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Craig Beck

2005-May-24 07:28 UTC

associations basics

I''m driving myself nuts with this annoying bug that I just
don''t get.

I have a users table/model and a tickets table/model. Something like  
this:

     users (
         id int primary key auto_increment,
         first_name varchar(20),
         last_name varchar(20)
         )

     tickets (
         id primary key auto_increment,
         user_id int,
         created_on datetime
         )

     ticket.rb
         belongs_to :users

     user.rb
         has_many :tickets

The problem I''m having is trying to access the user data when showing  
the tickets like so:

     <% @tickets.each do |ticket| %>
         <%= ticket.user.id %>
         <%= ticket.user.first_name %>
         <%= ticket.user.inspect %>
     <% end %>

When I access ticket.user.id there''s no problem, but when I try  
ticket.user.first_name it throws an undefined method `last_name'' for  
nil:NilClass exception. When I use ticket.user.inspect all the right  
data is there -- so what am I not getting about this? What''s missing?

And I can''t seem to find, although I know I came across it before,  
but how can I add a virtual accessor to the class like

     def self.full_name
         return self.first_name << " " << self.last_name
     end

as I''m getting the same errors when I use the above method.

Thanks,

--
Craig Beck
http://blog.rebelplatoon.com
http://luckybonza.com
AIM: Kreiggers




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Joe Van Dyk

2005-May-24 07:42 UTC

head link

Re: associations basics

On 5/24/05, Craig Beck <craigbeck-sUNYKzuJffo33s2pWanAEQ@public.gmane.org>
wrote:> I''m driving myself nuts with this annoying bug that I just
don''t get.
> 
> I have a users table/model and a tickets table/model. Something like this:
> 
>     users (
>         id int primary key auto_increment,
>         first_name varchar(20),
>         last_name varchar(20)
>         )
> 
>     tickets (
>         id primary key auto_increment,
Probably unrelated, but try giving that column type ''int'' like
the users table.
>         user_id int,
>         created_on datetime
>         )
> 
>     ticket.rb 
>         belongs_to :users
belongs_to :user
> 
>     user.rb
>         has_many :tickets
> 
> The problem I''m having is trying to access the user data when
showing the
> tickets like so:
> 
>     <% @tickets.each do |ticket| %>
>         <%= ticket.user.id %>
>         <%= ticket.user.first_name %>
>         <%= ticket.user.inspect %>
>     <% end %>
>  
> 
> When I access ticket.user.id there''s no problem, but when I try
> ticket.user.first_name it throws an undefined method `last_name''
for
> nil:NilClass exception. When I use ticket.user.inspect all the right data
is
> there -- so what am I not getting about this? What''s missing?
You sure that ticket.user.id is giving you the RIGHT id?  

> 
> And I can''t seem to find, although I know I came across it before,
but how
> can I add a virtual accessor to the class like
> 
>     def self.full_name
>         return self.first_name << " " <<
self.last_name
>     end
> 
> as I''m getting the same errors when I use the above method.
You probably don''t want to make a class function.

So you''d have

def full_name
  return first_name << " " << last_name     
  # or return self.first_name << " " << self.last_name
  # not sure which is better
end

