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Jon

2008-Sep-26 04:53 UTC

has_many / belongs_to associations

I have two models, Review and Album.

Album has many reviews, and Review belongs to Album as seen below in
their respective model files.

class Review < ActiveRecord::Base
	belongs_to :album
end

class Album < ActiveRecord::Base
	has_many :reviews
end

I then added a form to submit reviews for an album:

<% form_for @review do |f| %>
	<textarea cols="40" id="review_productReview"
name="review[productReview]"
rows="10"></textarea><br>

	<input type=''hidden'' id="review_product"
name="review[product]"
value=''<%= @album.title%>'' >
	<input type=''hidden'' id="review_productCreator"
name="review[productCreator]" value=''<%=
@album.artist%>'' >
	<input name="commit" type="submit" value="Submit
Review" />
<% end %>

In my controller I have :

class ReviewsController < ApplicationController

  def create
  	@review=Review.new(params[:review])
  	@review.album=@album
  	@review.save
  	redirect_to ''/inventory''
  end

end

i''m not sure that @review.album=@album is the correct syntax, but even
at the command line when I instantiate an object of type Review and do
Review.album.title="GoldDigger", it says that album is an undefined
method.  The only thing I can think of is that I am missing something
when I set up the associations.
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Pokkai Dokkai

2008-Sep-26 06:08 UTC

head link

Re: has_many / belongs_to associations

Jon wrote:
>   def create
>     @review=Review.new(params[:review])
>     @review.album=@albumthats correct syntax (if @album is a object of Album model)

> 
> i''m not sure that @review.album=@album is the correct syntax, but
even
> at the command line when I instantiate an object of type Review and do
> Review.album.title="GoldDigger", it says that album is an
undefined
here ''Review'' is not a model object ,thats a model class

and always you can''t get any association with any model class (except
if
you write your own code inside of that model class)

first
@review=Review.find(id)
unless @review.album
@review.album=Album.find(id)
end
@review.album.title="GoldDigger"
> method.  The only thing I can think of is that I am missing something
> when I set up the associations.
-- 
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Frederick Cheung

2008-Sep-26 07:06 UTC

head link

Re: has_many / belongs_to associations

On Sep 26, 5:53 am, Jon <jonli...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:> class ReviewsController < ApplicationController
>
>   def create
>         @review=Review.new(params[:review])
>         @review.album=@album
>         @review.save
>         redirect_to ''/inventory''
>   end
The problem you have is that @album is nil, because you haven''t set it
to anything. It may have been set when you rendered the form, but that
was a different instance of the controller (quite possibly in a
different process or even server). You need to have whatever parameter
in the form you need to be able to retrieve that album, (eg a
hidden_field)

Fred>
> end
>
> i''m not sure that @review.album=@album is the correct syntax, but
even
> at the command line when I instantiate an object of type Review and do
> Review.album.title="GoldDigger", it says that album is an
undefined
> method.  The only thing I can think of is that I am missing something
> when I set up the associations.--~--~---------~--~----~------------~-------~--~----~
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Jon Liu

2008-Sep-26 14:18 UTC

head link

Re: has_many / belongs_to associations

I tried manually defining @album like so

     id=1
     @review=Review.new(params[:review])
     @review.album=Album.find(id)
     @review.save

Because of this, I don''t think it''s that @album was not
defined.  Also as I
brought up before, and I think this is key in showing their is something
fundamentally wrong in my set up, the association doesn''t even work at
the
command line.

Ex:
a=Album.find(1)
r=Review.new
r.album=a

This yields an error that says "NoMethodError: undefined method
''album='' for
#<Review:......"

Any insight?



