Rails - Apr 2006 - How should I pick a random entry from the database?

Hi guys. Total newbie here. I''ve been doing web stuff since 1996 but 
only began the foray into scripting last year. I haven''t got my skull 
completely 360 degrees around OOP yet. It''s just me here (in Japan) and
there are no Ruby groups in my area (never mind any in English).

I''ve got a database table - real simple: question, answer, and id
fields
- and I want to pick one question out randomly and output to the HTML 
page. Right now I can''t even get single entries out - all I can do is 
copy and paste from the scaffolding, so it''s every question or no 
questions at this point. I''m not sure if you can put the value into a 
variable, like ''@question'', and then print that, or if i have
to do
something like make @question into an intermediary object, like 
''question'', and then do something like
''question.question'' to make it
print out. Actually, if somebody could just tell me that, even if you 
don''t know how to do the random thing, it would be appreciated.

Thanks!

-- 
Posted via http://www.ruby-forum.com/.

sean colquhoun wrote:
> Hi guys. Total newbie here. I''ve been doing web stuff since 1996
but
> only began the foray into scripting last year. I haven''t got my
skull
> completely 360 degrees around OOP yet. It''s just me here (in
Japan) and
> there are no Ruby groups in my area (never mind any in English).
> 
> I''ve got a database table - real simple: question, answer, and id
fields
> - and I want to pick one question out randomly and output to the HTML 
> page. Right now I can''t even get single entries out - all I can do
is
> copy and paste from the scaffolding, so it''s every question or no 
> questions at this point. I''m not sure if you can put the value
into a
> variable, like ''@question'', and then print that, or if i
have to do
> something like make @question into an intermediary object, like 
> ''question'', and then do something like
''question.question'' to make it
> print out. Actually, if somebody could just tell me that, even if you 
> don''t know how to do the random thing, it would be appreciated.
> 
> Thanks!
Hi,

To select a specific row you use Model.find(id), where model stands for 
the class that represents your question-answer table. So you could try 
this out by something like
@entry = YourModel.find(id_you_know_that_exists)
and in the view display the question like <%= @entry.question %>

To pick a random question you could try first retrieving all entries 
from that table, then picking a random one from them, like
entries = YourModel.find(:all)
@entry = entries[rand(entries.size-1)]

However, if this table is going to be huge this approach would be very 
inefficient, just giving you a hint for the easiest way to start with it 
:)

--
Agnieszka

-- 
Posted via http://www.ruby-forum.com/.

> However, if this table is going to be huge this approach would be very
> inefficient, just giving you a hint for the easiest way to start with it
So what would be the Rails Way of doing this for a huge table? 
Storing the number
of available records in another table, or somewhere else?

--
----------------------------------------------------
http://sobrerailes.com

I''m partial to the SQL approach:

 object.find(:all, :order => "Rand()")


On 4/3/06, Juan Lupi?n <pantulis@gmail.com> wrote:
> > However, if this table is going to be huge this approach would be very
> > inefficient, just giving you a hint for the easiest way to start with
it
>
> So what would be the Rails Way of doing this for a huge table?
> Storing the number
> of available records in another table, or somewhere else?
>
> --
> ----------------------------------------------------
> http://sobrerailes.com
> _______________________________________________
> Rails mailing list
> Rails@lists.rubyonrails.org
> http://lists.rubyonrails.org/mailman/listinfo/rails
>

size = Model.count

obj= Model.find(rand(size+))

Assuming the ID''s are sequential...

