Nested forms creates empty instances - ruby-on-rails

Question

I have a Post and a MaterielLink models.
A post has_many materiel_links, and accepts_nested_attributes_for :materiel_links
I use the gem cocoon to create a nested form: on the post form, I want to be able to add links that will be created on submit of the form.
post/new.html.erb:
<%= simple_form_for #post, :html => { :id => "post_form", "data-post-id" => #post.id } do |f| %>
<%= f.simple_fields_for :materiel_links do |materiel_link| %>
<%= render 'materiel_link_fields', f: materiel_link %>
<% end %>
<%= link_to_add_association 'Ajouter', f, :materiel_links%>
<% end %>
_materiel_link_fields.html.erb:
<%= f.fields_for :materiel_links do |materiel_link| %>
<%= materiel_link.text_field :name %>
<%= materiel_link.text_field :link %>
<% end %>
In my post controller:
def update
#materiel_links = #post.materiel_links.build(post_params[:materiel_links_attributes]
if #post.update!(post_params)
session[:current_draft_post_id] = nil
redirect_to post_path(#post)
else
render :new
end
end
I am here in the update action since, for reasons specific to my rails app, the post is created when the posts/new page is rendered (It is created empty, and the user just updates it instead of actually creating it). So the post already exists, but not the materiel_links that I have to create in the update action.
And the params:
def post_params
params.require(:post).permit(:title, materiel_links_attributes: [:name,:link] )
end
I added a raise in the update action, and what is stange is that I can find the link/name for each materiel_link I've added when I type params but with a number before each couple:
>> params
{"utf8"=>"✓", "_method"=>"patch", "authenticity_token"=>"wqzWfaAcwrOOdxViYBO5HaV2bwsNsf5HsvDFEbBYapkOMAPXOJR7oT4zQHbc/hTW8T9a+iH5NRl1WUApxrIjkA==", "post"=>{"title"=>"my title", "materiel_links_attributes"=>{"1459431927732"=>{"materiel_links"=>{"name"=>"mon Lien 1", "link"=>"htttp1"}}, "1459431933881"=>{"materiel_links"=>{"name"=>" Mon lien 2", "link"=>"htttp2"}}}}, "controller"=>"posts", "action"=>"update", "id"=>"1250"}
But nothing in the materiel_links hashes when I type post_params:
>> post_params
=> {"title"=>"my title","materiel_links_attributes"=>{"1459431927732"=>{}, "1459431933881"=>{}}}
The instances of MaterielLink are created, but they are empty: they don't save the link/name.
Where did I go wrong ?

Answer 1

My guess is that because in your update action you used .build before .update, it somehow conflicted with .update because the materiel_links values are passed there once again. You do not need to build in update action anymore; but only in edit action, because the materiel_links will be automatically created/updated when .update(post_params) is called, as post_params already include materiel_links values. Try
def update
if #post.update!(post_params)
#materiel_links = #post.materiel_links
session[:current_draft_post_id] = nil
redirect_to post_path(#post)
else
render :new
end
end
You'd also need whitelist the ID of materiel_link in strong params, so that these materiel_links in the form can be updated (ID not needed to be whitelisted if just create, and no update). You might also want to allow destroy. Update into the following:
def post_params
params.require(:post).permit(:title, materiel_links_attributes: [:id, :name, :link, :_destroy] )
end
# post.rb
accepts_nested_attributes_for :materiel_links, allow_destroy: true