Rails - Jun 2010 - Is it possible to temporary cache an attribute's value in memory or do something similar?

Hello,

I have a bit of code that depicts this hypothetical setup below. A
class Foo which contains many Bars. Bar belongs to one and only one
Foo. At some point, Foo can do a finite loop that lapses 2+
iterations. In that loop, something like the following happens:

    bar = Bar.find_where_in_use_is_zero
    bar.in_use = 1

Basically what find_where_in_use_is_zero does something like this in
as far as SQL goes:

``SELECT * from bars WHERE in_use = 0``

Now the problem I''m facing is that I cannot run the following line of
code after bar.in_use =1 is invoked:

    bar.save

The reason is clear, I''m still looping and the new Foo hasn''t
been
created, so we don''t have a foo_id to put into bars.foo_id. Even if I
set to allow foo_id to be NULL, we have a problem where one of the
bars can fail validation and the existing one was saved to the
database. In my application, that doesn''t work. The entire request is
atomic, either all succeeds or fails together. What happens next, is
that in my loop, I have the potential to select the same exact bar
that I did on a previous iteration of the loop since the in_use flag
will not be set to 1 until @foo.save is called.

Is there anyway to work around this condition and temporarily set the
in_use attribute to 1 for subsequent iterations of the loop so that I
retrieve an available bar instance?

Thanks,

Matthew

-- 
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
To unsubscribe from this group, send email to
rubyonrails-talk+unsubscribe-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk?hl=en.

On Jun 2, 12:18 am, Matthew Hillsborough
<matthew.hillsboro...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> Is there anyway to work around this condition and temporarily set the
> in_use attribute to 1 for subsequent iterations of the loop so that I
> retrieve an available bar instance?
>
Well if things do need to be atomic then you probably want to wrap
this in a transaction and roll back if one of those validations fail.
You could also change your conditions on that find to exclude a bar
with a particular id

Fred
> Thanks,
>
> Matthew
-- 
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
To unsubscribe from this group, send email to
rubyonrails-talk+unsubscribe@googlegroups.com.
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk?hl=en.