On Monday, April 03, 2006, at 12:29 PM, Agnieszka Figiel
wrote:
>sean colquhoun wrote:
>> Hi guys. Total newbie here. I''ve been doing web stuff since
1996 but
>> only began the foray into scripting last year. I haven''t got
my skull
>> completely 360 degrees around OOP yet. It''s just me here (in
Japan) and
>> there are no Ruby groups in my area (never mind any in English).
>>
>> I''ve got a database table - real simple: question, answer, and
id fields
>> - and I want to pick one question out randomly and output to the HTML
>> page. Right now I can''t even get single entries out - all I
can do is
>> copy and paste from the scaffolding, so it''s every question or
no
>> questions at this point. I''m not sure if you can put the value
into a
>> variable, like ''@question'', and then print that, or
if i have to do
>> something like make @question into an intermediary object, like
>> ''question'', and then do something like
''question.question'' to make it
>> print out. Actually, if somebody could just tell me that, even if you
>> don''t know how to do the random thing, it would be
appreciated.
>>
>> Thanks!
>
>Hi,
>
>To select a specific row you use Model.find(id), where model stands for
>the class that represents your question-answer table. So you could try
>this out by something like
>@entry = YourModel.find(id_you_know_that_exists)
>and in the view display the question like <%= @entry.question %>
>
>To pick a random question you could try first retrieving all entries
>from that table, then picking a random one from them, like
>entries = YourModel.find(:all)
>@entry = entries[rand(entries.size-1)]
>
>However, if this table is going to be huge this approach would be very
>inefficient, just giving you a hint for the easiest way to start with it
>:)
>
>--
>Agnieszka
>
>--
>Posted via http://www.ruby-forum.com/.
>_______________________________________________
>Rails mailing list
>Rails@lists.rubyonrails.org
>http://lists.rubyonrails.org/mailman/listinfo/rails

Mikkel Bruun

www.strongside.dk    - Football Portal(DK)
ting.minline.dk      - Buy Old Stuff!(DK)



-- 
Posted with http://DevLists.com.  Sign up and save your mailbox.

Mikkel Bruun wrote:
> 
> size = Model.count
> obj= Model.find(rand(size+))
> 
> Assuming the ID''s are sequential...
Yeah... if rows get deleted, the IDs won''t be reused so there will be
gaps. This seems
problematic. Sucks to pull all rows, but Tim''s approach might be
safest.

b
> On Monday, April 03, 2006, at 12:29 PM, Agnieszka Figiel wrote:
> 
>>sean colquhoun wrote:
>>
>>>Hi guys. Total newbie here. I''ve been doing web stuff since
1996 but
>>>only began the foray into scripting last year. I haven''t
got my skull
>>>completely 360 degrees around OOP yet. It''s just me here
(in Japan) and
>>>there are no Ruby groups in my area (never mind any in English).
>>>
>>>I''ve got a database table - real simple: question, answer,
and id fields
>>>- and I want to pick one question out randomly and output to the
HTML
>>>page. Right now I can''t even get single entries out - all I
can do is
>>>copy and paste from the scaffolding, so it''s every question
or no
>>>questions at this point. I''m not sure if you can put the
value into a
>>>variable, like ''@question'', and then print that,
or if i have to do
>>>something like make @question into an intermediary object, like
>>>''question'', and then do something like
''question.question'' to make it
>>>print out. Actually, if somebody could just tell me that, even if
you
>>>don''t know how to do the random thing, it would be
appreciated.
>>>
>>>Thanks!
>>
>>Hi,
>>
>>To select a specific row you use Model.find(id), where model stands for
>>the class that represents your question-answer table. So you could try
>>this out by something like
>>@entry = YourModel.find(id_you_know_that_exists)
>>and in the view display the question like <%= @entry.question %>
>>
>>To pick a random question you could try first retrieving all entries
> 
>>from that table, then picking a random one from them, like
> 
>>entries = YourModel.find(:all)
>>@entry = entries[rand(entries.size-1)]
>>
>>However, if this table is going to be huge this approach would be very
>>inefficient, just giving you a hint for the easiest way to start with it
>>:)
>>
>>--
>>Agnieszka
>>
>>--
>>Posted via http://www.ruby-forum.com/.
>>_______________________________________________
>>Rails mailing list
>>Rails@lists.rubyonrails.org
>>http://lists.rubyonrails.org/mailman/listinfo/rails
> 
> 
> 
> Mikkel Bruun
> 
> www.strongside.dk    - Football Portal(DK)
> ting.minline.dk      - Buy Old Stuff!(DK)
> 
> 
>

Hello Everyone,
    Well, not really knowing rails that in depth yet, but, knowing sql,
you could always do something like;

    select name, random() from Model order by 2; (for postgresql)
  
    different database''s will have different names for the random()
function (Sybase/MS-SQL would use rand() for example). However, this has
distinct advantages over returning the entire result set and doing the
randomization in rails (think large tables).

