Rails core - Jul 2008 - unintuitive behaviour of AssocationCollection#first

A post on rails-talk led me to worry about the following:

post.comments.first.title = ''Foo''
post.comments.collect &:author #this line isn''t really important -
anything that requires loading the collection will do

Ta-da! post.comments.first.title reverts to its old value (because  
it''s now a different object - the first item of the freshly loaded  
collection as opposed to just the result of find :first).
This behaviour is rather unintuitive to me (and I would have thought  
conducive to hard to track down bugs) - Thoughts?


Fred

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> identity map ?
It''s a way of guaranteeing that there''s only one object with a
given
id in a given context:

http://martinfowler.com/eaaCatalog/identityMap.html




-- 
Cheers

Koz

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On 22 Jul 2008, at 10:41, Michael Koziarski wrote:
>
>> identity map ?
>
> It''s a way of guaranteeing that there''s only one object
with a given
> id in a given context:
>
> http://martinfowler.com/eaaCatalog/identityMap.html
>
Ah yes. I had an inkling that might be what you were talking about.  
That itself might introduce some subtle differences in behaviour

Fred

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> Ah yes. I had an inkling that might be what you were talking about.
> That itself might introduce some subtle differences in behaviour
It introduces huge differences in behaviour for some situations like:

def whatever
  @foo = Foo.find(1)
  # Some other process updates foo 1
  @foos = Foo.find(:all) # do you retain the old data for foo#1 or
replace it with the new data, or raise an exception?
end

The first part of an identity map is easy, it''s defining the behaviour
in all the edge cases that makes it hard, :)
-- 
Cheers

Koz

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On 22 Jul 2008, at 10:52, Michael Koziarski wrote:
>
>> Ah yes. I had an inkling that might be what you were talking about.
>> That itself might introduce some subtle differences in behaviour
>
> It introduces huge differences in behaviour for some situations like:
>
> def whatever
>  @foo = Foo.find(1)
>  # Some other process updates foo 1
>  @foos = Foo.find(:all) # do you retain the old data for foo#1 or
> replace it with the new data, or raise an exception?
> end
>
> The first part of an identity map is easy, it''s defining the
behaviour
> in all the edge cases that makes it hard, :)
That''s a bit of a bastard :-) It''s not even that much of an
edge case.

Fred

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