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Ankur Jain

2012-Apr-19 21:03 UTC

Trivial Rails Question, I am unable to explain the behavior

Following 2 statements look identical to me, however the first one returns
only one object but the second one returns correctly an array of 4 objects.

What is happening here is simple, I get all the Grade objects (1st one
using Grade.find(:all) and second one using Grade.all), and then filter out
all the grade objects where they have worksheets assigned to them.


*
*
*@grades = Grade.find(:all){|grade| Worksheet.find(:all,:conditions=>
[''grade_id =?'',grade.id]).count > 0}*
*
*
*@grades = Grade.all        {|grade| Worksheet.find(:all,:conditions=>
[''grade_id =?'',grade.id]).count > 0}*

Can somebody explain why the results would be different for these 2
statements.

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Tyler

2012-Apr-20 02:08 UTC

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Re: Trivial Rails Question, I am unable to explain the behavior

I don''t have rails in front of me, but looks like there may be a
problem
with implied parentheses.  Have you tried things like:
*@grades = Grade.all()       {|grade| Worksheet.find(:all,:conditions=> 
[''grade_id =?'',grade.id]).count > 0}* *
*

Again I can''t test so not sure if that helps


On Thursday, April 19, 2012 2:03:05 PM UTC-7, Ankur Jain
wrote:>
> Following 2 statements look identical to me, however the first one returns 
> only one object but the second one returns correctly an array of 4 objects.
>
> What is happening here is simple, I get all the Grade objects (1st one 
> using Grade.find(:all) and second one using Grade.all), and then filter out
> all the grade objects where they have worksheets assigned to them.
>
>
> *
> *
> *@grades = Grade.find(:all){|grade| Worksheet.find(:all,:conditions=> 
> [''grade_id =?'',grade.id]).count > 0}*
> *
> *
> *@grades = Grade.all        {|grade| Worksheet.find(:all,:conditions=> 
> [''grade_id =?'',grade.id]).count > 0}*
>
> Can somebody explain why the results would be different for these 2 
> statements.
>
>
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Dheeraj Kumar

2012-Apr-20 02:14 UTC

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Re: Trivial Rails Question, I am unable to explain the behavior

The find method takes the option hash as the last parameter. Either use
Model.all(options) or Model.find(:all, options)

The correct code is:

@grades = Grade.find(:all, {|grade| Worksheet.find(:all,:conditions=>
[''grade_id =?'',grade.id (http://grade.id)]).count > 0})




Dheeraj Kumar


On Friday 20 April 2012 at 7:38 AM, Tyler wrote:
> I don''t have rails in front of me, but looks like there may be a
problem with implied parentheses.  Have you tried things like:
> @grades = Grade.all()       {|grade| Worksheet.find(:all,:conditions=>
[''grade_id =?'',grade.id (http://grade.id/)]).count > 0}
> 
> Again I can''t test so not sure if that helps
> 
> 
> On Thursday, April 19, 2012 2:03:05 PM UTC-7, Ankur Jain wrote:
> > Following 2 statements look identical to me, however the first one
returns only one object but the second one returns correctly an array of 4
objects.
> > 
> > What is happening here is simple, I get all the Grade objects (1st one
using Grade.find(:all) and second one using Grade.all), and then filter out all
the grade objects where they have worksheets assigned to them.
> > 
> > 
> > 
> > @grades = Grade.find(:all){|grade|
Worksheet.find(:all,:conditions=> [''grade_id =?'',grade.id
(http://grade.id)]).count > 0}
> > 
> > @grades = Grade.all        {|grade|
Worksheet.find(:all,:conditions=> [''grade_id =?'',grade.id
(http://grade.id)]).count > 0}
> > 
> > Can somebody explain why the results would be different for these 2
statements.
> > 
> -- 
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Matt Jones

2012-Apr-20 14:22 UTC

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Re: Trivial Rails Question, I am unable to explain the behavior

On Thursday, 19 April 2012 22:14:51 UTC-4, Dheeraj Kumar
wrote:>
> The find method takes the option hash as the last parameter. Either use 
> Model.all(options) or Model.find(:all, options)
>
> The correct code is:
> *
> *
> *@grades = Grade.find(:all, {|grade| Worksheet.find(:all,:conditions=> 
> [''grade_id =?'',*grade.id*]).count > 0})*
> *
> *
> *
> *
>
Um, no. That won''t even parse.
 