    I would be interested in seeing how to do this in rails - of course ;)
    Regards
    Stef

Ben Munat wrote:
> Mikkel Bruun wrote:
>>
>> size = Model.count
>
>> obj= Model.find(rand(size+))
>>
>> Assuming the ID''s are sequential...
>
> Yeah... if rows get deleted, the IDs won''t be reused so there will
be
> gaps. This seems problematic. Sucks to pull all rows, but Tim''s
> approach might be safest.
>
> b
>
>> On Monday, April 03, 2006, at 12:29 PM, Agnieszka Figiel wrote:
>>
>>> sean colquhoun wrote:
>>>
>>>> Hi guys. Total newbie here. I''ve been doing web stuff
since 1996 but
>>>> only began the foray into scripting last year. I
haven''t got my skull
>>>> completely 360 degrees around OOP yet. It''s just me
here (in Japan)
>>>> and
>>>> there are no Ruby groups in my area (never mind any in
English).
>>>>
>>>> I''ve got a database table - real simple: question,
answer, and id
>>>> fields
>>>> - and I want to pick one question out randomly and output to
the HTML
>>>> page. Right now I can''t even get single entries out -
all I can do is
>>>> copy and paste from the scaffolding, so it''s every
question or no
>>>> questions at this point. I''m not sure if you can put
the value into a
>>>> variable, like ''@question'', and then print
that, or if i have to do
>>>> something like make @question into an intermediary object, like
>>>> ''question'', and then do something like
''question.question'' to make it
>>>> print out. Actually, if somebody could just tell me that, even
if you
>>>> don''t know how to do the random thing, it would be
appreciated.
>>>>
>>>> Thanks!
>>>
>>> Hi,
>>>
>>> To select a specific row you use Model.find(id), where model stands
for
>>> the class that represents your question-answer table. So you could
try
>>> this out by something like
>>> @entry = YourModel.find(id_you_know_that_exists)
>>> and in the view display the question like <%= @entry.question
%>
>>>
>>> To pick a random question you could try first retrieving all
entries
>>
>>> from that table, then picking a random one from them, like
>>
>>> entries = YourModel.find(:all)
>>> @entry = entries[rand(entries.size-1)]
>>>
>>> However, if this table is going to be huge this approach would be
very
>>> inefficient, just giving you a hint for the easiest way to start
>>> with it
>>> :)
>>>
>>> -- 
>>> Agnieszka
>>>
>>> -- 
>>> Posted via http://www.ruby-forum.com/.
>>> _______________________________________________
>>> Rails mailing list
>>> Rails@lists.rubyonrails.org
>>> http://lists.rubyonrails.org/mailman/listinfo/rails
>>
>>
>>
>> Mikkel Bruun
>>
>> www.strongside.dk    - Football Portal(DK)
>> ting.minline.dk      - Buy Old Stuff!(DK)
>>
>>
>>
> _______________________________________________
> Rails mailing list
> Rails@lists.rubyonrails.org
> http://lists.rubyonrails.org/mailman/listinfo/rails
>

> To select a specific row you use Model.find(id), where model stands for 
> the class that represents your question-answer table. So you could try 
> this out by something like
> @entry = YourModel.find(id_you_know_that_exists)
> and in the view display the question like <%= @entry.question %>
> 
> To pick a random question you could try first retrieving all entries 
> from that table, then picking a random one from them, like
> entries = YourModel.find(:all)
> @entry = entries[rand(entries.size-1)]
> --
> Agnieszka
Thanks!

-- 
Posted via http://www.ruby-forum.com/.

