Noob needs help with 'if' block

danielr · March 12, 2006, 12:30am

Hello all. I’m a noob at Ruby on Rails, only started learning a few days
ago, but I’m loving it so far. I do have a few years experience with
PHP, ASP, MySQL, etc., so I’m not totally clueless, though.

Anyway, I’m having trouble with something that should be fairly trivial:
I have an ‘if’ statement that is supposed to print out a table row if a
vriable is either nil, or matches another specific value (like the
Rolling with Rails tutorial example). Unfortunately, it only works
halfway. It will print the table rows if the variable is nil, but if the
variable has any valu in it at all, it prints nothing, even when it
matches the other value. I’ve been banging my head against this for
about an hour now, and I think it’s one of those things where I can’t
see it because it’s too simple, so I’m hoping that maybe one of you can
tell me what’s wrong by looking at the code? Here’s the code I’m using:

<% @carttransactions.each do |carttransaction| %>
<%= @cartno %><%= carttransaction.cart.id %>
<% if (@cartno == nil ) || (@cartno == carttransaction.cart.id ) %>

<% for column in Carttransaction.content_columns %> <%=h carttransaction.send(column.name) %> <% end %> <%= link_to 'Show', :action => 'show', :id => carttransaction %> <%= link_to 'Edit', :action => 'edit', :id => carttransaction %> <%= link_to 'Destroy', { :action => 'destroy', :id => carttransaction }, :confirm => 'Are you sure?' %> <% end %> <% end %> ----------------------------------------------

When I access the page with
‘http://localhost:3000/carttransaction/list’, it displays the table rows
perfectly. However, if I try
‘http://localhost:3000/carttransaction/list?cartno=1’, it displays none
of the rows, not even the ones where ‘carttransaction.cart.id’ equals 1.
You’ll notice the line
‘<%= @cartno %><%= carttransaction.cart.id %>’
up there, I put that in to make sure that, indeed, both vars were there
and their values matched, and the page prints them both out and shows
that @cartno is, indeed, receiving the value from the URL, and that the
other one also has its value… so, any ideas at all? I’m stumped.

danielr · March 12, 2006, 12:40am

I must admit I skimmed through your email, but it looks like you
should maybe look into using a partial here. Will make your code much
cleaner and easier to read.

<%= render(:partial => "transaction", :collection => @carttransactions %>

_transaction.rhtml


<tr>
  <td><!-- DISPLAY FOR AN INDIVIDUAL TRANSACTION HERE --></td>
</tr>

Again this is just a general rails tip...

~ Ben

On 3/11/06, Daniel R. <[email protected]> wrote:
> matches the other value. I've been banging my head against this for
> <td><%=h carttransaction.send(column.name) %></td>
> ----------------------------------------------
> that @cartno is, indeed, receiving the value from the URL, and that the
> other one also has its value.. so, any ideas at all? I'm stumped.
>
> --
> Posted via http://www.ruby-forum.com/.
> _______________________________________________
> Rails mailing list
> [email protected]
> http://lists.rubyonrails.org/mailman/listinfo/rails
>


--
Ben R.
http://www.benr75.com

danielr · March 12, 2006, 12:52am

Thanks for the tip, Ben, I’ll look into it; I can see several places in
my app where the use of a partial would clean things up considerably.
However, this doesn’t address my initial problem: that the ‘if’
statement doesn’t seem to be evaluating right. It runs fine if the first
condition in the ‘or’ pair is true, but doesn’t run if the second
condition is true, even though it should. Any ideas?

-Daniel

Ben R. wrote:

I must admit I skimmed through your email, but it looks like you
should maybe look into using a partial here. Will make your code much
cleaner and easier to read.
<%= render(:partial => "transaction", :collection => @carttransactions %>
_transaction.rhtml
<tr>
  <td></td>
</tr>

Again this is just a general rails tip...

~ Ben

danielr · March 12, 2006, 1:13am

Hi Daniel,

I’m pretty new to this too, but I think the problem may be in the second
line.