 
> On Friday 20 April 2012 at 7:38 AM, Tyler wrote:
>
> I don''t have rails in front of me, but looks like there may be a
problem
> with implied parentheses.  Have you tried things like:
> *@grades = Grade.all()       {|grade| Worksheet.find(:all,:conditions=> 
> [''grade_id =?'',grade.id]).count > 0}* *
> *
>
> Again I can''t test so not sure if that helps
>
>
> On Thursday, April 19, 2012 2:03:05 PM UTC-7, Ankur Jain wrote:
>
> Following 2 statements look identical to me, however the first one returns 
> only one object but the second one returns correctly an array of 4 objects.
>
> What is happening here is simple, I get all the Grade objects (1st one 
> using Grade.find(:all) and second one using Grade.all), and then filter out
> all the grade objects where they have worksheets assigned to them.
>
>
> *
> *
> *@grades = Grade.find(:all){|grade| Worksheet.find(:all,:conditions=> 
> [''grade_id =?'',grade.id]).count > 0}*
> *
> *
> *@grades = Grade.all        {|grade| Worksheet.find(:all,:conditions=> 
> [''grade_id =?'',grade.id]).count > 0}*
>
>There are two things going on here: 

- in the first statement, find(:all) acts like Enumerable#find when passed 
a block. Each of the found objects is passed to the block and the first one 
that returns a truthy value is returned.

- in the second statement, all doesn''t call the block so you get
exactly
the same results you would have without a block at all.

If this is an operation you do a lot in your app, you may want to check out 
the :counter_cache option of belongs_to, which will allow you to write this 
(correctly) as:

@grades = Grade.where(''worksheets_count > 0'').all

Also note that if counts are all you''re looking for, you should avoid
doing
a find(:all) on them (as on Worksheet above); the count method on the model 
class can do this much more efficiently (with a SQL COUNT statement, rather 
than loading a bunch of objects and then counting them).

--Matt Jones

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Ankur Jain

2012-Apr-20 14:54 UTC

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Re: Re: Trivial Rails Question, I am unable to explain the behavior

Thanks Matt, Your alternative method on how to best get the data definitely
is a much optimized solution then what I was using, I am not using that and
everything works great.

However, I am still confused on one part.

as per my understanding

*Grade.find(:all)*

and

*Grade.all *

both should return an array of Grade objects, so how are the results
different if I just pass the objects through this block.
{|grade| Worksheet.find(:all,:conditions=> [''grade_id
=?'',grade.id]).count> 0}
Thanks again for the help.

