ActiveRecord "column"_changed? method issue with nil values

[fabn]

I'm using CarrierWave backgrounder which relies on xxx_changed? method to enqueue processing jobs. In a failing test I discovered this CW behavior which triggers background jobs when files are not present at all.

Given this class

class Source < ActiveRecord::Base
  # CarrierWave integration for logos
  mount_uploader :logo, LogoUploader
end

the following happens

[12] pry(main)> s = Source.new
+----+------+---------+------+------------+------------+
| id | name | website | logo | created_at | updated_at |
+----+------+---------+------+------------+------------+
|    |      |         |      |            |            |
+----+------+---------+------+------------+------------+
1 row in set
[13] pry(main)> s.logo_changed?
false
[14] pry(main)> s.logo = nil
nil
[15] pry(main)> s.logo_changed?
true
[16] pry(main)> s.changes
{
    "logo" => [
        [0] #<LogoUploader:0x007fcc972db7a0 @model=#<Source id: nil, name: nil, website: nil, logo: nil, created_at: nil, updated_at: nil>, @mounted_as=:logo>,
        [1] #<LogoUploader:0x007fcc95a7d460 @model=#<Source id: nil, name: nil, website: nil, logo: nil, created_at: nil, updated_at: nil>, @mounted_as=:logo>
    ]
}

[fabn]

Another weird behavior:

[1] pry(main)> s = Source.create!(name: 'foo', website: 'http://www.example.com', remote_logo_url: '')
+----+------+------------------------+------+-------------------------+-------------------------+
| id | name | website                | logo | created_at              | updated_at              |
+----+------+------------------------+------+-------------------------+-------------------------+
| 1  | foo  | http://www.example.com |      | 2015-02-24 14:42:52 UTC | 2015-02-24 14:42:52 UTC |
+----+------+------------------------+------+-------------------------+-------------------------+
1 row in set
[2] pry(main)> s.previous_changes[:logo] # !!! should be nil
[
    [0] #<LogoUploader:0x007fa7fb932880 @model=#<Source id: 1, name: "foo", website: "http://www.example.com", logo: nil, created_at: "2015-02-24 14:42:52", updated_at: "2015-02-24 14:42:52">, @mounted_as=:logo>,
    [1] #<LogoUploader:0x007fa7fb9329e8 @model=#<Source id: 1, name: "foo", website: "http://www.example.com", logo: nil, created_at: "2015-02-24 14:42:52", updated_at: "2015-02-24 14:42:52">, @mounted_as=:logo, @storage=#<CarrierWave::Storage::File:0x007fa7fb9251d0 @uploader=#<LogoUploader:0x007fa7fb9329e8 ...>>>
]

[fabn]

I created a couple of failing specs for this in https://github.com/fabn/carrierwave/tree/issue-1571

I can try to fix them if you think this is an actual issue

[bensie]

@fabn If you can work up a fix for this that would be great! Looks valid to me.

We're piggy-backing on ActiveModel::Dirty as best we can, but there are definitely cases where it falls apart. You'll see when you dig in that we call send(:"\#{column}_will_change!") where appropriate, but I wouldn't be surprised at all if there are some holes in that.

[avgerin0s]

@fabn @bensie I'm trying to tackle this issue. You may take a look at the #1635 PR

[fabn]

@eavgerinos I'll try it as soon as I have some spare time. If this works is there any ETA for a rubygems release? I don't like to use github in Gemfile for production stuff.