On Fri, Sep 26, 2008 at 12:06 AM, Frederick Cheung <
frederick.cheung-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
>
>
>
> On Sep 26, 5:53 am, Jon
<jonli...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> > class ReviewsController < ApplicationController
> >
> >   def create
> >         @review=Review.new(params[:review])
> >         @review.album=@album
> >         @review.save
> >         redirect_to ''/inventory''
> >   end
>
> The problem you have is that @album is nil, because you haven''t
set it
> to anything. It may have been set when you rendered the form, but that
> was a different instance of the controller (quite possibly in a
> different process or even server). You need to have whatever parameter
> in the form you need to be able to retrieve that album, (eg a
> hidden_field)
>
> Fred
> >
> > end
> >
> > i''m not sure that @review.album=@album is the correct syntax,
but even
> > at the command line when I instantiate an object of type Review and do
> > Review.album.title="GoldDigger", it says that album is an
undefined
> > method.  The only thing I can think of is that I am missing something
> > when I set up the associations.
> >
>
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Frederick Cheung

2008-Sep-26 14:27 UTC

head link

Re: has_many / belongs_to associations

On Sep 26, 3:18 pm, "Jon Liu"
<jonli...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:> I tried manually defining @album like so
>
>      id=1
>      @review=Review.new(params[:review])
>      -dnBBAB2HhyXg6WpnEXGJrQ@public.gmane.org=Album.find(id)
>      -zwA3+X6BIaLfhZSSa7DgLw@public.gmane.org
>
> Because of this, I don''t think it''s that @album was not
defined.  Also as I
> brought up before, and I think this is key in showing their is something
> fundamentally wrong in my set up, the association doesn''t even
work at the
> command line.
>
> Ex:
> a=Album.find(1)
> r=Review.new
> r.album=a
>
> This yields an error that says "NoMethodError: undefined method
''album='' for
> #<Review:......"
>
> Any insight?
>
Well the full stacktrace is sometimes helpful. Just to be sure, your
reviews table does have an album_id column ?

Fred
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Jon Liu

2008-Sep-26 16:38 UTC

head link

Re: has_many / belongs_to associations

how do you view the stacktrace?  I thin this is the solution to my
problem...only now migrations is acting funny with me...

On Fri, Sep 26, 2008 at 7:27 AM, Frederick Cheung <
frederick.cheung-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
>
>
>
> On Sep 26, 3:18 pm, "Jon Liu"
<jonli...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> > I tried manually defining @album like so
> >
> >      id=1
> >      @review=Review.new(params[:review])
> >      @review.album=Album.find(id)
> >      @review.save
> >
> > Because of this, I don''t think it''s that @album was
not defined.  Also as
> I
> > brought up before, and I think this is key in showing their is
something
> > fundamentally wrong in my set up, the association doesn''t
even work at
> the
> > command line.
> >
> > Ex:
> > a=Album.find(1)
> > r=Review.new
> > r.album=a
> >
> > This yields an error that says "NoMethodError: undefined method
''album=''
> for
> > #<Review:......"
> >
> > Any insight?
> >
>
> Well the full stacktrace is sometimes helpful. Just to be sure, your
> reviews table does have an album_id column ?
>
> Fred
> >
>
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torm3nt

2008-Oct-13 04:08 UTC

head link

Re: has_many / belongs_to associations

I''m only guessing here, but I''m thinking maybe that your issue
is
centred around the way rails automagically creates the setter and
getter methods for associations. From what I''m seeing, I''m
guessing
that has_many creates attr_writer methods whereas belongs_to only
creates attr_reader methods. What this means is, album= will not be an
accessible method, so trying to set the album within a "child"
association isn''t possible (nor should it be). What you need to do is
simply set the album_id. I''ve never tried to create associative data
the way you are, so I can''t say for sure this is the issue, but I
think it''s possible. You generally don''t create relationships
via
belongs_to.

Going the other way, you shouldn''t have any problems though.

Ie.

@album = Album.new( your params )
@album.reviews = [ Review.new( review1params ),
Review.new( review2.params ) ]
@album.save

.etc.etc.

Hope that helps.


Kirk "Torm3nt" Bushell


On Sep 27, 3:38 am, "Jon Liu"
<jonli...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:> how do you view the stacktrace?  I thin this is the solution to my
> problem...only now migrations is acting funny with me...
>
> On Fri, Sep 26, 2008 at 7:27 AM, Frederick Cheung <
>
> frederick.che...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
>
> > On Sep 26, 3:18 pm, "Jon Liu"
<jonli...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> > > I tried manually defining @album like so
>
> > >      id=1
> > >      @review=Review.new(params[:review])
> > >      @review.album=Album.find(id)
> > >      @review.save
>
> > > Because of this, I don''t think it''s that @album
was not defined.  Also as
> > I
> > > brought up before, and I think this is key in showing their is
something
> > > fundamentally wrong in my set up, the association
doesn''t even work at
> > the
> > > command line.
>
> > > Ex:
> > > a=Album.find(1)
> > > r=Review.new
> > > r.album=a
>
> > > This yields an error that says "NoMethodError: undefined
method ''album=''
> > for
> > > #<Review:......"
>
> > > Any insight?
>
> > Well the full stacktrace is sometimes helpful. Just to be sure, your
> > reviews table does have an album_id column ?
>
> > Fred
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Pardee, Roy