On Fri, Apr 20, 2012 at 10:22 AM, Matt Jones
<al2o3cr-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
>
>
> On Thursday, 19 April 2012 22:14:51 UTC-4, Dheeraj Kumar wrote:
>>
>> The find method takes the option hash as the last parameter. Either use
>> Model.all(options) or Model.find(:all, options)
>>
>> The correct code is:
>> *
>> *
>> *@grades = Grade.find(:all, {|grade|
Worksheet.find(:all,:conditions=>
>> [''grade_id =?'',*grade.id*]).count > 0})*
>> *
>> *
>> *
>> *
>>
>
> Um, no. That won''t even parse.
>
>
>
>> On Friday 20 April 2012 at 7:38 AM, Tyler wrote:
>>
>> I don''t have rails in front of me, but looks like there may be
a problem
>> with implied parentheses.  Have you tried things like:
>> *@grades = Grade.all()       {|grade|
Worksheet.find(:all,:conditions=>
>> [''grade_id =?'',grade.id]).count > 0}* *
>> *
>>
>> Again I can''t test so not sure if that helps
>>
>>
>> On Thursday, April 19, 2012 2:03:05 PM UTC-7, Ankur Jain wrote:
>>
>> Following 2 statements look identical to me, however the first one
>> returns only one object but the second one returns correctly an array
of 4
>> objects.
>>
>> What is happening here is simple, I get all the Grade objects (1st one
>> using Grade.find(:all) and second one using Grade.all), and then filter
out
>> all the grade objects where they have worksheets assigned to them.
>>
>>
>> *
>> *
>> *@grades = Grade.find(:all){|grade|
Worksheet.find(:all,:conditions=>
>> [''grade_id =?'',grade.id]).count > 0}*
>> *
>> *
>> *@grades = Grade.all        {|grade|
Worksheet.find(:all,:conditions=>
>> [''grade_id =?'',grade.id]).count > 0}*
>>
>>
> There are two things going on here:
>
> - in the first statement, find(:all) acts like Enumerable#find when passed
> a block. Each of the found objects is passed to the block and the first one
> that returns a truthy value is returned.
>
> - in the second statement, all doesn''t call the block so you get
exactly
> the same results you would have without a block at all.
>
> If this is an operation you do a lot in your app, you may want to check
> out the :counter_cache option of belongs_to, which will allow you to write
> this (correctly) as:
>
> @grades = Grade.where(''worksheets_count > 0'').all
>
> Also note that if counts are all you''re looking for, you should
avoid
> doing a find(:all) on them (as on Worksheet above); the count method on the
> model class can do this much more efficiently (with a SQL COUNT statement,
> rather than loading a bunch of objects and then counting them).
>
> --Matt Jones
>
>  --
> You received this message because you are subscribed to the Google Groups
> "Ruby on Rails: Talk" group.
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> https://groups.google.com/d/msg/rubyonrails-talk/-/gr_Z8phcivsJ.
>
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>
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Matt Jones

2012-Apr-21 14:30 UTC

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Re: Re: Trivial Rails Question, I am unable to explain the behavior

On Friday, 20 April 2012 10:54:13 UTC-4, Ankur Jain
wrote:>
>
> Thanks Matt, Your alternative method on how to best get the 
> data definitely is a much optimized solution then what I was using, I am 
> not using that and everything works great.
>
> However, I am still confused on one part.
>
> as per my understanding
>
> *Grade.find(:all)*
>
> and 
>
> *Grade.all *
>
> both should return an array of Grade objects, so how are the results 
> different if I just pass the objects through this block.
> {|grade| Worksheet.find(:all,:conditions=> [''grade_id
=?'',grade.id]).count
> > 0}
>
>A block by itself doesn''t do ANYTHING - it''s entirely
dependent on the
function it''s passed to. For instance:

def hello(who)
  puts "Hello #{who}"
end

hello(''World'') # prints "Hello World"
hello(''World'') { |x| puts ''WAT'' } # prints
"Hello World" - doesn''t do
anything with the block

The case you encountered with find(:all) was specifically coded to use the 
block just like Enumerable#find:

a = [1,2,3,4]

a.find { |x| x > 2 } # => returns 3, the first value in the array that the
block returns a truthy value for

--Matt Jones


 

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Rails - Apr 2012 - Trivial Rails Question, I am unable to explain the behavior

Trivial Rails Question, I am unable to explain the behavior

Re: Trivial Rails Question, I am unable to explain the behavior

Re: Trivial Rails Question, I am unable to explain the behavior

Re: Trivial Rails Question, I am unable to explain the behavior

Re: Re: Trivial Rails Question, I am unable to explain the behavior

Re: Re: Trivial Rails Question, I am unable to explain the behavior