Rails 4 - Using collection_select to get an array of ids for an Intermediate Table with Nested Attributes

Question

I want to rewrite manual logic for updating a table to use nested attributes while using a third table to select multiple id values. This is my first time attempting this.

I have a MediaLibrary model. I have a PageTitle model which contains names. I have a MediaPage model which contains the id fields for MediaLibrary and PageTitle. I want to populate MediaPage using nested attributes. I want to create a collection_select for PageTitle which has the values that populate page_title_id MediaPage.

Here are my model definitions.

media_library.rb

has_many :media_pages, dependent: :destroy
accepts_nested_attributes_for :media_pages, allow_destroy: true  

media_page.rb

belongs_to :media_library

validates :media_library_id, presence: true  
validates :page_title_id, presence: true 

page_title.rb

has_many :media_pages

My original view code when I was manually collecting the values is below.

<%= fields_for :media_pages do |media_page| %>
  <%= media_page.label :media_page, "Page Titles" %><%= media_page.collection_select(:page_title_id, PageTitle.order("name"), :id, :name, {}, {multiple: true}) %>
<% end %>

Here is my current view:

<%= f.label :media_pages, "Page Titles" %>
<%= f.fields_for :media_pages do |media_page| %>
  <%= media_page.collection_select(:page_title_id, PageTitle.order("name"), :id, :name, {}, {multiple: true}) %>
<% end %>

If I have more than one MediaPage row the view will show a collection_select list for each row. For example if I have two MediaPage rows I will see one collection_select list with the PageTitle name for the first record highlighted and a second collection_select list with the PageTitle name for the second record highlighted. As you can see the only things I changed from my first fields_for statement and the second one is (1) moving the label outside of the fields_for and (2) adding f.

I attempted something similar in Rails 3 Rails 3.2.13 - Delete Entry From Nested Attributes. When I attempted this in Rails 3 the collection_select only displayed one list with multiple rows highlighted. Since there was an issue with a blank array entry I decided to continue doing the manual process of updating the intermediate table.

What I want is to have one collection_select list displayed on my view where multiple PageTitle ids can be selected and populate the MediaPage table using nested attributes. If rows exist I want the corresponding PageTitle rows to be highlighted.

I have been trying to solve this for a long while. Through my research I have not found any examples where nested attributes were populated using a separate table.

Any help would be appreciated.

Answer 1

After doing more checking I was able to find a solution. I implemented something similar to what I read on Rails has_many :through and collection_select with multiple.

media_library.rb

has_many :page_titles, through: :media_pages
has_many :media_pages, dependent: :destroy
accepts_nested_attributes_for :media_pages, allow_destroy: true

media_page.rb

belongs_to :media_library  
belongs_to :page_title

page_title.rb

has_many :media_pages, dependent: :destroy

I replaced the fields_for with the following collection_select statement.

<%= collection_select(:media_library, :page_title_ids, PageTitle.order("name"), :id, :name, {:selected => @media_library.page_title_ids, include_hidden: false}, {:multiple => true}) %>

Now I have the rows in the drop down list selected with the page_title_ids from MediaPage. I am manually deleting and adding the MediaPage rows from params[:media_library][:page_title_ids].