u.posts.find_or_initialize_by_title('title').user
=> #<User id: 1, name: "user 1", created_at: "2008-09-07 22:07:35", updated_at: "2008-09-07 22:07:35">
>> u2.posts.find_or_initialize_by_title('title').user
=> nil

Comments and changes to this ticket

Pratik December 20th, 2008 @ 03:32 PM
- Assigned user set to “Michael Koziarski”
- State changed from “new” to “wontfix”
Please reopen once we have a patch for this.

This looks similar to an ID map patch Koz has been involved with, so assigning the ticket to him.
Prem Sichanugrist (sikachu) February 1st, 2009 @ 06:24 AM
I just wonder ..

I've looked at the code, and I found out that the association's build method is done by setting foreign_key to be the parent's id. Can we also do something like set the attribute with the name of the parent object to be refer to parent object?
Ryan Bigg April 29th, 2010 @ 12:52 AM
- State changed from “wontfix” to “open”
Marked a similar ticket, #4497, as a duplicate of this one and asked the user to submit a patch here.
You flagged this item as spam.
Evgeniy Dolzhenko April 29th, 2010 @ 07:08 AM
Btw. shouldn't :inverse_of association options handle this?
Jeremy Kemper May 4th, 2010 @ 06:48 PM
- Milestone changed from “2.x” to “3.x”
[bulk edit]
You flagged this item as spam.
Andreas Mayer July 31st, 2010 @ 12:05 AM
Have the same problem. Using the workaround. Will this be fixed in Rails 3 final?

Neeraj Singh August 13th, 2010 @ 03:03 PM

State changed from “open” to “resolved”
Importance changed from “” to “Low”

As Evgeniy Dolzhenko suggested setting inverse_of resolves the issue.

class Car < ActiveRecord::Base
  has_many :brakes, :inverse_of => :car
end

class Brake < ActiveRecord::Base
  belongs_to :car, :inverse_of => :brakes
end

> Car.first.brakes.build.car
  Car Load (0.4ms)  SELECT "cars".* FROM "cars" LIMIT 1
 => #<Car id: 1, name: nil> 

> Car.new.brakes.build.car
 => #<Car id: nil, name: nil> 

> Car.create.brakes.build.car
  SQL (0.5ms)  INSERT INTO "cars" ("name") VALUES (NULL)
 => #<Car id: 2, name: nil>


> Car.last.brakes.find_or_initialize_by_name('cool').car
  Car Load (0.6ms)  SELECT "cars".* FROM "cars" ORDER BY cars.id DESC LIMIT 1
  Brake Load (0.2ms)  SELECT "brakes".* FROM "brakes" WHERE ("brakes".car_id = 2) AND ("brakes"."name" = 'cool') LIMIT 1
  Car Load (0.1ms)  SELECT "cars".* FROM "cars" WHERE ("cars"."id" = 2) LIMIT 1
 => #<Car id: 2, name: nil> 

> Car.last.brakes.find_or_create_by_name('cool').car
  Car Load (0.4ms)  SELECT "cars".* FROM "cars" ORDER BY cars.id DESC LIMIT 1
  Brake Load (0.3ms)  SELECT "brakes".* FROM "brakes" WHERE ("brakes".car_id = 2) AND ("brakes"."name" = 'cool') LIMIT 1
  SQL (0.3ms)  INSERT INTO "brakes" ("car_id", "name") VALUES (2, 'cool')
 => #<Car id: 2, name: nil>

tested with rails edge.