Question

I am developing a program for a warehousing/shipping company with the following Data relationships. The skinny regarding the relationships below is that the warehouse receives raw materials(product) from various carriers(clients) and stores them until they are needed to be shipped to the manufacturing plant. When a shipment leaves the warehouse, the manufacturing facility must know which company each raw material originated from. Take a look at the following ERD.

EDIT: My relationships in text form.

shipment.rb

has_many :product_shipments, :dependent => :destroy
has_many :products, :through => :product_shipments

product_shipment.rb

belongs_to :product
belongs_to :shipment

product.rb

has_many :product_shipments
has_many :shipments, :through => :product_shipments, :dependent => :destroy
belongs_to :client

client.rb

  has_many :products, :dependent => :destroy

I’m having trouble generating the queries in a manner that’s formatted the way the requirements demand. The shipment report takes a date and must iterate through each client and list the products shipped to the manufacturing facility on that given date. It needs to be generated dynamically and formatted like the following.

Shipment Date: 2013-01-01

Client: 12 Name: ACME Widget Co

Product Name | Product Code | Qty Shipped
_________________________________________ 
nuts & bolts |      gj-3423 |          25
steel sheet  |      4g-2394 |          10
dc Motor     |      cj-c213 |           4


Client: 14 Name: Blah Blah, Inc

Product Name | Product Code | Qty Shipped
_________________________________________ 
spacers      |      gj-3423 |          15
epoxy        |      4g-2394 |          10
dc Motor     |      24-gj19 |           6

Client: 15 Name: Sample Co, Inc

Product Name | Product Code | Qty Shipped
_________________________________________ 
hot roll 48  |      cg-3423 |          15
welding wir  |      4g-2394 |          10
dc Motor     |      c2-1241 |           6
.
.
.
.

The problem is generating Queries using ActiveRecord. It’s easy to grab the shipments and products for a given date for ex below. It is not easy to grab the original client that the raw material originated from, then iterate through shipments to the manufacturing facility for that client dynamically.

UPDATE: I am now able to group clients and shipments like above. Now I need to exclude clients where they DON’T have a shipment on the date specified. The below, although somewhat correct, still gives the dreaded O(n) query. Here is what I have.

@clients = Client.includes(:products => :shipments)
@clients.each do |c|
  puts c.name
  c.products.each do |p|
    p.shipments.where("ship_date like '#{@ship_date.strftime("%Y-%m-%d")}%'").each do |s|
      s.product_shipments.joins(:product).each do |ps|
        puts s.bill_of_lading + " " + ps.product_id.to_s + " " + ps.product.product_name.to_s + " " + ps.product.product_code + " " +ps.qty_shipped.to_s + " " + s.ship_date.to_s
        end
    end
  end
end

My issue is how do I organize the query to start with clients and then list products shipped on ‘2012-06-30. The query gets wacko from that perspective. I am unsure how to generate a query with active record when the relationship is that far removed.

Answer 1

Here’s how I did it. Maybe not the best way to do it but it’s close. Thanks for @charlysisto for sending me in the right direction with easy loading the relationships. I still get a O(n) on the join query for the lookup table, but could be worse. Any refinements please comment so I can improve the answer.

@clients = Client.order("clients.id ASC").includes(:products => :shipments).where("shipments.ship_date like '#{ship_date}'")
@clients.each do |c|
  puts c.name
  c.products.each do |p|
    p.shipments.each do |s|
      s.product_shipments.joins(:product).each do |ps|
        puts shipment and products stuff
      end
    end
end