And use it like
user = User.find(.... )
user.full_name



Joe

Craig Beck

2005-May-24 10:07 UTC

head link

Re: associations basics

On May 24, 2005, at 12:42 AM, Joe Van Dyk wrote:
> On 5/24/05, Craig Beck
<craigbeck-sUNYKzuJffo33s2pWanAEQ@public.gmane.org> wrote:
>
>> I''m driving myself nuts with this annoying bug that I just
don''t get.
>>
>> I have a users table/model and a tickets table/model. Something  
>> like this:
>>
>>     users (
>>         id int primary key auto_increment,
>>         first_name varchar(20),
>>         last_name varchar(20)
>>         )
>>
>>     tickets (
>>         id primary key auto_increment,
>>
>
> Probably unrelated, but try giving that column type ''int''
like the
> users table.
>
> belongs_to :user
Sorry, I should have specified -- pseudo code. Not exactly what the  
sql is to create the table, but he general idea anyway.
>>
>>     user.rb
>>         has_many :tickets
>>
>> The problem I''m having is trying to access the user data when
>> showing the
>> tickets like so:
>>
>>     <% @tickets.each do |ticket| %>
>>         <%= ticket.user.id %>
>>         <%= ticket.user.first_name %>
>>         <%= ticket.user.inspect %>
>>     <% end %>
>>
>>
>> When I access ticket.user.id there''s no problem, but when I
try
>> ticket.user.first_name it throws an undefined method
`last_name'' for
>> nil:NilClass exception. When I use ticket.user.inspect all the  
>> right data is
>> there -- so what am I not getting about this? What''s missing?
>>
>
> You sure that ticket.user.id is giving you the RIGHT id?
Yes -- the id is correct. As I said, when I use ticket.user.inspect,  
the correct values are there but if I try to access them directly  
then I get an exception. The exception is when I access the id --  
which works just fine, but isn''t particularly helpful.
>> And I can''t seem to find, although I know I came across it
before,
>> but how
>> can I add a virtual accessor to the class like
>>
>>     def self.full_name
>>         return self.first_name << " " <<
self.last_name
>>     end
>>
>> as I''m getting the same errors when I use the above method.
>
> You probably don''t want to make a class function.
>
> So you''d have
>
> def full_name
>   return first_name << " " << last_name
>   # or return self.first_name << " " <<
self.last_name
>   # not sure which is better
> end
>
> And use it like
> user = User.find(.... )
> user.full_name
Oh, so I have it backwards?

def self.some_method makes a class mathod and def some_method makes  
an instance method?


--
Craig Beck
http://blog.rebelplatoon.com
http://luckybonza.com
AIM: Kreiggers




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Craig Beck

2005-May-24 20:08 UTC

head link

Re: associations basics

On May 24, 2005, at 3:07 AM, Craig Beck wrote:
>
> On May 24, 2005, at 12:42 AM, Joe Van Dyk wrote:
>
>> On 5/24/05, Craig Beck
<craigbeck-sUNYKzuJffo33s2pWanAEQ@public.gmane.org> wrote:
>>
>>> I''m driving myself nuts with this annoying bug that I just
don''t
>>> get.
>>>
>>> I have a users table/model and a tickets table/model. Something  
>>> like this:
>>>
>>>     users (
>>>         id int primary key auto_increment,
>>>         first_name varchar(20),
>>>         last_name varchar(20)
>>>         )
>>>
>>>     tickets (
>>>         id primary key auto_increment,
>>>
>>
>> Probably unrelated, but try giving that column type
''int'' like the
>> users table.
>>
>
>> belongs_to :user
>
> Sorry, I should have specified -- pseudo code. Not exactly what the  
> sql is to create the table, but he general idea anyway.
>
>>>
>>>     user.rb
>>>         has_many :tickets
>>>
>>> The problem I''m having is trying to access the user data
when
>>> showing the
>>> tickets like so:
>>>
>>>     <% @tickets.each do |ticket| %>
>>>         <%= ticket.user.id %>
>>>         <%= ticket.user.first_name %>
>>>         <%= ticket.user.inspect %>
>>>     <% end %>
>>>
>>>
>>> When I access ticket.user.id there''s no problem, but when
I try
>>> ticket.user.first_name it throws an undefined method
`last_name'' for
>>> nil:NilClass exception. When I use ticket.user.inspect all the  
>>> right data is
>>> there -- so what am I not getting about this? What''s
missing?
>>>
>>
>> You sure that ticket.user.id is giving you the RIGHT id?
>
> Yes -- the id is correct. As I said, when I use  
> ticket.user.inspect, the correct values are there but if I try to  
> access them directly then I get an exception. The exception is when  
> I access the id -- which works just fine, but isn''t particularly  
> helpful.
Okay, just realised my bonehead mistake -- I didn''t require
"user" in
the ticket_controller.rb file. Problem solved. Amazing what taking a  
break and getting some rest from pounding my head into a wall will do.


