Nested attributes with belongs_to

Rails
1

Here is my model looks like:-
Model: Movie
has_many :songs

Model: Song
belongs_to :movie

I have a songs/new form which contains song name and movie name input
field.
If movie name does not exist it should create a new one else it should
use
already existing one. So this I will come to know only after user enter
in
movie name field.

Can I achieve this using nested attributes of rails 3?

Note: I can able to implement the same in has_many association but not
in
this case.

Thanks!
Butu

2

Butu,

You should look at before_create in ActiveRecord. I think it would be
better if you put on in your Song Model that calls private function to
check whether the passed in Movie name exists or not. If it doesn’t,
create it and if it does exist do nothing.

Thanks,

B.

3

Thanks Bryan for your reply.

For first part of my problem, I am able to figure out the nested
attributes
with belongs_to.

For second part, I am looking for Rails way solution to my problem.

Using nested attribute. I can able to create Movie if it does not exist.
And
able to associate it with song model (movie_id populated correctly)
work
really good by rails way. I want this behavior.

But when movie already exist. I want to associate that movie id with
the
new song to be created using accepts_nested_attributes_for.
*
*
Thanks!
Butu

4

On Wed, Feb 23, 2011 at 2:54 PM, Butu [email protected] wrote:

But when movie already exist. I want to associate that movie id with the
new song to be created using accepts_nested_attributes_for.
*
*

you can’t. accepts_nested_attributes_for doesn’t work on belongs_to
attribute.

check whether the passed in Movie name exists or not. If it doesn’t,

Model: Song
in
[email protected].
[email protected].
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk?hl=en.

–

5

Hello Jim,

Thanks for your reply.

I can able to do accepts_nested_attributes with belongs_to

@song.build_movie

use this either in action or before the form and use fields_for. This
will
create the new movie record and insert movie_id in song model as well.

6

You don’t need to use nested attributes for that. You can achieve the
same result with a pretty simple virtual attribute:

class Song < ActiveRecord::Base
belongs_to :movie

def movie_name=(name)
@movie_name = name
self.movie = Movie.find_or_initialize_by_name(name)
end

def movie_name
@movie_name
end
end

And then on your form:

= form_for @song do |form|
= form.text_field :movie_name

7

Reu, thanks a lot!! this is exactly what I want.

Facing one problem when I am using accepts_nested_attributes_for and
has_many. This is working in rails way and able to insert record into
songs,
people and people_song table correctly. But again I want to use similar
logic find and initilize. But in that case I may need to insert into
people_song table manually. Any thoughts on this?

Thanks!
Butu