Question

I’m trying to pick out an instance of a model (“Package”) by its relation to two other models to which it belongs (“Cut” and “Animal”). While there are, say many packages with :cut_id 3 and many with :animal_id 4, there should only be one with both, and I want to pick that one out and display its contents in a table.

I’ve tried the following DIY mess, and it’s not really working. (cutfind is a method I created that I know works for calling out all of the cuts associated with the given animal.)

<% @animal.cutfind.each do |cut| %>
  <tr>
    <td><%= cut.name %></td>
    <td><%= number_to_currency(cut.price) %></td>
    <td><%= cut.package_weight %> lb</td>
        <% @a = Package.where(:animal_id => @animal.id) %>
        <% @pset = @a.where(:cut_id => cut.id) %>
    <% @pset.each do |p| %>
        <td><%= p.original %></td>
        <td><%= p.left %></td>
    <% end %>
  </tr>
<%end%>

Any idea how to do this [better]? Thanks.

Update: I tried this other DIY mess and am getting the same problem (the cells aren’t even being created, which leads me to believe that @pset is empty).

This is in my animal model:

def packagefind
    Package.where(:animal_id => self.id)
end

And then I changed the above like so:

<td><%= cut.package_weight %> lb</td>
        <% @pset = @animal.packagefind.where(:cut_id => cut.id) %>
    <% @pset.each do |p| %>
        <td><%= p.original %></td>
        <td><%= p.left %></td>
    <% end %>

Answer 1

As I’m not able to comment on your post, I take a guess:
You have the folllowing architecture:

Cut -> Package <- Animal

In this, “->” and “<-” are one-to-many relationships so that

class Package < ActiveRecord::Base
  has_many :cuts
  has_many :animals
end

So, you want “the” package, that has Cut with id 3 and Animal id 4.
Did you try:

x = Product.select { |product| product.cuts.include?(Cut.find(3)) }.select{ |product| product.animals.include?(Animal.find(4)) }

?

EDIT: I first suggested to you use

Product.find_by_product_id_and_animal_id() 

which didn’t work but showed the OP the way to do it