Rails - Nov 2005 - update_attribute send updates every field, why?

Hi,

If you do model.update_attribute("fname", "John") the every
field is
updated, it generates a big update statement like:

update persons set fname=x, lname=y, email=z, whatever=blah, 
and_stuff=stuff where id=1

I would think it would just generate:
update persons set fname=''John'' where id=1

Anybody know why AR acts this way?

Jeroen

Jeroen Houben wrote:
> Hi,
> 
> If you do model.update_attribute("fname", "John") the
every field is
> updated, it generates a big update statement like:
> 
> update persons set fname=x, lname=y, email=z, whatever=blah, 
> and_stuff=stuff where id=1
> 
> I would think it would just generate:
> update persons set fname=''John'' where id=1
> 
> Anybody know why AR acts this way?
I think that''s just the Rails does it.  Records are always
saved in their entirety.

I''ve found the following simple Active Record extentions to be
helpful in cutting out some useless database activity:


class ActiveRecord::Base
   def changed(attrs)
     return false if attrs.nil?
     self.class.content_columns.each { |c| return true if self[c] != attrs[c] }
     return false
   end

   def update_attributes_if_changed(attrs)
     changed(attrs) ? update_attributes(attrs) : true
   end

   def update_attribute_if_changed(name, value)
     self[name] != value ? update_attribute(name, value) : true
   end
end


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

Mark Reginald James wrote:
> Jeroen Houben wrote:
> 
>> Hi,
>>
>> If you do model.update_attribute("fname", "John")
the every field is
>> updated, it generates a big update statement like:
>>
>> update persons set fname=x, lname=y, email=z, whatever=blah, 
>> and_stuff=stuff where id=1
>>
>> I would think it would just generate:
>> update persons set fname=''John'' where id=1
>>
>> Anybody know why AR acts this way?
> 
> 
> I think that''s just the Rails does it.  Records are always
> saved in their entirety.
> 
> I''ve found the following simple Active Record extentions to be
> helpful in cutting out some useless database activity:
> 
> 
> class ActiveRecord::Base
>   def changed(attrs)
>     return false if attrs.nil?
>     self.class.content_columns.each { |c| return true if self[c] != 
> attrs[c] }
>     return false
>   end
> 
>   def update_attributes_if_changed(attrs)
>     changed(attrs) ? update_attributes(attrs) : true
>   end
> 
>   def update_attribute_if_changed(name, value)
>     self[name] != value ? update_attribute(name, value) : true
>   end
> end
> 
> 
This doesn''t address my original problem though, right? I mean in the 
end you still call  update_attribute which generates the full update 
SQL, not just for one field. Or am I missing something here...

Jeroen

Jeroen Houben wrote:
> This doesn''t address my original problem though, right? I mean in
the
> end you still call  update_attribute which generates the full update 
> SQL, not just for one field. Or am I missing something here...
Yes, as I wrote, unless you do custom SQL, Rails always saves entire records.
The code I gave was just a way to cut out unnecessary saves in certain
circumstances.

I''m not sure whether entire records are saved to simplify the Rails
code,
or because of some tricky issues that would arise if attributes could
be updated individually.  At the least you''d probably have to add a
dirty
bit to each record, or to each attribute in each record.

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

I too am observing this. Can anyone throw some light on this behaviour?

-----Original Message-----
From: rails-bounces-1W37MKcQCpIf0INCOvqR/iCwEArCW2h5@public.gmane.org
[mailto:rails-bounces-1W37MKcQCpIf0INCOvqR/iCwEArCW2h5@public.gmane.org] On
Behalf Of Jeroen Houben
Sent: Thursday, November 17, 2005 5:23 PM
To: rails-1W37MKcQCpIf0INCOvqR/iCwEArCW2h5@public.gmane.org
Subject: [Rails] update_attribute send updates every field, why?

Hi,

If you do model.update_attribute("fname", "John") the every
field is
updated, it generates a big update statement like:

update persons set fname=x, lname=y, email=z, whatever=blah, 
and_stuff=stuff where id=1

I would think it would just generate:
update persons set fname=''John'' where id=1

Anybody know why AR acts this way?

Jeroen
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Rails-1W37MKcQCpIf0INCOvqR/iCwEArCW2h5@public.gmane.org
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>From ActiveRecord::Base:
     def update_attribute(name, value)
        send(name.to_s + ''='', value)
        save
      end
     def save
        raise ActiveRecord::ReadOnlyRecord if readonly?
        create_or_update
      end

The call to ''create_or_update'' will trigger either
object#create or
object#update, each of which contains the SQL code that persists the
attributes in the object. You could probably   override
update_attribute, and have it call a new method
''create_or_update_lone_attribute'' instead of
''save''. Doesnt look like
that would break anything.

On the other hand, why? Unless you have some huge binary columns, the
db will update n columns in a record just about as quick as a single
column.

cheers
Gerret

On 12/23/05, GeekEntrepreneu
<geekentrepreneur-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
> I too am observing this. Can anyone throw some light on this behaviour?
>
> -----Original Message-----
> From: rails-bounces-1W37MKcQCpIf0INCOvqR/iCwEArCW2h5@public.gmane.org
> [mailto:rails-bounces-1W37MKcQCpIf0INCOvqR/iCwEArCW2h5@public.gmane.org] On
Behalf Of Jeroen Houben
> Sent: Thursday, November 17, 2005 5:23 PM
> To: rails-1W37MKcQCpIf0INCOvqR/iCwEArCW2h5@public.gmane.org
> Subject: [Rails] update_attribute send updates every field, why?
>
> Hi,
>
> If you do model.update_attribute("fname", "John") the
every field is
> updated, it generates a big update statement like:
>
> update persons set fname=x, lname=y, email=z, whatever=blah,
> and_stuff=stuff where id=1
>
> I would think it would just generate:
> update persons set fname=''John'' where id=1
>
> Anybody know why AR acts this way?
>
> Jeroen
> _______________________________________________
> Rails mailing list
> Rails-1W37MKcQCpIf0INCOvqR/iCwEArCW2h5@public.gmane.org
> http://lists.rubyonrails.org/mailman/listinfo/rails
>
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> Rails mailing list
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