Rails - Dec 2008 - Get a collection using an array of ids, keeping the order

Say if i have an array of resource ids, of size n.  Is there a way to
get all the corresponding resources, without doing n individual Find
calls?

eg, i could do this:

@resources = []
array.each{|id| @resources << Resource.find(id)}

But, this requires n Find calls which isn''t acceptable.

Any ideas anyone?

thanks
max
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On 4 Dec 2008, at 12:24, Max Williams wrote:
>
> Say if i have an array of resource ids, of size n.  Is there a way to
> get all the corresponding resources, without doing n individual Find
> calls?
>
> eg, i could do this:
>
> @resources = []
> array.each{|id| @resources << Resource.find(id)}
>
> But, this requires n Find calls which isn''t acceptable.
Resource.find @resources

Fred
>
>
> Any ideas anyone?
>
> thanks
> max
> --  
> Posted via http://www.ruby-forum.com/.
>
> >

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On 4 Dec 2008, at 12:31, Frederick Cheung wrote:
>
> On 4 Dec 2008, at 12:24, Max Williams wrote:
>
>>
>> Say if i have an array of resource ids, of size n.  Is there a way to
>> get all the corresponding resources, without doing n individual Find
>> calls?
>>
>> eg, i could do this:
>>
>> @resources = []
>> array.each{|id| @resources << Resource.find(id)}
>>
>> But, this requires n Find calls which isn''t acceptable.
>
> Resource.find @resources
>
Sorry, only read the body of the message, not the subject!
I would sort it after, eg

order_hash = {}
array.each_with_index {|id, index| order_hash[id]=index
Resource.find(array).sort_by {|r| order_hash[r.id]}

Fred

> Fred
>>
>>
>> Any ideas anyone?
>>
>> thanks
>> max
>> -- Posted via http://www.ruby-forum.com/.
>>
>> >>
>

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Frederick Cheung wrote:
> On 4 Dec 2008, at 12:31, Frederick Cheung wrote:
> 
>>> @resources = []
>>> array.each{|id| @resources << Resource.find(id)}
>>>
>>> But, this requires n Find calls which isn''t acceptable.
>>
>> Resource.find @resources
>>
> Sorry, only read the body of the message, not the subject!
> I would sort it after, eg
> 
> order_hash = {}
> array.each_with_index {|id, index| order_hash[id]=index
> Resource.find(array).sort_by {|r| order_hash[r.id]}
> 
> Fred
ah yes, of course.  Nice touch with the hash (as opposed to sorting by 
array.index) :)

Thanks a lot, Fred.

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On Dec 4, 2008, at 7:46 AM, Max Williams wrote:
> Frederick Cheung wrote:
>> On 4 Dec 2008, at 12:31, Frederick Cheung wrote:
>>
>>>> @resources = []
>>>> array.each{|id| @resources << Resource.find(id)}
>>>>
>>>> But, this requires n Find calls which isn''t
acceptable.
>>>
>>> Resource.find @resources
>>>
>> Sorry, only read the body of the message, not the subject!
>> I would sort it after, eg
>>
>> order_hash = {}
>> array.each_with_index {|id, index| order_hash[id]=index
>> Resource.find(array).sort_by {|r| order_hash[r.id]}
>>
>> Fred
>
> ah yes, of course.  Nice touch with the hash (as opposed to sorting by
> array.index) :)
>
> Thanks a lot, Fred.

YMMV, but why bother with the hash?  Unless you have a truly huge list  
of id''s

@resources = Resource.find(array).sort_by {|r| array.index(r.id)}

You could even hide the implementation:

class Resource
   def self.find_by_ordered_ids(*array)
     options = {}
     options = array.pop if array.last.is_a? Hash
     # pass an Array or a list of id arguments
     array = array.flatten if array.first.is_a? Array
     find(array, options).sort_by {|r| array.index(r.id)}
   end
end

(Note, untested, but that doesn''t mean that it *won''t* work
;-)

-Rob

Rob Biedenharn		http://agileconsultingllc.com
Rob-xa9cJyRlE0mWcWVYNo9pwxS2lgjeYSpx@public.gmane.org

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If you use MySQL, the "field" function allows you
to retrieve records in a specific id order:

http://groups.google.com/group/rubyonrails-talk/browse_thread/thread/158dc2d879b2fb1/af78ce75ddfa1ed1

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Mark Reginald James wrote:
> If you use MySQL, the "field" function allows you
> to retrieve records in a specific id order:
> 
>
http://groups.google.com/group/rubyonrails-talk/browse_thread/thread/158dc2d879b2fb1/af78ce75ddfa1ed1
> 
> --
> Rails Wheels - Find Plugins, List & Sell Plugins - 
> http://railswheels.com
Ah, now that is a great tip, i''d not seen this before!  Thanks a lot.

The weird thing is, i''ve gone to my console to try it out, and rails is
now always giving me the resources back in the order of the id array 
anyway, whether i use the field option or not.  It''s the same with any 
of my AR classes!  I''m sure that this didn''t used to happen
though...i
think i''m going crazy.  Can anyone tell me if this is normal?  If so 
then i just imagined this whole problem...

AModel.find([3,1,2]).collect(&:id)
=> [3,1,2]

or do you get

=> [1,2,3]

?
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Max Williams wrote:
> The weird thing is, i''ve gone to my console to try it out, and
rails is
> now always giving me the resources back in the order of the id array 
> anyway, whether i use the field option or not.  It''s the same with
any
> of my AR classes!  I''m sure that this didn''t used to
happen though...i
> think i''m going crazy.  Can anyone tell me if this is normal?
You are not going crazy.

MySQL may, but is not required to, return the objects in the order of 
the array.  So, the behavior will change without warning.

You still need to sort after the fetch.
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On 23 August 2010 03:18, Robert Head
<lists-fsXkhYbjdPsEEoCn2XhGlw@public.gmane.org>
wrote:
> Max Williams wrote:
>> i think i''m going crazy.  Can anyone tell me if this is
normal?
>
> You are not going crazy.
I am! This is a reply to a two-year-old thread... I just wasted 10
minutes trying to find out why I hadn''t received the previous
messages. I thought my email spam filter was being paranoid :-/

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