--
Craig Beck
http://blog.rebelplatoon.com
http://luckybonza.com
AIM: Kreiggers




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Joe Van Dyk

2005-May-24 20:23 UTC

head link

Re: associations basics

On 5/24/05, Craig Beck <craigbeck-sUNYKzuJffo33s2pWanAEQ@public.gmane.org>
wrote:> 
> 
> On May 24, 2005, at 12:42 AM, Joe Van Dyk wrote:
> 
> On 5/24/05, Craig Beck
<craigbeck-sUNYKzuJffo33s2pWanAEQ@public.gmane.org> wrote:
> 
> I''m driving myself nuts with this annoying bug that I just
don''t get.
> 
> I have a users table/model and a tickets table/model. Something like this:
> 
>     users (
>         id int primary key auto_increment,
>         first_name varchar(20),
>         last_name varchar(20)
>         )
> 
>     tickets (
>         id primary key auto_increment, 
> 
> Probably unrelated, but try giving that column type ''int''
like the users
> table.
> 
> 
> 
> belongs_to :user
> 
> Sorry, I should have specified -- pseudo code. Not exactly what the sql is
> to create the table, but he general idea anyway.
Are you using "belongs_to :user" or "belongs_to :users"?  I
think you
want to the singular version.

> Oh, so I have it backwards?
> 
> def self.some_method makes a class mathod and def some_method makes an
> instance method?
Correct.  You could use def User.full_name instead to make a class
method, I think.

Craig Beck

2005-May-24 22:44 UTC

head link

Re: associations basics

On May 24, 2005, at 3:53 PM, David Teare wrote:
> >> You sure that ticket.user.id is giving you the RIGHT id?
>
> What Joe meant by this is that in ruby nil.id == 4, which can be  
> very confusing.  Add the following code to application_helper.rb to  
> ensure this doesn''t trick you again in the future:
>
>     def nil.id() raise(ArgumentError, "You are calling nil.id!   
> This will result in ''4''!") end
Not sure I''m following you.... are you saying that NilClass has an id  
attribute that could return 4? That seems a bit odd.

But anyway, I don''t believe that''s what is happening as when I
use
ticket.user.id and it returns 4, that''s a valid user.id in the  
database. If I use ticket.user.inspect then I get what I''d expect  
from the database data ex:

     #<User:0x2325afc @attributes={"id"=>"1",
"first_name"=>"Craig",
"last_name"=>"Beck",
"active"=>"1"}

which is exactly right.

Where I''m confused is without using require "user" I can
access the
ticket.user.id attribute just fine, but it would throw an "undefined  
method `last_name'' for nil:NilClass" exception if i tried to
access
ticket.user.last_name (yes, last_name is a column in the db schema).  
But if I just inspect the ticket.user object, all the correct  
attributes are there -- but it doesn''t think it''s a class of
its own?
(hence the NilClass exception)

If I require "user" in the ticket_controller.rb file then everything  
works fine and Rails treats tickets.user as a full fledged User  
object. So I''m guessing Rails is really smart, but not smart enough  
to know when I''m associating to another table that there''s a
model
for that table?

Is there another way I should specify the User model to the  
ticket_controller? perhaps model :user, :ticket, :note  when I know  
tickets have notes and belong to a user?

--
Craig Beck
http://blog.rebelplatoon.com
http://luckybonza.com
AIM: Kreiggers

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David Teare

2005-May-24 22:53 UTC

head link

Re: associations basics

&gt;&gt; You sure that ticket.user.id is giving you the RIGHT id? 

What Joe meant by this is that in ruby nil.id == 4, which can be very
confusing.  Add the following code to application_helper.rb to ensure
this doesn''t trick you again in the future:

    def nil.id() raise(ArgumentError, "You are calling nil.id!  This
will result in ''4''!") end

Joe Van Dyk wrote:

On 5/24/05, Craig Beck  wrote:

I''m driving myself nuts with this annoying bug that I just
don''t get.

I have a users table/model and a tickets table/model. Something like this:

    users (
        id int primary key auto_increment,
        first_name varchar(20),
        last_name varchar(20)
        )

    tickets (
        id primary key auto_increment,

Probably unrelated, but try giving that column type ''int'' like
the users table.

        user_id int,
        created_on datetime
        )

    ticket.rb 
        belongs_to :users

belongs_to :user

    user.rb
        has_many :tickets

The problem I''m having is trying to access the user data when showing
the
tickets like so:

    &lt;% @tickets.each do |ticket| %&gt;
        &lt;%= ticket.user.id %&gt;
        &lt;%= ticket.user.first_name %&gt;
        &lt;%= ticket.user.inspect %&gt;
    &lt;% end %&gt;

When I access ticket.user.id there''s no problem, but when I try
ticket.user.first_name it throws an undefined method `last_name'' for
nil:NilClass exception. When I use ticket.user.inspect all the right data is
there -- so what am I not getting about this? What''s missing?

