dm-0.10-order-option.rb

class PurchaseOrder
  include DataMapper::Resource
  storage_names[:default] = ...

  property :id, Serial, :field => 'purchaseorderindex'
  ...
  property :closed_date, Date, :field => 'closeddate'
  ...
  
  has n, :items, :model => 'PurchaseOrderLineItem', :child_key => [:po_id, Integer], :deleted => false
end

class PurchaseOrderLineItem
  include DataMapper::Resource

  before :destroy, :check_receiving
  storage_names[:default] = 'poitem'
  
  property :id, Serial, :field => 'poitemindex'
  property :cb3_id, Integer, :field => 'codebook3index'
  property :po_id, Integer, :field => 'purchaseorderindex'
  ...
  property :deleted, Boolean, :default => false, :field => 'deleteflag'
  
  belongs_to :po, :model => 'PurchaseOrder', :child_key => [:po_id, Integer]

  ...
end

I want to get the lasted *purchased* PurchaseOrderLineItem which has the cb3_id = xxxx.

1. purchased - the closed purchase order
2. latest -    has to be ordered by purchaseOrder closed_date.desc
3. I want the line item(not the order) which is specified by cb3_id

Here is the query(which is simplified):
PurchaseOrder.first(:completed => 'yes', :order => [:closed_date.desc], 'items.cb3_id' => 17633333).items.first(:cb3_id => 1763333)

I have to do the second cb3_id against the items, because that order might have several line items.