So sorry to keep bothering you guys with really basic stuff, but i
can''t
get it to work. Here''s the function in my controller:

def ask
    all_questions = Question.find(:all)
    @question = all_questions[rand(all_questions.size-1)]
end

...and here''s the code in my "ask.rhtml" file:

 <%= @question.question %>

The way I''ve got it figured out in my head is this: you put the data 
from the database into a variable in the controller (@question). Only it 
isn''t really a variable, it''s an object. But we talk about it
like it''s
a variable for some reason. Anyway, that object automatically takes the 
column names of the DB as its methods. So if I type in 
"@question.question", what I''m telling Rails is: put the
contents of the
"question" column from the single row that I''ve loaded the
@question
variable up with here.
Am i missing a piece somewhere? It looks like it should work, but Rails 
keeps sending me ''nil'' errors.

-- 
Posted via http://www.ruby-forum.com/.

It''s probably not a good idea to have a column in your table called
question
since this is the name of your model.

Try calling the field a different name eg body
then @question.body

Hope it works for you

On 4/4/06, sean colquhoun <seancolquhoun@gk-a.com>
wrote:
>
> So sorry to keep bothering you guys with really basic stuff, but i
can''t
> get it to work. Here''s the function in my controller:
>
> def ask
>     all_questions = Question.find(:all)
>     @question = all_questions[rand(all_questions.size-1)]
> end
>
> ...and here''s the code in my "ask.rhtml" file:
>
> <%= @question.question %>
>
> The way I''ve got it figured out in my head is this: you put the
data
> from the database into a variable in the controller (@question). Only it
> isn''t really a variable, it''s an object. But we talk
about it like it''s
> a variable for some reason. Anyway, that object automatically takes the
> column names of the DB as its methods. So if I type in
> "@question.question", what I''m telling Rails is: put the
contents of the
> "question" column from the single row that I''ve loaded
the @question
> variable up with here.
> Am i missing a piece somewhere? It looks like it should work, but Rails
> keeps sending me ''nil'' errors.
>
> --
> Posted via http://www.ruby-forum.com/.
> _______________________________________________
> Rails mailing list
> Rails@lists.rubyonrails.org
> http://lists.rubyonrails.org/mailman/listinfo/rails
>
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Daniel ----- wrote:
> It''s probably not a good idea to have a column in your table
called
> question
> since this is the name of your model.
> 
> Try calling the field a different name eg body
> then @question.body
> 
> Hope it works for you
Sorry. Didn''t work, so i tried bringing it down to the simplest level 
possible and working up from there, and I''m convinced that
there''s some
fundamental piece of information that i''m missing. Could somebody clue 
me in? For example, here''s the DEF in the controller. All i want it to 
do is print my name to the HTML file:

def ask
    @booyah = ''sean''
end

...and in ''ask.rhtml'':

<%= @booyah %>

That''s it. It doesn''t get any simpler and yet I still
can''t get it to
work. Please, somebody kick me.

-- 
Posted via http://www.ruby-forum.com/.

When you just point your browser to

http://localhost:3000
(assuming webrik on port 3000)

do you see anything?

On 4/4/06, sean colquhoun <seancolquhoun@gk-a.com>
wrote:
>
> Daniel ----- wrote:
> > It''s probably not a good idea to have a column in your table
called
> > question
> > since this is the name of your model.
> >
> > Try calling the field a different name eg body
> > then @question.body
> >
> > Hope it works for you
>
> Sorry. Didn''t work, so i tried bringing it down to the simplest
level
> possible and working up from there, and I''m convinced that
there''s some
> fundamental piece of information that i''m missing. Could somebody
clue
> me in? For example, here''s the DEF in the controller. All i want
it to
> do is print my name to the HTML file:
>
> def ask
>     @booyah = ''sean''
> end
>
> ...and in ''ask.rhtml'':
>
> <%= @booyah %>
>
> That''s it. It doesn''t get any simpler and yet I still
can''t get it to
> work. Please, somebody kick me.
>
> --
> Posted via http://www.ruby-forum.com/.
> _______________________________________________
> Rails mailing list
> Rails@lists.rubyonrails.org
> http://lists.rubyonrails.org/mailman/listinfo/rails
>
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Daniel ----- wrote:
> When you just point your browser to
> 
> http://localhost:3000
> (assuming webrik on port 3000)
> 
> do you see anything?
That''s exactly which port I''ve got it on, and I see the
standard "You''ve
got Rails running!" or something like that, so the server''s OK.
When I
go to /questions, which is the controller name, I get zero. Unless I put 
in something invalid. Then I get an error message. So at least I know 
that Rails is paying attention.

