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Zhao Yi

2008-Dec-26 02:00 UTC

How to get one columns as an array from database

I have a table named "Projects" which has a column "name". I
want to get
a string array to represent all the name values. In the controller, I
can use this code "@projects = Project.find(:all)" to get all the
projects but how to convert it to the string array?

thanks.
-- 
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Gabriel Laskar

2008-Dec-26 02:28 UTC

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Re: How to get one columns as an array from database

On Fri, Dec 26, 2008 at 3:00 AM, Zhao Yi
<rails-mailing-list-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org>
wrote:>
> I have a table named "Projects" which has a column
"name". I want to get
> a string array to represent all the name values. In the controller, I
> can use this code "@projects = Project.find(:all)" to get all the
> projects but how to convert it to the string array?
>
Maybe a map will do the trick

@project_names = Project.all.map { |p| p.name }


-- 
Gabriel Laskar <bibi.skuk-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>

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James Englert

2008-Dec-26 04:12 UTC

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Re: How to get one columns as an array from database

Maybe this is a bit off topic... I never knew you could use syntax like
Project.all.  When was this added to the language/framework?

On Thu, Dec 25, 2008 at 9:28 PM, Gabriel Laskar
<bibi.skuk-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
>
> On Fri, Dec 26, 2008 at 3:00 AM, Zhao Yi
> <rails-mailing-list-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org> wrote:
> >
> > I have a table named "Projects" which has a column
"name". I want to get
> > a string array to represent all the name values. In the controller, I
> > can use this code "@projects = Project.find(:all)" to get
all the
> > projects but how to convert it to the string array?
> >
>
> Maybe a map will do the trick
>
> @project_names = Project.all.map { |p| p.name }
>
>
> --
> Gabriel Laskar <bibi.skuk-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
>
> >
>
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Zhao Yi

2008-Dec-26 04:44 UTC

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Re: How to get one columns as an array from database

Gabriel Laskar wrote:> Maybe a map will do the trick
> 
> @project_names = Project.all.map { |p| p.name }
> 
> 
> --
> Gabriel Laskar <bibi.skuk-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
Thanks, it works.
-- 
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Ryan

2008-Dec-26 05:19 UTC

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Re: How to get one columns as an array from database

I think it''s been around since Rails 2.1

Project.first
Project.last
Project.all

all work.

On Dec 25, 11:12 pm, "James Englert"
<englert.ja...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:> Maybe this is a bit off topic... I never knew you could use syntax like
> Project.all.  When was this added to the language/framework?
>
> On Thu, Dec 25, 2008 at 9:28 PM, Gabriel Laskar
<bibi.s...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
>
> > On Fri, Dec 26, 2008 at 3:00 AM, Zhao Yi
> > <rails-mailing-l...-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org>
wrote:
>
> > > I have a table named "Projects" which has a column
"name". I want to get
> > > a string array to represent all the name values. In the
controller, I
> > > can use this code "@projects = Project.find(:all)" to
get all the
> > > projects but how to convert it to the string array?
>
> > Maybe a map will do the trick
>
> > @project_names = Project.all.map { |p| p.name }
>
> > --
> > Gabriel Laskar
<bibi.s...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>--~--~---------~--~----~------------~-------~--~----~
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Ryan

2008-Dec-26 05:21 UTC

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Re: How to get one columns as an array from database

A more efficient way is to do this is:

@project_names = Project.all(:select =>
''name'').map(&:name)



On Dec 25, 11:44 pm, Zhao Yi
<rails-mailing-l...-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org>
wrote:> Gabriel Laskar wrote:
> > Maybe a map will do the trick
>
> > @project_names = Project.all.map { |p| p.name }
>
> > --
> > Gabriel Laskar
<bibi.s...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
>
> Thanks, it works.
> --
> Posted viahttp://www.ruby-forum.com/.--~--~---------~--~----~------------~-------~--~----~
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Zhao Yi

2008-Dec-26 05:22 UTC

head link

Re: How to get one columns as an array from database

Ryan wrote:> I think it''s been around since Rails 2.1
> 
> Project.first
> Project.last
> Project.all
> 
> all work.
I think the first last and all refers to rows. I want to select columns.
-- 
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Zhao Yi

2008-Dec-26 05:23 UTC

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Re: How to get one columns as an array from database

Ryan wrote:> A more efficient way is to do this is:
> 
> @project_names = Project.all(:select =>
''name'').map(&:name)
Yes the map is what I am looking for.

