Hi, Ray.
When you are doing things that have a relational algebra feel to them
(joins, etc.), you might want to consider the fns in the clojure.set
namespace. E.g.:
;; convert vectors of records to sets, then:
> (clojure.set/join
(clojure.set/rename items {:id :iid :name :iname}) ; to prevent
overwriting keys in the result
products
{:product :id}) ; 'where items.product = products.id'
=>
#{
{:prices #user.Price{:price 45.99, :tax-rate 21, :currency "EURO"},
:description "Slim Fit White Vest Shirt",
:name "Shirt", :id "P-678",
:iid 3,
:product "P-678",
:quantity 1,
:purchased true,
:iname "Shirt"}
...}
It might look even nicer if you just used regular maps with namespaced keys
instead of records:
(clojure.set/join items products {:item/product :product/id})
Hope that helps,
Leif
On Saturday, December 15, 2012 11:25:59 AM UTC-5, mond wrote:
>
> I have defined these types of records for modelling a simple shopping cart:
>
> ; An item in the cart
> (defrecord Item [id name product quantity purchased])
>
> ; The product that relates to the item in the cart
> (defrecord Product [id name description prices])
>
> ; A price definition
> (defrecord Price [price tax-rate currency])
>
>
> ; Sample items
> (def items [
> (->Item 1 "Brogues" "P-123" 1 true)
> (->Item 2 "Underpants" "P-345" 1 false)
> (->Item 3 "Shirt" "P-678" 1 true)
> ])
>
> ; Sample products
> (def products [
> (->Product "P-123" "Brogues" "Men's Leather Slip on
> Brogues" (->Price 93.00 21 "EURO"))
> (->Product "P-345" "Underpants" "CK Y Fronts" (->Price
> 23.50 21 "EURO"))
> (->Product "P-678" "Shirt" "Slim Fit White Vest Shirt"
> (->Price 45.99 21 "EURO"))
> (->Product "P-1231" "Table" "Coffee Table" (->Price 375 21
> "EURO"))
> (->Product "P-3451" "Chairs" "Set of Four(4) chairs"
> (->Price 200 21 "EURO"))
> (->Product "P-6781" "TableCloth" "Classic red and white
> checks 2m x 2m" (->Price 17.99 21 "EURO"))
> ])
>
> My requirement is to combine data from the two collections such that I can
> show the detailed product information for any item, for example:
>
> (->Item 3 "Shirt" "Slim Fit White Vest Shirt" (->Price 45.99
> 21 "EURO") 1 true)
>
> When I tried to use merge-with union I had an error which surprised me
> since I thought records are also maps:
>
> user=> (merge-with union items products)
> ClassCastException user.Product cannot be cast to java.util.Map$Entry
> clojure.core/key (core.clj:1465)
>
> Although I will fight on, any tips from any of you that have done this
> before would be greatly helped.
>
> Thanks
>
> ray
>
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