Rails - Jan 2007 - Best way to update attributes on AR objects without saving?

All,

In some cases, one may not want to save attributes retrieved from a form
to the database right away.  Would the best way to bulk update your AR
object from the params hash be to do:

@ar_obj.attributes.merge!(params[:appropriate_key])

?  This seems to be the the best approach to me.

For some reason, I was under the impression that update_attributes
didn''t update the record in the database and so now I''m trying
to find
the appropriate replacement.

Thanks,
Wes

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How about:

@ar_obj = ArObj.new(params[:id])
if @ar_obj.valid?
  # whatever code you need here for good objects
  @ar_obj.save
else
  # whatever code you have for erroneous information
end

AR is smart enough to figure out whether a record already exists by primary
key, so save will INSERT if it''s a new record or UPDATE if
it''s an existing
one. Updating attributes skips straight to the database before giving you a
look. That''s why creating from the params has is so powerful.

So what if you don''t have a params hash? Make one:

@ar_obj = ArObj.new({:id => 3, :title = ''yippie skippy''})

Yes?


athem wrote:
> 
> 
> All,
> 
> In some cases, one may not want to save attributes retrieved from a form
> to the database right away.  Would the best way to bulk update your AR
> object from the params hash be to do:
> 
> @ar_obj.attributes.merge!(params[:appropriate_key])
> 
> ?  This seems to be the the best approach to me.
> 
> For some reason, I was under the impression that update_attributes
> didn''t update the record in the database and so now I''m
trying to find
> the appropriate replacement.
> 
> Thanks,
> Wes
> 
> -- 
> Posted via http://www.ruby-forum.com/.
> 
> > 
> 
> 
-- 
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Wes Gamble wrote:
> All,
> 
> In some cases, one may not want to save attributes retrieved from a form
> to the database right away.  Would the best way to bulk update your AR
> object from the params hash be to do:
> 
> @ar_obj.attributes.merge!(params[:appropriate_key])
@ar_obj.attributes = params[:appropriate_key]

is all you need. The only attributes set are those named
by keys in the params hash.

-- 
We develop, watch us RoR, in numbers too big to ignore.


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Mark Reginald James wrote:
> @ar_obj.attributes = params[:appropriate_key]
> 
> is all you need. The only attributes set are those named
> by keys in the params hash.
Shouldn''t you merge the keys, given the possibility that your object
may
have an unsaved attribute set already (that you want to keep) that is 
not represented in your params hash.  Using = will blow away those 
attributes, but merge! will preserve them.

Thanks,
Wes

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Wes Gamble wrote:
> Mark Reginald James wrote:
> 
>> @ar_obj.attributes = params[:appropriate_key]
>>
>> is all you need. The only attributes set are those named
>> by keys in the params hash.
> 
> Shouldn''t you merge the keys, given the possibility that your
object may
> have an unsaved attribute set already (that you want to keep) that is 
> not represented in your params hash.  Using = will blow away those 
> attributes, but merge! will preserve them.
No, the attributes= method does not assign a new attribute hash.
It just assigns new values to the attributes (and attr_accessors)
keyed in the RHS hash.

-- 
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On 1/20/07, Wes Gamble
<rails-mailing-list-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org>
wrote:
>
> Mark Reginald James wrote:
>
> > @ar_obj.attributes = params[:appropriate_key]
> >
> > is all you need. The only attributes set are those named
> > by keys in the params hash.
>
> Shouldn''t you merge the keys, given the possibility that your
object may
> have an unsaved attribute set already (that you want to keep) that is
> not represented in your params hash.  Using = will blow away those
> attributes, but merge! will preserve them.
Actually it doesn''t blow them away.  That''s something that I
forget
every single time I use it.

Also, because merge! is a method on Hash, using that will bypass
things like attr_protected, which you don''t want.

Pat

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OK I''m convinced.  I had tested using "=" instead of merge!
and I had
convinced myself that "=" would blow away keys.  But I just retested
it
and it works as described.  I must have made a mistake on the first 
test.

Interestingly (well, maybe not...) enough, I was attempting to use 
merge! and I could not get it to work to copy a params hash into an 
attribute hash,  even though I verified the existence of the same keys 
(of the same "type") in the two hashes, and I was able to copy the 
values across fine if I used an interator on the params hash.

I recalled that the params hash is a HashWithIndifferentAccess and the 
attributes Hash is a regular Hash - maybe that has something to do with 
it.  Weird.

Wes


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