Dirty checking is broken for string join
Reported by quake wang | July 13th, 2008 @ 04:14 AM | in 2.x
Rails 2.1:
create_table :topics do |t|
t.string :title
end
class Topic < ActiveRecord::Base
end
in console:
>> t = Topic.find(1)
>> t.title = t.title << "new"
>> t.changed?
=> false
Comments and changes to this ticket
-
-
Jason Dew July 14th, 2008 @ 07:09 PM
This is the same problem as http://rails.lighthouseapp.com/p...
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Tom Ward July 25th, 2008 @ 12:26 PM
This ticket is invalid. Dirty checking will only currently work if you replace an attribute with a new value, not edit it in place.
Instead you should do:
t = Topic.find(1) t.title_will_change! t.title = t.title << "new" t.changed? # => true -
Clemens Kofler July 25th, 2008 @ 02:22 PM
- → Tag changed from “” to “activerecord”
I agree with Tom. It is known that all changes that don't go through standard assignment with = will not mark the attribute as changed.
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quake wang July 26th, 2008 @ 02:26 AM
I know will_change can resolve this issue as a temp solution, however, how to explain the inconsistent of string / numeric field?
create_table :topics do |t|
t.string :title
t.integer :score
end
t = Topic.find(1)
t.title = t.title.contact(33)
t.changed?
- => false
t.score = t.score.*(33)
t.changed?
- => true
-
Tom Ward July 26th, 2008 @ 10:30 AM
What does t.title.contact(33) do?
If you set the title to the same value it was before, changed? will return false.
If you set it to a new value, it should return true.
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Clemens Kofler July 26th, 2008 @ 03:29 PM
I've tested this and I can confirm it.
A little something to think about before someone actually spends time on creating a patch that isn't really necessary:
With t.title << "new", I would actually think that the title changes. t.title = t.title << "new" looks intriguing to me because it looks like it does the actual assignment twice. IMO you shouldn't "reassign" the variable when using the << operator.
What would make sense, though, is having something like t.title = t.title + "new" or its short form, t.title += "new". Both of them actually work perfectly fine and t.title_changed? returns true.
The important question to ask is whether one should use something misleading like t.title = t.title << "new" when there's two valid ways around that even look more logical. One is, as I said, t.title += "new" and the other would be to use t.title_will_change! t.title << "new".
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Zach Holman July 31st, 2008 @ 09:00 PM
I can confirm this as well.
There's some discussion on whether something is "changed" if the contents are changed. To me that seems like a valid case. I was working on a serialized array to a model, and if I do something like:
@
my_model.serialized_array << 'new pushed element'
my_model.changed # intuitively this should return ["serialized_array"]
@
I feel that this is a common scenario where a serialized array needs modification, and the very idea of something being modified is, well, a change.
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