Rails 3.1 :has_many, :through complex ordering - ruby-on-rails

Question

I have an orders model with line_items and vendors. When displaying an order, I want to group line_items by vendors.
class LineItem < ActiveRecord::Base
belongs_to :order
belongs_to :vendor
end
class Order < ActiveRecord::Base
has_many :line_items
has_many :vendors, :through => :line_items
end
class Vendor < ActiveRecord::Base
has_many :line_items
end
I want to display a sorted list of vendors and line items:
You have placed an order for the following items:
Vendor 1
Line item 1
Line item 2
Line item 3
Vendor 2
Line Item 4
Line Item 5
...
My current thought is
order.vendors.each do |a_vendor|
a_vendor.name
!!?? AND THEN WHAT GOES HERE ??!!
end
please help. I can't figure this out. maybe this could be done by sorting?
If the order only has one vendor, then I only want to show the one vendor.

Answer 1

How about this:
<% #order.line_items.all.group_by{|i| i.vendor}.each do |vendor, items| %>
<%= content_tag :h2, vendor.id %>
<ul>
<% items.each do |i| %>
<%= content_tag :li, i.id %>
<% end %>
</ul>
<% end %>
[edits]
sort_by(&:vendor) is the same as sort_by{|v| v.vendor}, but the block-style syntax gives you a little more flexibility. For example, you can sort by vendor name in the controller with:
#sorted = #order.line_items.all.group_by(&:vendor).sort_by{|vendor, items| vendor.name}
Then in the view:
<% #sorted.each do |vendor, items| %>
<%= content_tag :h2, vendor.name %>
<ul>
<% items.each do |i| %>
<%= content_tag :li, i.id %>
<% end %>
</ul>
<% end %>

Answer 2

Alternatively, can sort in the model by adding an SQL snippet
to the :order option of the has_many association.
(See: http://api.rubyonrails.org/classes/ActiveRecord/Associations/ClassMethods.html#method-i-has_many)
class Order < ActiveRecord::Base
has_many :line_items, :order => "item_number"
has_many :vendors, :through => :line_items, :order => "name"
end
Then your view is very simple:
<% #order.vendors.each do |vendor| %>
<h3><%= vendor.name %></h3>
<ul>
<% vendor.line_items.where(:order_id=>#order.id).each do |item| %>
<li><%= item.description %></li>
<% end -%>
</ul>
<% end -%>