Forum: Ruby on Rails find_by_sql - ActiveRecord - Help please.

I am new to the language and trying to add a couple of simple tests on
user input, followed by a DB query, then using the returned values
(where the problem lies)

I first run a find_by_sql similar to this

@my_names = modelname.find_by_sql

I then check to see if NO returns via

if @my_names.size == 0

==================

My question is, how do I access the values that are now in the array. I
seem to be able to set session variables by way of

session[:whatever] = @my_names[0].column_name
etc..

but am unable to perform a if construct that looks like

if @my_names[0].column_name == "TEST VALUE"

I keep getting an undefined method error when I try to run the code.
Thanks very much in advance for any assistance with this.

On 7 November 2012 20:07, Jeff Lockyer <lists@ruby-forum.com> wrote:
> I am new to the language and trying to add a couple of simple tests on
> user input, followed by a DB query, then using the returned values
> (where the problem lies)
>
> I first run a find_by_sql similar to this
>
> @my_names = modelname.find_by_sql

I know this is not part of your question, but as a newcommer to rails
I think it is very unlikely that you should be using find_by_sql.
There are not many situations that this is necessary, there is almost
certainly another way.  You might like to ask about this in another
thread to see if there is a better way.

> session[:whatever] = @my_names[0].column_name
> etc..
>
> but am unable to perform a if construct that looks like
>
> if @my_names[0].column_name == "TEST VALUE"
>
> I keep getting an undefined method error when I try to run the code.
> Thanks very much in advance for any assistance with this.

Show us the actual code and the full error message please.  First look
carefully at the error and try to interpret it, often the clue is in
the message but may not be initially obvious to a newcommer.

Finally, if you have not already done so, I recommend working through
a good tutorial on rails.  railstutorial.org is good and is free to
use online.  Make sure that you use a tutorial for rails 3 and that
you use exactly the right version of rails.

Colin

Hi Colin,

This is old code (Rails v 1.1.6 - Ruby 1.8.5) that I am working with, 
and don't want to migrate it too to current version because it is not 
long term.

The code is almost exactly as cited above, just have the column names 
removed.
The error code tells me that

NoMethodError (undefined method `province' for nil:NilClass):
    /path/file.rb:302:in `set_no'

So I look on that line, in the set_no definition, which is where I was 
trying to call this line

if @my_names[0].province == "XX"

province is one of the column names that is returned from the 
find_by_sql call.

Does this make any more sense now ? I have been through many attempts to 
resolve this, and can work with parameters, etc but with DB returns it 
seems I am missing something.

Colin Law wrote in post #1083450:
> On 7 November 2012 20:07, Jeff Lockyer <lists@ruby-forum.com> wrote:
>> I am new to the language and trying to add a couple of simple tests on
>> user input, followed by a DB query, then using the returned values
>> (where the problem lies)
>>
>> I first run a find_by_sql similar to this
>>
>> @my_names = modelname.find_by_sql
>
> I know this is not part of your question, but as a newcommer to rails
> I think it is very unlikely that you should be using find_by_sql.
> There are not many situations that this is necessary, there is almost
> certainly another way.  You might like to ask about this in another
> thread to see if there is a better way.
>
>> session[:whatever] = @my_names[0].column_name
>> etc..
>>
>> but am unable to perform a if construct that looks like
>>
>> if @my_names[0].column_name == "TEST VALUE"
>>
>> I keep getting an undefined method error when I try to run the code.
>> Thanks very much in advance for any assistance with this.
>
> Show us the actual code and the full error message please.  First look
> carefully at the error and try to interpret it, often the clue is in
> the message but may not be initially obvious to a newcommer.
>
> Finally, if you have not already done so, I recommend working through
> a good tutorial on rails.  railstutorial.org is good and is free to
> use online.  Make sure that you use a tutorial for rails 3 and that
> you use exactly the right version of rails.
>
> Colin

On 7 November 2012 22:06, Jeff Lockyer <lists@ruby-forum.com> wrote:
> NoMethodError (undefined method `province' for nil:NilClass):
>     /path/file.rb:302:in `set_no'
>
> So I look on that line, in the set_no definition, which is where I was
> trying to call this line
>
> if @my_names[0].province == "XX"

As I said, the clue is in the error message.  Undefined method
province for nil:NilClass.  This is saying that you have tried to call
the method province on a nil object, which means that @my_names[0] is
nil.

Colin

Hi Colin,

I don't think it is, in fact I know it isn't empty because the logic is 
inside a test for the return size of 0.

   if @my_names.size == 0

                render :update do |page|
                // Bunch of updating code to the displayed message to 
indicate no match found.
                page[:name].visualEffect('highlight')
                end

        else

           // This is where I try to test the code of

          if @my_names[0].province == "XX"

          // Then want to do some other things.

          else
          // Set sessions variables.

          session[:var_a] = @my_names
          session[:var_b] = @my_names[0].first_name
          session[:var_c] = @my_names[0].last_name
          session[:var_d] = @my_names[0].line_1
          session[:var_d] = (@my_names[0].line_2 || '')
          session[:var_e] = (@my_names[0].province || '')

----------

Any thoughts ? It doesn't seem to matter if I test AFTER the initial 
test for 0 or before (knowing that I am going to get a match because of 
predefined values that exist in the database.) I always get the same 
error. Thanks again in advance.

Colin Law wrote in post #1083465:
> On 7 November 2012 22:06, Jeff Lockyer <lists@ruby-forum.com> wrote:
>> NoMethodError (undefined method `province' for nil:NilClass):
>>     /path/file.rb:302:in `set_no'
>>
>> So I look on that line, in the set_no definition, which is where I was
>> trying to call this line
>>
>> if @my_names[0].province == "XX"
>
> As I said, the clue is in the error message.  Undefined method
> province for nil:NilClass.  This is saying that you have tried to call
> the method province on a nil object, which means that @my_names[0] is
> nil.
>
> Colin

On Wed, Nov 7, 2012 at 2:49 PM, Jeff Lockyer <lists@ruby-forum.com> 
wrote:

> I don't think it is, in fact I know it isn't empty because the logic is
> inside a test for the return size of 0.

1.9.3 (main):0 > @stuff = []
=> []
1.9.3 (main):0 > @stuff << nil
=> [
  [0] nil
]
1.9.3 (main):0 > @stuff[0]
=> nil
1.9.3 (main):0 > @stuff.size
=> 1
1.9.3 (main):0 >

You might want to try a different approach to validating the content
of your array :-)

--
Hassan Schroeder ------------------------ hassan.schroeder@gmail.com
http://about.me/hassanschroeder
twitter: @hassan

Another example:


data = Array.new(10, nil)
p data

--output:--
[nil, nil, nil, nil, nil, nil, nil, nil, nil, nil]

p data.size

--output:--
10

puts data[0].province

--output:--
1.rb:4:in `<main>': undefined method `province' for nil:NilClass 
(NoMethodError)

On 7 November 2012 22:49, Jeff Lockyer <lists@ruby-forum.com> wrote:
>                 page[:name].visualEffect('highlight')
>                 end

This end would appear to close the if statement.

>
>         else

I am surprised that does not cause a syntax error.
Also as others have pointed out the first element of the array could be 
nil.

Colin

The "end" closes the "render :update do |page| "

On 8 November 2012 12:56, Timster <timshaffer00@gmail.com> wrote:
> The "end" closes the "render :update do |page| "

Good job someone is paying proper attention.

Colin