Re: another n00b defrecord combination question
Great stuff Ben. Thanks.
ray
On Saturday, December 15, 2012 10:54:42 PM UTC+1, Benjamin R. Haskell wrote:
On Sat, 15 Dec 2012, mond wrote:
Thanks for picking up the cudgels Ben!
Ha. It's nice to have reached a point where I feel at-all confident
with any of this... happy to help.
To be honest I am struggling to repeat your advice in the REPL. In
any case, I decided to change the data structures in line with your
advice and put the IDs into maps rather than the records.
(defrecord Item [name product quantity purchased])
(defrecord Product [name description prices])
(defrecord Price [price tax currency])
(def items [ {:id 1 :item (-Item Brogues P-123 1 true)}
{:id 2 :item (-Item Underpants P-345 2 false)}
{:id 3 :item (-Item Shirt P-678 1 true)} ])
(def carts [ (-Cart Birthday (first items))
(-Cart Xmas (rest items)) ])
(def products [ {:id P-1231 :product (-Product Table Coffee Table
(-Price 375 21 EURO))}
{:id P-3451 :product (-Product Chairs Set of
Four(4) chairs (-Price 200 21 EURO))}
{:id P-123 :product (-Product Brogues Men's
Leather Slip on Brogues (-Price 93.00 21 EURO))}
{:id P-345 :product (-Product Underpants CK Y
Fronts (-Price 23.50 21 EURO))}
{:id P-678 :product (-Product Shirt Slim Fit White
Vest Shirt (-Price 45.99 21 EURO))}
{:id P-6781 :product (-Product TableCloth Classic
red and white checks 2m x 2m (-Price 17.99 21 EURO))} ])
Do you think the zipmap is still the way to go (to resolve the
'foreign key' or could there be an easier way? I guess the fact that
only items have to zipmapped is one advantage.
It seems like items and products should still have an :id property, so I
don't think you need to detach the ID from its entity. The zipmap'ed
version is useful as an index, not really as its own structure. So, it
ends up as just a single map (not an array of maps) with ID's as keys,
and the corresponding entity as the value:
(defrecord Item [id name product quantity purchased])
(defrecord Product [id name description prices])
(defrecord Price [price tax currency])
(def items [ (-Item 1 Brogues P-123 1 true)
(-Item 2 Underpants P-345 2 false)
(-Item 3 Shirt P-678 1 true) ])
(def products [ (-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-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-6781 TableCloth Classic red and white
checks 2m x 2m (-Price 17.99 21 EURO)) ])
; two useful indexes(/indices?):
(def prod-item
An index from Product ID to an Item
(zipmap (map :product items) items))
(def id-product
An index from Product ID to a Product
(zipmap (map :id products) products))
; Then you can use that to get the products joined with their items:
(defn product-with-item
Find the Item info and merge it into the product, without overwriting
:id
[product]
(merge-with (fn [a b] a) product (prod-item (:id product
; example usage:
(product-with-item (id-product P-345))
;= #user.Product{:id 2,
; :name Underpants,
; :description CK Y Fronts,
; :prices #user.Price{:price 23.5, :tax 21, :currency
EURO},
; :purchased false,
; :quantity 2,
; :product P-345}
(def joined-products (map product-with-item products))
;= A list of all the products joined with their items
--
Best,
Ben
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Re: another n00b defrecord combination question
One small thing Ben... when I try to use the final formulation I receive an
error:
(def joined-products (map product-with-item products))
user= (joined-products)
ClassCastException clojure.lang.LazySeq cannot be cast to clojure.lang.IFn
user/eval241 (NO_SOURCE_FILE:9)
Any ideas?
Thanks in advance
ray
On Saturday, December 15, 2012 10:54:42 PM UTC+1, Benjamin R. Haskell wrote:
On Sat, 15 Dec 2012, mond wrote:
Thanks for picking up the cudgels Ben!
Ha. It's nice to have reached a point where I feel at-all confident
with any of this... happy to help.
To be honest I am struggling to repeat your advice in the REPL. In
any case, I decided to change the data structures in line with your
advice and put the IDs into maps rather than the records.
