Rails - Apr 2007 - best way to check if record exists? count with limit 1?

I have a check between friends that is happening on each listing.

Right now I do

@c.friends.find(:first, :conditions=> ["id=?",users])

This seems kind of overkill.


For something like this, would you guys recommend:

@c.friends.count(:first, options={})

Is that the least db intensive way of doing it?

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Woops I mean count(:limit=>1)

Aryk Grosz wrote:
> I have a check between friends that is happening on each listing.
> 
> Right now I do
> 
> @c.friends.find(:first, :conditions=> ["id=?",users])
> 
> This seems kind of overkill.
> 
> 
> For something like this, would you guys recommend:
> 
> @c.friends.count(:first, options={})
> 
> Is that the least db intensive way of doing it?

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or should i just use count without the Limit 1

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On Apr 15, 2007, at 10:56 PM, Aryk Grosz wrote:
> or should i just use count without the Limit 1
Why not:

   begin
     find
   rescue
     # doesn''t exist
   end

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On 4/15/07, Aryk Grosz
<rails-mailing-list-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org>
wrote:
>
> I have a check between friends that is happening on each listing.
>
> Right now I do
>
> @c.friends.find(:first, :conditions=> ["id=?",users])
>
> This seems kind of overkill.
>
>
> For something like this, would you guys recommend:
>
> @c.friends.count(:first, options={})
>
> Is that the least db intensive way of doing it?
@c.friends.find_by_id params[:friend_id]

that will return nil if the user doesn''t exist.

If you don''t need to load the friend object into memory, sure, you
could do a count instead of a find.

There''s really nothing intensive about this, assuming you have indexes
setup.  Considering that one user should probably only be able to be
friends with another user once, you can create a unique index, which
will be very zippy.

Also, be on the lookout for signs that you might want to promote a
Friendship to its own abstraction.

Pat

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The thing is that I''m not looking up the record on its ID column, im 
looking it up on a combination of attributes.

Nevertheless, If I use find first, it will return the object into 
memory. If I use count, than it will count all the occurences.

Isn''t the best way to just test if it exists to do a count with a limit
1?

Wouldn''t that be the least database intensive. Is there a functon right
now to do this besides having to do Model.count(:limit=>1, 
:conditions=>"user_id=4 and book_id=7") > 0 ?


OR Am I just plain being to picky and should just use find :first?

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Hi Aryk,

Aryk Grosz wrote:

> Isn''t the best way to just test if it exists to do a count with
> a limit 1?
The best way would probably be to use the exists? method.  I''m not sure
of
the exact syntax, but for a start you might try...

answer = Model.exists?(["user_id = ? and  book_id = ?", 4, 7])

hth,
Bill




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Bill,

If you look at the code for the "exists?" function, you''ll
see that its
really just another way of writing find :first.

Which leads me to ask:

Why not just use count with limit 1 instead of find with limit 1?

I just don''t get it. It is no extra code to achieve the same results 
faster. What am I missing here?

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On 4/16/07, Aryk Grosz
<rails-mailing-list-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org>
wrote:
>
> Bill,
>
> If you look at the code for the "exists?" function,
you''ll see that its
> really just another way of writing find :first.
That''s the difference between interface and implementation.  You can
look at exists? and know what it does without caring how it does it.

> Which leads me to ask:
>
> Why not just use count with limit 1 instead of find with limit 1?
>
> I just don''t get it. It is no extra code to achieve the same
results
> faster. What am I missing here?
Nothing.  You''re just looking way too much into this.  Go ahead and
use count if you really want to.  Heck, you can even override
AR::Base.exists? to use a count implementation instead of find, if
that''s what you want.

Pat

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Hey pat, I think I might just do that. Thanks for the response. =)


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