thanks.
-- 
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Mohit Sindhwani

2008-Dec-26 05:27 UTC

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Re: How to get one columns as an array from database

Zhao Yi wrote:> Ryan wrote:
>   
>> I think it''s been around since Rails 2.1
>>
>> Project.first
>> Project.last
>> Project.all
>>
>> all work.
>>     
>
> I think the first last and all refers to rows. I want to select columns.
>   If I''m not wrong, relational algebra doesn''t identify a
sequence between
the elements of a row, i.e., I don''t think it gives you the ability to 
select a column specifically.  That said, you could probe for the schema 
and get the elements using that - something like how the dynamic 
scaffold used to work in earlier Rails.

Cheers,
Mohit.
12/26/2008 | 1:27 PM.


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Sazima

2008-Dec-26 13:23 UTC

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Re: How to get one columns as an array from database

Zhao,

I think the most straightforward way is using columns.map
(Project.columns.map { |c| puts c.name }), just like the inspect
method of ActiveRecord:

inspect()

Returns a string like ‘Post id:integer, title:string, body:text‘

 # File vendor/rails/activerecord/lib/active_record/base.rb, line 1348
1348:       def inspect
1349:         if self == Base
1350:           super
1351:         elsif abstract_class?
1352:           "#{super}(abstract)"
1353:         elsif table_exists?
1354:           attr_list = columns.map { |c| "#{c.name}: #{c.type}" }
* '', ''
1355:           "#{super}(#{attr_list})"
1356:         else
1357:           "#{super}(Table doesn''t exist)"
1358:         end
1359:       end

Cheers, Sazima

On Dec 26, 3:27 am, Mohit Sindhwani
<mo_m...-RxrYI66vbj0AvxtiuMwx3w@public.gmane.org>
wrote:> Zhao Yi wrote:
> > Ryan wrote:
>
> >> I think it''s been around since Rails 2.1
>
> >> Project.first
> >> Project.last
> >> Project.all
>
> >> all work.
>
> > I think the first last and all refers to rows. I want to select
columns.
>
> If I''m not wrong, relational algebra doesn''t identify a
sequence between
> the elements of a row, i.e., I don''t think it gives you the
ability to
> select a column specifically.  That said, you could probe for the schema
> and get the elements using that - something like how the dynamic
> scaffold used to work in earlier Rails.
>
> Cheers,
> Mohit.
> 12/26/2008 | 1:27 PM.--~--~---------~--~----~------------~-------~--~----~
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Jonzo

2008-Dec-26 22:38 UTC

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Re: How to get one columns as an array from database

On another side note:

@Ryan - You wrote:

A more efficient way is to do this is:
@project_names = Project.all(:select =>
''name'').map(&:name)

While you''ve made a database optimisation there, you''ve also
used the
shorthand notation for the map function. I read somewhere that map
(&:name) is quite a bit less efficient than map{ |p| p.name }

unfortunately I can''t find the article that convinced me in the first
place... I can only find this blog with the issue mentioned in the
comments:

http://blog.hasmanythrough.com/2006/3/7/symbol-to-proc-shorthand

On Dec 27, 2:23 am, Sazima
<rsaz...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:> Zhao,
>
> I think the most straightforward way is using columns.map
> (Project.columns.map { |c| puts c.name }), just like the inspect
> method of ActiveRecord:
>
> inspect()
>
> Returns a string like ‘Post id:integer, title:string, body:text‘
>
>  # File vendor/rails/activerecord/lib/active_record/base.rb, line 1348
> 1348:       def inspect
> 1349:         if self == Base
> 1350:           super
> 1351:         elsif abstract_class?
> 1352:           "#{super}(abstract)"
> 1353:         elsif table_exists?
> 1354:           attr_list = columns.map { |c| "#{c.name}:
#{c.type}" }
> * '', ''
> 1355:           "#{super}(#{attr_list})"
> 1356:         else
> 1357:           "#{super}(Table doesn''t exist)"
> 1358:         end
> 1359:       end
>
> Cheers, Sazima
>
> On Dec 26, 3:27 am, Mohit Sindhwani
<mo_m...-RxrYI66vbj0AvxtiuMwx3w@public.gmane.org> wrote:
>
> > Zhao Yi wrote:
> > > Ryan wrote:
>
> > >> I think it''s been around since Rails 2.1
>
> > >> Project.first
> > >> Project.last
> > >> Project.all
>
> > >> all work.
>
> > > I think the first last and all refers to rows. I want to select
columns.
>
> > If I''m not wrong, relational algebra doesn''t
identify a sequence between
> > the elements of a row, i.e., I don''t think it gives you the
ability to
> > select a column specifically.  That said, you could probe for the
schema
> > and get the elements using that - something like how the dynamic
> > scaffold used to work in earlier Rails.
>
> > Cheers,
> > Mohit.
> > 12/26/2008 | 1:27 PM.--~--~---------~--~----~------------~-------~--~----~
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Jeremy Weiskotten

