Rails - Feb 2006 - How to set a relationship with a value from a selection list

I realize this is probably a very basic problem but I''m developing my 
first rails app and running into this problem.

I''m trying to write a photoblog application. I have a photo table and
an
album table. Photo has a to-one relationship to Album. Photo.album_id => 
Album.id

In my view for photo I have a selection list that''s populated with all 
the available albums.
<%= select("post", "album_id", Album.find_all.collect
{|a| [a.name,
a.id]}, {:include_blank => true}) %>

This work in so much as I can see the albums being listed in the 
selection list.

Then in my photo_controller I''m trying to set the relationship when the
photo is saved in a method called ''create''

def create
  @photo = Photo.new(params[:photo])
  @photo_file = PhotoFile.new(params[:photo_file])
  @photo.photo_file = @photo_file
  @photo.album = @post.album_id
  @photo.blog_user_id = 1
  if @photo.save!
    flash[:notice] = ''Photo was successfully created.''
    redirect_to :action => ''list''
  else
    render :action => ''new''
  end
end

When I click save I get the following error...

NoMethodError in Photo#create

You have a nil object when you didn''t expect it!
The error occured while evaluating nil.album_id

I''ve looked through this forum and read numerous similar problems, and 
from what I can tell I''m doing the right thing. Can someone tell me 
where I''m being thick.

-Matt

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On Thu, Feb 23, 2006 at 02:28:22PM +0100, Matthew Oliver
wrote:
> 
> I''m trying to write a photoblog application. I have a photo table
and an
> album table. Photo has a to-one relationship to Album. Photo.album_id =>
> Album.id
> 
> In my view for photo I have a selection list that''s populated with
all
> the available albums.
> <%= select("post", "album_id",
Album.find_all.collect {|a| [a.name,
> a.id]}, {:include_blank => true}) %>
s/post/photo/
> This work in so much as I can see the albums being listed in the 
> selection list.
> 
> Then in my photo_controller I''m trying to set the relationship
when the
> photo is saved in a method called ''create''
> 
> def create
>   @photo = Photo.new(params[:photo])
>   @photo_file = PhotoFile.new(params[:photo_file])
>   @photo.photo_file = @photo_file
>   @photo.album = @post.album_id
Remove this line because the hash params[:photo] will contain
the album_id.
>   @photo.blog_user_id = 1
>   if @photo.save!
>     flash[:notice] = ''Photo was successfully created.''
>     redirect_to :action => ''list''
>   else
>     render :action => ''new''
>   end
> end
FWIW I''m new to rails so I could easily be way wrong with my
suggestion. :)

-steve

>>   @photo.album = @post.album_id
> Remove this line because the hash params[:photo] will contain
> the album_id.
> 
>>   @photo.blog_user_id = 1
>>   if @photo.save!
>>     flash[:notice] = ''Photo was successfully
created.''
>>     redirect_to :action => ''list''
>>   else
>>     render :action => ''new''
>>   end
>> end
> 
> FWIW I''m new to rails so I could easily be way wrong with my
> suggestion. :)
> 
> -steve
Hi Steve

If I simply remove that line I get a forien key restraint error.

Mysql::Error: #23000Cannot add or update a child row: a foreign key 
constraint fails (`photoblog_development/photos`, CONSTRAINT 
`photos_ibfk_1` FOREIGN KEY (`album_id`) REFERENCES `albums` (`id`)): 
INSERT INTO photos (`lens`, `mounting`, `title`, `album_id`, 
`photo_description`, `camera`, `iso`, `shutter`, `blog_user_id`, 
`camera_mode`, `added_on`, `shot_on`, `aperture`, `flash`)
VALUES('''',
'''', '''', 0, '''',
'''', '''', '''', 1,
'''', NULL, NULL, '''', '''')

How do I go about setting this relationship?

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>  @photo.album = @post.album_id
>You have a nil object when you didn''t expect it!
>The error occured while evaluating nil.album_id
You use @post, but it''s not defined anywhere. That looks like
what''s
causing the nomethod error.



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On Thursday, February 23, 2006, at 3:14 PM, Andrew Otwell
wrote:
>
>>  @photo.album = @post.album_id
>
>>You have a nil object when you didn''t expect it!
>>The error occured while evaluating nil.album_id
>
>You use @post, but it''s not defined anywhere. That looks like
what''s
>causing the nomethod error.
Whoops, I meant to write: "That looks like what''s causing the _nil
object_ error."



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On Thu, Feb 23, 2006 at 04:04:33PM +0100, Matthew Oliver
wrote:
> 
> If I simply remove that line I get a forien key restraint error.
> 
> Mysql::Error: #23000Cannot add or update a child row: a foreign key 
> constraint fails (`photoblog_development/photos`, CONSTRAINT 
> `photos_ibfk_1` FOREIGN KEY (`album_id`) REFERENCES `albums` (`id`)): 
> INSERT INTO photos (`lens`, `mounting`, `title`, `album_id`, 
> `photo_description`, `camera`, `iso`, `shutter`, `blog_user_id`, 
> `camera_mode`, `added_on`, `shot_on`, `aperture`, `flash`)
VALUES('''',
> '''', '''', 0, '''',
'''', '''', '''', 1,
'''', NULL, NULL, '''', '''')
> 
> How do I go about setting this relationship?
You need to remove the line mentioned as well as make the other
change (post -> photo) in the call to the select method in your
view.  If you don''t then the album_id doesn''t get stuffed in
the
params[:photo] hash which is what is causing the error above.

As it originally stood the album_id could only be obtained using
params[:post][:album_id].  Putting it in the photo attributes hash
means it is supplied to Photo.new in the following line of your
code:

@photo = Photo.new(params[:photo])

This mitigates the need to later have to resort to this:

@photo.album_id = params[:post][:album_id];

-steve

Andrew Otwell wrote:
> On Thursday, February 23, 2006, at 3:14 PM, Andrew Otwell wrote:
>>
>>>  @photo.album = @post.album_id
>>
>>>You have a nil object when you didn''t expect it!
>>>The error occured while evaluating nil.album_id
>>
>>You use @post, but it''s not defined anywhere. That looks like
what''s
>>causing the nomethod error.
> 
> Whoops, I meant to write: "That looks like what''s causing the
_nil
> object_ error."
Ahhhh I see...
So using the variable name post in the select statement isn''t enough?

<%= select("post", "album_id", Album.find_all.collect
{|a| [a.name,
a.id]}, {:include_blank => true}) %>

I thought calling it post here would mean I could reference in my 
controllor as such. I''m still lost as to what I should do? When I try
to
save the new photo I get an exception page that shows me the information 
from the request... in that information I see the album 
"post"=>{"album_id"=>"1"}} and it''s
pointing at the correct id and
everything I just don''t know how to reference that request object in my
controllor to set the relationship!?! frustrating!

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Awesome! It worked!
Thank you so much Steve.

-M

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