Populating a self join table in Rails 4 - ruby-on-rails

Question

I have a product table and a related product table, related works one way:
Product(id: int, name: string)
RelatedProduct(id: int, product1: int, product2: int)
With the following models:
class Product < ActiveRecord::Base
validates :name, :uniqueness => true, :presence => true
has_many :relations, :class_name => "RelatedProducts", :foreign_key => :product1, inverse_of: :source
has_many :related_products, through: :relations, :source => :destination
end
class RelatedProducts < ActiveRecord::Base
belongs_to :source, :class_name => "Product", inverse_of: :relations
belongs_to :destination, :foreign_key => :product2, :class_name => "Product"
end
This works if I prepopulate the RelatedProducts table, the show view will correctly display all the related products. What I cannot figure out is how do to populate RelatedProducts from the html?
<%= form_for(#product) do |f| %>
<div class="field">
<%= f.label :name %>
<%= f.text_field :name %>
</div>
<div class="related-products field">
<h3>Related Products</h3>
<%= f.collection_check_boxes :related_products, Product.where.not(id: #product.id), :self, :name %>
</div>
<div class="actions">
<%= f.submit 'Update Products' %>
</div>
<% end %>
The strong parameters are defined as:
params.require(:product).permit(:name, related_products: [:id, :name])

Answer 1

My solution was to make the view use the ids and then submit them
<div class="related-products field">
<h3>Related Products</h3>
<%= f.collection_check_boxes :related_products, Product.where.not(id: #product.id), :id, :name %>
</div>
I then coupled this with a function in the model to convert the id list to a list of products
def related_products_list=(ids)
self.related_products = ids.reject(&:empty?).collect { |id| Product.find(id) }
end
This worked for submitting but the checkboxes would not be pre checked on edits. This was because the model talks about products but the view has a list of ids so would not spot matches. The solution I used was to manually loop through the collection to create the checkboxes instead of using collection_check_boxes.
<% Product.where.not(id: #product.id).each do |p| %>
<%= check_box_tag 'product[related_products][]', p.id, #product.is_related_to?(p), id: "product_related_products_" + p.id.to_s %>
<%= label_tag "product_related_products_" + p.id.to_s, p.name %>
<% end %>