Question

I setup a has_many through association with my models and I am trying to create a form where I can add multiple genres to a submitted song. I am using the collection_select helper for this. Here are snippets on how my code is setup.

Song Model

has_many :song_genres
has_many :genres, :through => :song_genres

Genre Model

has_many :song_genres
has_many :songs, :through => :song_genres

Song Genre Model

belongs_to :song
belongs_to :genre

Then in my new.html.erb
I have this

collection_select :song, :genres, Genre.all, :id, :name, {:selected => 1}, {:multiple => true}

When I submit the form I get a

Can't mass-assign protected attributes: genres

error

I know I’m missing something big here. Can someone help me out on how to properly set this up?

Thanks!

Answer 1

Try this way:

collection_select :song, :genre_id, Genre.all, :id, :name, {:selected => 1}, {:multiple => true}

As stated in the Rails guide:
“If you are using select (or similar helpers such as collection_select, select_tag) to set a belongs_to association you must pass the name of the foreign key (in the example above city_id), not the name of association itself.”