<%= @cartno %><%= carttransaction.cart.id %>

should be…

<%= @cartno = carttransaction.cart.id %>

Or maybe not Let us know.

Best regards,
Bill

----- Original Message -----
From: “Daniel R.” [email protected]
To: [email protected]
Sent: 2006-03-11 5:30 PM
Subject: [Rails] Noob needs help with ‘if’ block

danielr · March 12, 2006, 1:21am

Daniel,

I suggest to change
<% if (@cartno == nil ) || (@cartno == carttransaction.cart.id ) %>
for
<% if (@cartno == carttransaction.cart.id) || !@cartno %>
And then try again

This approach depends on you Database schema… if most of your fields
are null, then I will suggest to change !@cartno to the other side of
the ||. Normally you don’t want to have many null values on your
database (if you have many null values means that probably your schema
needs to be changed unless you have designed that way )

Anyway, I don’t know if this solve your problem but give at least give
you a hint on other places to looks at

Cheers,

Rafa

Bill W. wrote:

Hi Daniel,

I’m pretty new to this too, but I think the problem may be in the second
line.

<%= @cartno %><%= carttransaction.cart.id %>

should be…

<%= @cartno = carttransaction.cart.id %>

Or maybe not Let us know.

Best regards,
Bill

----- Original Message -----
From: “Daniel R.” [email protected]
To: [email protected]
Sent: 2006-03-11 5:30 PM
Subject: [Rails] Noob needs help with ‘if’ block

danielr · March 12, 2006, 2:38am

Thanks for the help so far, but still no luck:

Bill: Actually, that line is there simply to print out the values of
@cartno and carttransaction.cart.id so I can see that they have the
right values, I’m going to delete that line before I go into production.
I’ve tried running the app without that line as well, doesn’t make a
difference.

Rath: I tried changing that line of code as you suggested, but it still
does the same thing. And the way you suggested is fine the databse
doesn’t have many null values, @cartno comes in from an URL parameter.

Any more ideas? I’m gonna keep trying to figure it out as well, if I
manage to figure out what’s wrong, I’ll post it here.

-Daniel

Rath wrote:

Daniel,

I suggest to change
<% if (@cartno == nil ) || (@cartno == carttransaction.cart.id ) %>
for
<% if (@cartno == carttransaction.cart.id) || !@cartno %>
And then try again

This approach depends on you Database schema… if most of your fields
are null, then I will suggest to change !@cartno to the other side of
the ||. Normally you don’t want to have many null values on your
database (if you have many null values means that probably your schema
needs to be changed unless you have designed that way )

Anyway, I don’t know if this solve your problem but give at least give
you a hint on other places to looks at

Cheers,

Rafa

Bill W. wrote:

Hi Daniel,

I’m pretty new to this too, but I think the problem may be in the second
line.

<%= @cartno %><%= carttransaction.cart.id %>

should be…

<%= @cartno = carttransaction.cart.id %>

Or maybe not Let us know.

Best regards,
Bill

----- Original Message -----
From: “Daniel R.” [email protected]
To: [email protected]
Sent: 2006-03-11 5:30 PM
Subject: [Rails] Noob needs help with ‘if’ block

danielr · March 12, 2006, 2:57am

On 3/11/06, Daniel R. [email protected] wrote:

matches the other value. I’ve been banging my head against this for
about an hour now, and I think it’s one of those things where I can’t
see it because it’s too simple, so I’m hoping that maybe one of you can
tell me what’s wrong by looking at the code? Here’s the code I’m using:

<% @carttransactions.each do |carttransaction| %>
<%= @cartno %><%= carttransaction.cart.id %>

Try wrapping those. Maybe they only ‘look’ equal.