2008-Oct-13 14:17 UTC

head link

Re: has_many / belongs_to associations

Nah, you can set a parent from a child.  Dig it:

  >> hh = Album.new(:title => "Houses of the Holy", :artist
=> "Led Zepplin")
  => #<Album id: nil, title: "Houses of the Holy", artist:
"Led Zepplin", release_date: nil, created_at: nil, updated_at: nil>
  >> hhr = Review.new(:title => "Led Zep''s new album
rocks", :review_body => "Best.  Album.  Ever.")
  => #<Review id: nil, title: "Led Zep''s new album
rocks", review_body: "Best.  Album.  Ever.", album_id: nil,
created_at: nil, updated_at: nil>
  >> hh.save
  => true
  >> hhr.save
  => true
  >> hhr.album = hh
  => #<Album id: 1, title: "Houses of the Holy", artist:
"Led Zepplin", release_date: nil, created_at: "2008-10-13
07:13:04", updated_at: "2008-10-13 07:13:04">
  >> hhr.save
  => true
  >>

-Roy

-----Original Message-----
From: rubyonrails-talk-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
[mailto:rubyonrails-talk@googlegroups.com] On Behalf Of torm3nt
Sent: Sunday, October 12, 2008 9:08 PM
To: Ruby on Rails: Talk
Subject: [Rails] Re: has_many / belongs_to associations


I''m only guessing here, but I''m thinking maybe that your issue
is centred around the way rails automagically creates the setter and getter
methods for associations. From what I''m seeing, I''m guessing
that has_many creates attr_writer methods whereas belongs_to only creates
attr_reader methods. What this means is, album= will not be an accessible
method, so trying to set the album within a "child"
association isn''t possible (nor should it be). What you need to do is
simply set the album_id. I''ve never tried to create associative data
the way you are, so I can''t say for sure this is the issue, but I think
it''s possible. You generally don''t create relationships via
belongs_to.

Going the other way, you shouldn''t have any problems though.

Ie.

@album = Album.new( your params )
@album.reviews = [ Review.new( review1params ), Review.new( review2.params ) ]
@album.save

.etc.etc.

Hope that helps.


Kirk "Torm3nt" Bushell


On Sep 27, 3:38 am, "Jon Liu"
<jonli...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:> how do you view the stacktrace?  I thin this is the solution to my
> problem...only now migrations is acting funny with me...
>
> On Fri, Sep 26, 2008 at 7:27 AM, Frederick Cheung <
>
> frederick.che...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
>
> > On Sep 26, 3:18 pm, "Jon Liu"
<jonli...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> > > I tried manually defining @album like so
>
> > >      id=1
> > >      @review=Review.new(params[:review])
> > >      @review.album=Album.find(id)
> > >      @review.save
>
> > > Because of this, I don''t think it''s that @album
was not defined.
> > > Also as
> > I
> > > brought up before, and I think this is key in showing their is
> > > something fundamentally wrong in my set up, the association
> > > doesn''t even work at
> > the
> > > command line.
>
> > > Ex:
> > > a=Album.find(1)
> > > r=Review.new
> > > r.album=a
>
> > > This yields an error that says "NoMethodError: undefined
method ''album=''
> > for
> > > #<Review:......"
>
> > > Any insight?
>
> > Well the full stacktrace is sometimes helpful. Just to be sure, your
> > reviews table does have an album_id column ?
>
> > Fred


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Rails - Sep 2008 - has_many / belongs_to associations

has_many / belongs_to associations

Re: has_many / belongs_to associations

Re: has_many / belongs_to associations

Re: has_many / belongs_to associations

Re: has_many / belongs_to associations

Re: has_many / belongs_to associations

Re: has_many / belongs_to associations

Re: has_many / belongs_to associations