You sure that ticket.user.id is giving you the RIGHT id?  

And I can''t seem to find, although I know I came across it before, but
how
can I add a virtual accessor to the class like

    def self.full_name
        return self.first_name &lt;&lt; " " &lt;&lt;
self.last_name
    end

as I''m getting the same errors when I use the above method.

You probably don''t want to make a class function.

So you''d have

def full_name
  return first_name &lt;&lt; " " &lt;&lt; last_name
  # or return self.first_name &lt;&lt; " " &lt;&lt;
self.last_name
  # not sure which is better
end

And use it like
user = User.find(.... )
user.full_name

Joe
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Jordan Brock

2005-May-25 05:16 UTC

head link

Re: associations basics

Craig,

RE: nil.id <http://nil.id>, check out the gotcha''s page in the
wiki:

http://wiki.rubyonrails.com/rails/show/Gotcha


On 5/25/05, Craig Beck <craigbeck-sUNYKzuJffo33s2pWanAEQ@public.gmane.org>
wrote:> 
> 
> On May 24, 2005, at 3:53 PM, David Teare wrote:
> 
> >> You sure that ticket.user.id <http://ticket.user.id> is
giving you the
> RIGHT id? 
> 
> What Joe meant by this is that in ruby nil.id <http://nil.id> == 4,
which
> can be very confusing. Add the following code to application_helper.rb to 
> ensure this doesn''t trick you again in the future:
> 
> def nil.id() raise(ArgumentError, "You are calling nil.id
<http://nil.id>!
> This will result in ''4''!") end
> 
> 
> Not sure I''m following you.... are you saying that NilClass has an
idattribute that could return 4? That seems a bit odd.
> 
> But anyway, I don''t believe that''s what is happening as
when I use
> ticket.user.id <http://ticket.user.id> and it returns 4,
that''s a valid
> user.id <http://user.id> in the database. If I use
ticket.user.inspectthen I get what I''d expect from the database data
ex:
> 
> #<User:0x2325afc @attributes={"id"=>"1",
"first_name"=>"Craig",
> "last_name"=>"Beck",
"active"=>"1"}
> 
> which is exactly right. 
> 
> Where I''m confused is without using require "user" I can
access the
> ticket.user.id <http://ticket.user.id> attribute just fine, but it
would
> throw an "undefined method `last_name'' for nil:NilClass"
exception if i
> tried to access ticket.user.last_name (yes, last_name is a column in the 
> db schema). But if I just inspect the ticket.user object, all the correct 
> attributes are there -- but it doesn''t think it''s a class
of its own? (hence
> the NilClass exception)
> 
> If I require "user" in the ticket_controller.rb file then
everything works
> fine and Rails treats tickets.user as a full fledged User object. So
I''m
> guessing Rails is really smart, but not smart enough to know when
I''m
> associating to another table that there''s a model for that table? 
> 
> Is there another way I should specify the User model to the 
> ticket_controller? perhaps model :user, :ticket, :note when I know tickets 
> have notes and belong to a user?
> 
> --
> Craig Beck
> http://blog.rebelplatoon.com
> http://luckybonza.com
> AIM: Kreiggers
> 
> 
> 
> _______________________________________________
> Rails mailing list
> Rails-1W37MKcQCpIf0INCOvqR/iCwEArCW2h5@public.gmane.org
> http://lists.rubyonrails.org/mailman/listinfo/rails
> 
> 
> 

-- 
Jordan Brock
Spin Technologies
www.spintech.com.au <http://www.spintech.com.au>


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Rails - May 2005 - associations basics

associations basics

Re: associations basics

Re: associations basics

Re: associations basics

Re: associations basics

Re: associations basics

Re: associations basics

Re: associations basics