(defrecord Item [name product quantity purchased])
(defrecord Product [name description prices])
(defrecord Price [price tax currency])
(def items [ {:id 1 :item (-Item Brogues P-123 1 true)}
{:id 2 :item (-Item Underpants P-345 2 false)}
{:id 3 :item (-Item Shirt P-678 1 true)} ])
(def carts [ (-Cart Birthday (first items))
(-Cart Xmas (rest items)) ])
(def products [ {:id P-1231 :product (-Product Table Coffee Table
(-Price 375 21 EURO))}
{:id P-3451 :product (-Product Chairs Set of
Four(4) chairs (-Price 200 21 EURO))}
{:id P-123 :product (-Product Brogues Men's
Leather Slip on Brogues (-Price 93.00 21 EURO))}
{:id P-345 :product (-Product Underpants CK Y
Fronts (-Price 23.50 21 EURO))}
{:id P-678 :product (-Product Shirt Slim Fit White
Vest Shirt (-Price 45.99 21 EURO))}
{:id P-6781 :product (-Product TableCloth Classic
red and white checks 2m x 2m (-Price 17.99 21 EURO))} ])
Do you think the zipmap is still the way to go (to resolve the
'foreign key' or could there be an easier way? I guess the fact that
only items have to zipmapped is one advantage.
It seems like items and products should still have an :id property, so I
don't think you need to detach the ID from its entity. The zipmap'ed
version is useful as an index, not really as its own structure. So, it
ends up as just a single map (not an array of maps) with ID's as keys,
and the corresponding entity as the value:
(defrecord Item [id name product quantity purchased])
(defrecord Product [id name description prices])
(defrecord Price [price tax currency])
(def items [ (-Item 1 Brogues P-123 1 true)
(-Item 2 Underpants P-345 2 false)
(-Item 3 Shirt P-678 1 true) ])
(def products [ (-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-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-6781 TableCloth Classic red and white
checks 2m x 2m (-Price 17.99 21 EURO)) ])
; two useful indexes(/indices?):
(def prod-item
An index from Product ID to an Item
(zipmap (map :product items) items))
(def id-product
An index from Product ID to a Product
(zipmap (map :id products) products))
; Then you can use that to get the products joined with their items:
(defn product-with-item
Find the Item info and merge it into the product, without overwriting
:id
[product]
(merge-with (fn [a b] a) product (prod-item (:id product
; example usage:
(product-with-item (id-product P-345))
;= #user.Product{:id 2,
; :name Underpants,
; :description CK Y Fronts,
; :prices #user.Price{:price 23.5, :tax 21, :currency
EURO},
; :purchased false,
; :quantity 2,
; :product P-345}
(def joined-products (map product-with-item products))
;= A list of all the products joined with their items
--
Best,
Ben
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Re: another n00b defrecord combination question
On Sun, 16 Dec 2012, mond wrote:
One small thing Ben... when I try to use the final formulation I receive an
error:
(def joined-products (map product-with-item products))
user= (joined-products)
ClassCastException clojure.lang.LazySeq cannot be cast to clojure.lang.IFn
user/eval241 (NO_SOURCE_FILE:9)
Any ideas?
To evaluate a list, Clojure tries to call the first element as a
function, with the remaining elements as its arguments. So, in this
case:
(joined-products)
Clojure tries to cast the first element of the list (joined-products) to
be used as a Clojure function (clojure.lang.IFn), but it's a lazy
sequence (clojure.lang.LazySeq).
You just don't need the list:
user= joined-products
(#user.Product{...} #user.Product{...} #user.Product{...} ...)
--
Best,
Ben
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Re: another n00b defrecord combination question
Hilarious - I am so conditioned already to have everything in a list :)
Thanks for your patient explanation. Merry xmas.
ray
Ray
On Sunday 16 December 2012 at 22:20, Benjamin R. Haskell wrote:
On Sun, 16 Dec 2012, mond wrote:
One small thing Ben... when I try to use the final formulation I receive an
error:
(def joined-products (map product-with-item products))
user= (joined-products)
ClassCastException clojure.lang.LazySeq cannot be cast to clojure.lang.IFn
user/eval241 (NO_SOURCE_FILE:9)
Any ideas?
