Creating new instance of dependent model

Question

I am tweaking "getting started" tutorial and trying to create an instance of a dependant model.

My models are Museum and Exhibition (Article and Comment in the tutorial).

The tutorial teaches how to create an instance of Comment when located in the Artcicle#show ERB file. This is achieved by using the following form helper:

<%= form_for([@article, @article.comments.build]) do |f| %>

I guess this form helper allows the form to access the Article Id and therefore allows accurate dependency.

I have managed to do that with my own models Museum and Exhibition.

Though I would like to be able to create an Exhibition instance without being located in the Museum#Show ERB file. But directly inside the Exhibition#New ERB file.

I have realised there was no route initially to do that, then have declared Exhibition as a proper ressource, on top of being dependant to Museum. Here my Routes file now :

resources :exhibitions

resources :museums

resources :museums do
   resources :exhibitions
end

which have created appropriate routes.

Though I am struggling with the Exhibition#New controller and ERB files.

Intuitively I understand I need to pass a list of all museums instances Ids and Names so that the user can choose to which Museum the exhibition belongs to.

But all my attempts to create the form helper have failed so far. My lastattempt was as such :

<%= form_for([@museum, @museum.exhibitions.build]) do |f| %>

<p>

  <%= f.select @museum.id, options_for_select(@museum.name) %>     </p>
....

with the following Exhibition controller bit :

def new
@museum = Museum.all
end

Answer 1

You don't go for a nested form when creating the exibition in this case. Just provide a select tag with option for each museum.

controller:

def new
    @exibition = Exibition.new
end


view:
<%= form_for(@exibition) do |f| %>
    ...
    <%= f.collection_select(:museum_id, Museum.all, :id, :name) %>

Answer 2

For your exhibitions#new which takes the route-path /museums/1/exhibitions/new (as an example), then:

def new
  puts params[:museum_id]
  # => 1

  @museum = Museum.find(params[:museum_id])
  @exhibition = Exhibition.new
end

Since @museum is now a Record object, then you could use the following in your exhibitions/new.html.erb

<%= form_for(@exhibition, url: museum_exhibitions_path(@museum)) do |f| %>

Take note that museum_exhibitions_path(@museum) translates to a path /museums/1/exhibitions in which...

1. if it is a GET request, then it will be handled by controller-method exhibitions#index

2. if it is a POST request, then it will be handled by controller-method exhibitions#create

Now, because form_for automatically uses POST request by default, then exhibitions#create, will be delegated to this route, which is what we wanted.

OR just use

<%= form_for([@museum, @exhibition]) do |f| %>