Rails - Apr 2010 - Find distinct values in an array of database results

My problem is similar to http://www.ruby-forum.com/topic/171399, but I
don''t understand how the asker solved the problem.

I have a model called issues. It returns results that contain a field
called "status". The results might look like this:

open
open
closed
in progress
open
open

How can I use the "uniq" method on the model in order to return a
unique
list of statuses like this:

open
closed
in progress
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In addition to my question above, I''d also like to apply the equivalent
of a ''where'' clause without forcing another SQL query, in
order to get
all the columns for "issues" where "status=open". The
results would be:

1, open, fred
2, open, john
5, open, john
6, open, sara
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On Wed, Apr 14, 2010 at 11:14 PM, joe mejoe
<lists-fsXkhYbjdPsEEoCn2XhGlw@public.gmane.org>
wrote:
> In addition to my question above, I''d also like to apply the
equivalent
> of a ''where'' clause without forcing another SQL query, in
order to get
# modify this as needed
results = Issue.find(...)

statuses = results.collect(&:status).uniq.sort

open_issues = results.collect { |i| i.status == ''open'' }

I suggest you read up on the Array class and its methods
collect, uniq and sort which I used here.

Have fun.

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If I may jump in, I''m interested in understanding why you would do this
kind of database job with Ruby vs. an extra SQL query.
I had the feeling that it would be wiser (and would execute faster) to delegate
the job to the database engine

But I''m kind of amateur.

Thanks to anyone who is willing to put some light for me
 
Christophe

Le 15 avr. 2010 à 10:01, Franz Strebel a écrit :
> On Wed, Apr 14, 2010 at 11:14 PM, joe mejoe
<lists-fsXkhYbjdPsEEoCn2XhGlw@public.gmane.org> wrote:
>> In addition to my question above, I''d also like to apply the
equivalent
>> of a ''where'' clause without forcing another SQL
query, in order to get
> 
> # modify this as needed
> results = Issue.find(...)
> 
> statuses = results.collect(&:status).uniq.sort
> 
> open_issues = results.collect { |i| i.status == ''open'' }
> 
> I suggest you read up on the Array class and its methods
> collect, uniq and sort which I used here.
> 
> Have fun.
> 
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Christophe Decaux wrote:
> If I may jump in, I''m interested in understanding why you would do
this
> kind of database job with Ruby vs. an extra SQL query.
> I had the feeling that it would be wiser (and would execute faster) to 
> delegate the job to the database engine
I agree. This is a job for SELECT DISTINCT, unless you''ve already got 
the recordset stored from a previous operation.

In general, do your DB queries on the DB side.
> 
> But I''m kind of amateur.
> 
> Thanks to anyone who is willing to put some light for me
Light: many Rails developers don''t know how to use a DB properly. :)
> 
> Christophe
> 
> Le 15 avr. 2010 � 10:01, Franz Strebel a �crit :
Best,
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http://www.marnen.org
marnen-sbuyVjPbboAdnm+yROfE0A@public.gmane.org
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Sometimes you''re not querying a database (for example a REST service
that returns a json result). Specially in web applications.

On Apr 15, 12:15 pm, Marnen Laibow-Koser
<li...-fsXkhYbjdPsEEoCn2XhGlw@public.gmane.org>
wrote:
> Christophe Decaux wrote:
> > If I may jump in, I''m interested in understanding why you
would do this
> > kind of database job with Ruby vs. an extra SQL query.
> > I had the feeling that it would be wiser (and would execute faster) to
> > delegate the job to the database engine
>
> I agree. This is a job for SELECT DISTINCT, unless you''ve already
got
> the recordset stored from a previous operation.
>
> In general, do your DB queries on the DB side.
>
>
>
> > But I''m kind of amateur.
>
> > Thanks to anyone who is willing to put some light for me
>
> Light: many Rails developers don''t know how to use a DB properly.
:)
>
>
>
> > Christophe
>
> > Le 15 avr. 2010 10:01, Franz Strebel a crit :
>
> Best,
> --
> Marnen Laibow-Koserhttp://www.marnen.org
> mar...-sbuyVjPbboAdnm+yROfE0A@public.gmane.org
> --
> Posted viahttp://www.ruby-forum.com/.
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[Please quote when replying, so we know what in particular you''re 
responding to.]

Vincent M. wrote:
> Sometimes you''re not querying a database (for example a REST
service
> that returns a json result). Specially in web applications.
True.  But where you have a database, you should use it. :)

Especially in Web applications?  I don''t know.  I think I''ve
used more
non-Web apps that query Web services than Web apps that do likewise.

Best,
--
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http://www.marnen.org
marnen-sbuyVjPbboAdnm+yROfE0A@public.gmane.org
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On Mon, Apr 26, 2010 at 10:42 PM, Marnen Laibow-Koser
<lists-fsXkhYbjdPsEEoCn2XhGlw@public.gmane.org>
wrote:
> [Please quote when replying, so we know what in particular you''re
> responding to.]
>
> Vincent M. wrote:
>> Sometimes you''re not querying a database (for example a REST
service
>> that returns a json result). Specially in web applications.
>
> True.  But where you have a database, you should use it. :)
Sure, however, the original poster specifically wanted to avoid querying the
database twice, which is why the solution ended up Ruby side.

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Franz Strebel wrote:
> On Mon, Apr 26, 2010 at 10:42 PM, Marnen Laibow-Koser
> <lists-fsXkhYbjdPsEEoCn2XhGlw@public.gmane.org> wrote:
>> [Please quote when replying, so we know what in particular
you''re
>> responding to.]
>>
>> Vincent M. wrote:
>>> Sometimes you''re not querying a database (for example a
REST service
>>> that returns a json result). Specially in web applications.
>>
>> True. �But where you have a database, you should use it. :)
> 
> Sure, however, the original poster specifically wanted to avoid querying 
> the
> database twice, which is why the solution ended up Ruby side.
As far as I can tell, the OP asked two unrelated questions.  I only 
answered one of them.

Best,
--
Marnen Laibow-Koser
http://www.marnen.org
marnen-sbuyVjPbboAdnm+yROfE0A@public.gmane.org
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