Do I need more pieces to the puzzle, maybe? I mean, all I''ve got is a 
controller and a view. I''m not even using data; all I''m doing
is putting
a value into a variable/object and then asking for it out again; so I 
wouldn''t think that I would need anything like that. I even tried 
changing my variable names: @booyah, $booyah, and booyah all come up 
with nothing. I even tried treating @booyah like an array and typing 
@booyah[0], but I got a ''nil object'' error.

-- 
Posted via http://www.ruby-forum.com/.

On Apr 3, 2006, at 11:38 PM, sean colquhoun wrote:
> Daniel ----- wrote:
>> When you just point your browser to
>>
>> http://localhost:3000
>> (assuming webrik on port 3000)
>>
>> do you see anything?
>
> That''s exactly which port I''ve got it on, and I see the
standard
> "You''ve
> got Rails running!" or something like that, so the server''s
OK. When I
> go to /questions, which is the controller name, I get zero. Unless  
> I put
> in something invalid. Then I get an error message. So at least I know
> that Rails is paying attention.
>
> Do I need more pieces to the puzzle, maybe? I mean, all I''ve got
is a
> controller and a view. I''m not even using data; all I''m
doing is
> putting
> a value into a variable/object and then asking for it out again; so I
> wouldn''t think that I would need anything like that. I even tried
> changing my variable names: @booyah, $booyah, and booyah all come up
> with nothing. I even tried treating @booyah like an array and typing
> @booyah[0], but I got a ''nil object'' error.
I think you need questions/ask

It''s controller/action

-- 
-- Tom Mornini

> I think you need questions/ask
> 
> It''s controller/action
> 
> --
> -- Tom Mornini
Awesome! That wasn''t exactly the problem, but you got me looking in the
right place. You know what it was? I had ''ask'' set up as my
index
action. I did this just by modifying the scaffold, so what I got was:

  def index
    list
    render :action => ''ask''
  end

Anyway, when I was thinking about changing the index action back to list 
so that I could access the thing with questions/ask, i noticed that the 
2nd line said ''list'' still. So I changed it to
''ask'' and it worked!

Wait. I get it now. The 2nd line is the actual call; the 3rd line tells 
Rails to render the call. I thought that the call to render was the 
whole thing. Sorry to take your time, guys.

-- 
Posted via http://www.ruby-forum.com/.

Problem here is that your controller renders your model, not the other
way around.  You want to call ''ask'' in your controller, which
will
then render ask.rhtml

If your controller is named ''asdf'', you should hit
http://localhost:3000/asdf/ask to see what happens when you run the
ask method of the asdf controller.

Regards

Dave M.

On 04/04/06, sean colquhoun <seancolquhoun@gk-a.com>
wrote:
> Daniel ----- wrote:
> > It''s probably not a good idea to have a column in your table
called
> > question
> > since this is the name of your model.
> >
> > Try calling the field a different name eg body
> > then @question.body
> >
> > Hope it works for you
>
> Sorry. Didn''t work, so i tried bringing it down to the simplest
level
> possible and working up from there, and I''m convinced that
there''s some
> fundamental piece of information that i''m missing. Could somebody
clue
> me in? For example, here''s the DEF in the controller. All i want
it to
> do is print my name to the HTML file:
>
> def ask
>     @booyah = ''sean''
> end
>
> ...and in ''ask.rhtml'':
>
> <%= @booyah %>
>
> That''s it. It doesn''t get any simpler and yet I still
can''t get it to
> work. Please, somebody kick me.
>
> --
> Posted via http://www.ruby-forum.com/.
> _______________________________________________
> Rails mailing list
> Rails@lists.rubyonrails.org
> http://lists.rubyonrails.org/mailman/listinfo/rails
>