Rails - Jun 2011 - instantiating object and passing a new array into the block

Hey all,

Out of curiousity, all in Rails grabs all the records and converts
them into an array. Map then iterates through the returned array,
returning a new array. So why even use map here? And then the array
gets passed as local variable bt. And we instantiate object and assign
the bt array as a value of a hash of book_type. I dont see why map is
needed here.


book_details = BookType.all.map do |bt|
  Student.new(:book_type => bt)
end

Thanks for response.

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On Jun 24, 2011, at 2:42 PM, John Merlino wrote:
> Hey all,
>
> Out of curiousity, all in Rails grabs all the records and converts
> them into an array. Map then iterates through the returned array,
> returning a new array. So why even use map here? And then the array
> gets passed as local variable bt. And we instantiate object and assign
> the bt array as a value of a hash of book_type. I dont see why map is
> needed here.
>
>
> book_details = BookType.all.map do |bt|
>  Student.new(:book_type => bt)
> end
>
> Thanks for response.
In Rails 3, a lot of the query stuff is lazy-loaded, so you may not  
actually be getting the query you think here. Try it out in rails  
console, or just look at your development log to see the actual SQL  
that''s being generated. Arel waits until the last possible second  
before actually issuing a query, so it may be digging out only the  
records you need, rather than getting all of them and winnowing down.

Walter


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On Jun 24, 7:42 pm, John Merlino <stoici...-YDxpq3io04c@public.gmane.org>
wrote:
> Hey all,
>
> Out of curiousity, all in Rails grabs all the records and converts
> them into an array. Map then iterates through the returned array,
> returning a new array. So why even use map here? And then the array
> gets passed as local variable bt. And we instantiate object and assign
> the bt array as a value of a hash of book_type. I dont see why map is
> needed here.
>
> book_details = BookType.all.map do |bt|
>   Student.new(:book_type => bt)
> end
So what do you think this could be simplified to if the use of map is
omitted?

Fred
>
> Thanks for response.
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