Nested wIth existing objects?

Question

I'm attempting to build a form which allows a user to select multiple Labels when creating a new Item, without allowing the user to create new Labels.

Here's how my models are set up:

Item
has_many :item_labels
has_many :labels, :through => :item_labels

ItemLabel
belongs_to :item
belongs_to :label

Label
has_many :item_labels
has_many :items, :through => :item_labels

Any ideas how I could create this sort of relationship within a form without allowing the user to create new labels? (Label creation is only done by the admin.)

Specifically, how should I set up the form in the view, and are there any changes I should make to my models? (accepts_nested_parameters or other directives)

Michael Stalker · Accepted Answer · 2013-11-14 19:43:26Z

1

I don't think you'll need accepts_nested_attributes for this. I haven't tried all this out, so YMMV :)

Here's how you might set up a new item in your controller. I'm setting a @labels instance variable, too, since I'll use that in a collection_select in the view:

# items_controller.rb
class ItemsController < ApplicationController
  def index
    @items = Item.all
  end

  def new
    @item = Item.new
    @labels = Label.all
  end

  def create
    @item = Item.new(params[:item])

    if @item.save
      flash[:info] = 'Item successfully created.'
      redirect_to items_path
    else
      @labels = Label.all
      render :new
    end
  end
end

Assuming your Label model has a name attribute, your form could look like this:

# new.html.erb
<%= form_form @item do |f| %>
  <!-- Other item fields go here -->

  <%= f.label :label_ids %>
  <%= f.collection_select :label_ids, @labels, :id, :name, {}, multiple: true %>

  <%= f.submit %>
<% end %>

You can read some more about collection_select to learn a bit more about that.

answered Nov 14, 2013 at 19:43

Michael Stalker

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Michael Stalker Over a year ago

@Rob glad to hear it!

David Grayson · Accepted Answer · 2013-11-14 19:19:46Z

1

Well, what part are you stuck on?

For the UI side, you might consider the chosen-rails gem:

https://github.com/tsechingho/chosen-rails

It lets users just start typing the name of an item and it helps them auto-complete it, similar to what happens when you select recipients for a message in Facebook. I think you should be able to use it to let the user select multiple labels.

answered Nov 14, 2013 at 19:19

David Grayson

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1 Comment

Rob Over a year ago

I know if I'm creating new objects I would do something like f.fields_for :labels do... Then edit the model to accept_nested_attributes. Is it done similarly with existing objects? I can't seem to find this anywhere on google

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