<%= ‘|’ + @cartno.to_s + ‘|’ %><%= ‘|’ + carttransaction.cart.id.to_s +
‘|’ %>

<% if (@cartno == nil ) || (@cartno == carttransaction.cart.id ) %>

'<%= @cartno %><%= carttransaction.cart.id %>' http://lists.rubyonrails.org/mailman/listinfo/rails

–
Bill G. (aka aGorilla)
The best answer to most questions is “it depends”.

danielr · March 12, 2006, 2:46am

Have you tried to use the “console” script and check it from there?

open a promt on the root directory and type
root> ruby script/console

You can debug your program from there… it isn’t perfect but sometimes
it is really useful to use this command

Cheers,

Rafa

danielr · March 12, 2006, 3:26am

Well, finaly found the problem!

They ‘looked’ equal, but apparently, it was seeing one var as a string
and another as something else. I checked in the database, and both the
‘id’ field in table ‘carts’ and the ‘cart_id’ field in table
‘carttransactions’ are set as int(11), but, apparently, at some point
one of the variables I’m using for comparison stops being an int. (My
guess is ‘@cartno’, since it comes as an URL parameter, is read as a
string, while ‘carttransaction.cart.id’, coming straight from the
database, is read as an int).

I fixed it by adding .to_s to both variables in the comparison (and
doing some changes as suggested earlier), so that
<% if (@cartno == nil ) || (@cartno == carttransaction.cart.id ) %>

becomes, instead:

<% if (@cartno.to_s == carttransaction.cart.id.to_s) || !@cartno %>

Now it works flawlessly.

Thanks muchly for everyone’s help and suggestions, and especially to
Bill G. for pointing me in the right direction.

-Daniel

Bill G. wrote:

On 3/11/06, Daniel R. [email protected] wrote:

matches the other value. I’ve been banging my head against this for
about an hour now, and I think it’s one of those things where I can’t
see it because it’s too simple, so I’m hoping that maybe one of you can
tell me what’s wrong by looking at the code? Here’s the code I’m using:

<% @carttransactions.each do |carttransaction| %>
<%= @cartno %><%= carttransaction.cart.id %>

Try wrapping those. Maybe they only ‘look’ equal.

<%= ‘|’ + @cartno.to_s + ‘|’ %><%= ‘|’ + carttransaction.cart.id.to_s +
‘|’ %>

<% if (@cartno == nil ) || (@cartno == carttransaction.cart.id ) %>

'<%= @cartno %><%= carttransaction.cart.id %>' http://lists.rubyonrails.org/mailman/listinfo/rails

–
Bill G. (aka aGorilla)
The best answer to most questions is “it depends”.

danielr · March 12, 2006, 11:32pm

Daniel,

I’d suggest, in the interests of making your code a little less PHP-
ish and a bit more Ruby-ish:

<% if @cartno.to_i == carttransaction.cart.id or @cartno.nil? %>

Cheers,

Pete Y.

danielr · March 13, 2006, 3:42am

Heh, is it that obvious that I’ve mostly worked in PHP till now?

Thanks for the tip, I’ll try that out, looks good!

-Daniel

Pete Y. wrote:

Daniel,

I’d suggest, in the interests of making your code a little less PHP-
ish and a bit more Ruby-ish:

<% if @cartno.to_i == carttransaction.cart.id or @cartno.nil? %>

Cheers,

Pete Y.

danielr · March 13, 2006, 3:59am

If I read this thread correctly, one of the terms in the comparison came
from “a URL parameter.” Because params and other querystring data
contain no metadata, they are always represented as strings initially.
One good way to see what’s going on is:

tail -f log/development.log

as you pop around in the browser, you will have all the information you
need, including the entire params hash for each request. That would
probably have given you the clue you needed.

Two other ways I find handy to debug things like this are:

<%= debug(var) %>

and

logger.debug “var[#{var}] isa: #{var.class}”

Hope this helps in the future.

Daniel R. wrote:

Heh, is it that obvious that I’ve mostly worked in PHP till now?

Thanks for the tip, I’ll try that out, looks good!

-Daniel

Pete Y. wrote:

Daniel,

I’d suggest, in the interests of making your code a little less PHP-
ish and a bit more Ruby-ish:

<% if @cartno.to_i == carttransaction.cart.id or @cartno.nil? %>

Cheers,

Pete Y.