2008-Dec-27 03:25 UTC

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Re: How to get one columns as an array from database

Jonathan Fantham wrote:> On another side note:
> 
> @Ryan - You wrote:
> 
> A more efficient way is to do this is:
> @project_names = Project.all(:select =>
''name'').map(&:name)
> 
> While you''ve made a database optimisation there, you''ve
also used the
> shorthand notation for the map function. I read somewhere that map
> (&:name) is quite a bit less efficient than map{ |p| p.name }
> 
> unfortunately I can''t find the article that convinced me in the
first
> place... I can only find this blog with the issue mentioned in the
> comments:
> 
> http://blog.hasmanythrough.com/2006/3/7/symbol-to-proc-shorthand
The Symbol#to_proc syntax is slower than a block, but unless you''re 
doing it thousands of times, the single trip to the database is probably 
at least a few orders of magnitude more expensive.
-- 
Posted via http://www.ruby-forum.com/.

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Ryan

2008-Dec-28 18:06 UTC

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Re: How to get one columns as an array from database

Cool.  Learn something new all the time.

Thanks.

On Dec 26, 5:38 pm, Jonzo
<j.fant...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:> On another side note:
>
> @Ryan - You wrote:
>
> A more efficient way is to do this is:
> @project_names = Project.all(:select =>
''name'').map(&:name)
>
> While you''ve made a database optimisation there, you''ve
also used the
> shorthand notation for the map function. I read somewhere that map
> (&:name) is quite a bit less efficient than map{ |p| p.name }
>
> unfortunately I can''t find the article that convinced me in the
first
> place... I can only find this blog with the issue mentioned in the
> comments:
>
> http://blog.hasmanythrough.com/2006/3/7/symbol-to-proc-shorthand
>
> On Dec 27, 2:23 am, Sazima
<rsaz...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
>
> > Zhao,
>
> > I think the most straightforward way is using columns.map
> > (Project.columns.map { |c| puts c.name }), just like the inspect
> > method of ActiveRecord:
>
> > inspect()
>
> > Returns a string like ‘Post id:integer, title:string, body:text‘
>
> >  # File vendor/rails/activerecord/lib/active_record/base.rb, line 1348
> > 1348:       def inspect
> > 1349:         if self == Base
> > 1350:           super
> > 1351:         elsif abstract_class?
> > 1352:           "#{super}(abstract)"
> > 1353:         elsif table_exists?
> > 1354:           attr_list = columns.map { |c| "#{c.name}:
#{c.type}" }
> > * '', ''
> > 1355:           "#{super}(#{attr_list})"
> > 1356:         else
> > 1357:           "#{super}(Table doesn''t exist)"
> > 1358:         end
> > 1359:       end
>
> > Cheers, Sazima
>
> > On Dec 26, 3:27 am, Mohit Sindhwani
<mo_m...-RxrYI66vbj0AvxtiuMwx3w@public.gmane.org> wrote:
>
> > > Zhao Yi wrote:
> > > > Ryan wrote:
>
> > > >> I think it''s been around since Rails 2.1
>
> > > >> Project.first
> > > >> Project.last
> > > >> Project.all
>
> > > >> all work.
>
> > > > I think the first last and all refers to rows. I want to
select columns.
>
> > > If I''m not wrong, relational algebra doesn''t
identify a sequence between
> > > the elements of a row, i.e., I don''t think it gives you
the ability to
> > > select a column specifically.  That said, you could probe for the
schema
> > > and get the elements using that - something like how the dynamic
> > > scaffold used to work in earlier Rails.
>
> > > Cheers,
> > > Mohit.
> > > 12/26/2008 | 1:27 PM.--~--~---------~--~----~------------~-------~--~----~
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Rails - Dec 2008 - How to get one columns as an array from database

How to get one columns as an array from database

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