To evaluate a list, Clojure tries to call the first element as a
function, with the remaining elements as its arguments. So, in this
case:
(joined-products)
Clojure tries to cast the first element of the list (joined-products) to
be used as a Clojure function (clojure.lang.IFn), but it's a lazy
sequence (clojure.lang.LazySeq).
You just don't need the list:
user= joined-products
(#user.Product{...} #user.Product{...} #user.Product{...} ...)
--
Best,
Ben
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Re: another n00b defrecord combination question
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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Re: another n00b defrecord combination question
I think I am close to answering this myself (which is always nice!) I have done the necessary joins with map and I can return a product description user= (map (fn [item product] (= (:product item (:id product))) (:description product)) items products) (Men's Leather Slip on Brogues CK Y Fronts Slim Fit White Vest Shirt) Or a purchased status for the matching item user= (map (fn [item product] (= (:product item (:id product))) (:purchased item)) items products) (true false true) But I have my knickers in a twist when I want to get more than one value out or a combination of values. user= (map (fn [item product] (= (:product item (:id product))) (:id item :description product)) items products) (user= IllegalArgumentException Wrong number of args passed to keyword: :id clojure.lang.Keyword.throwArity (Keyword.java:85) So does anyone have the last bit of syntax to help me take back a list of values from the inputs? Thanks ray On Saturday, December 15, 2012 5:25:59 PM UTC+1, 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 -- You received this message because you are subscribed to the Google Groups Clojure group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
Re: another n00b defrecord combination question
OK - I have it now: (map (fn [item product] (= (:product item (:id product))) [(:id item) (:description product)]) items products) This feels OK to me but if anyone has a nicer / more idiomatic solution, I will be happy to take feedback. ray On Saturday, December 15, 2012 7:08:21 PM UTC+1, mond wrote: I think I am close to answering this myself (which is always nice!) I have done the necessary joins with map and I can return a product description user= (map (fn [item product] (= (:product item (:id product))) (:description product)) items products) (Men's Leather Slip on Brogues CK Y Fronts Slim Fit White Vest Shirt) Or a purchased status for the matching item user= (map (fn [item product] (= (:product item (:id product))) (:purchased item)) items products) (true false true) But I have my knickers in a twist when I want to get more than one value out or a combination of values. user= (map (fn [item product] (= (:product item (:id product))) (:id item :description product)) items products) (user= IllegalArgumentException Wrong number of args passed to keyword: :id clojure.lang.Keyword.throwArity (Keyword.java:85) So does anyone have the last bit of syntax to help me take back a list of values from the inputs? Thanks ray On Saturday, December 15, 2012 5:25:59 PM UTC+1, 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$Entry clojure.core/key (core.clj:1465) Although I will fight on, any tips from any of you that have done this before would be greatly helped. Thanks ray -- You received this message because you are subscribed to the Google Groups Clojure group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
Re: another n00b defrecord combination question
(responses inline)
On Sat, 15 Dec 2012, mond wrote:
I have defined these types of records for modelling a simple shopping cart:
; An item in the cart
(defrecord Item [id name product quantity purchased])
; The product that relates to the item in the cart
(defrecord Product [id name description prices])
; A price definition
(defrecord Price [price tax-rate currency])
; Sample items
(def items [
(-Item 1 Brogues P-123 1 true)
(-Item 2 Underpants P-345 1 false)
(-Item 3 Shirt P-678 1 true)
])
; Sample products
(def products [
(-Product P-123 Brogues Men's Leather Slip on
Brogues (-Price 93.00 21 EURO))
(-Product P-345 Underpants CK Y Fronts (-Price
23.50 21 EURO))
(-Product P-678 Shirt Slim Fit White Vest Shirt
(-Price 45.99 21 EURO))
(-Product P-1231 Table Coffee Table (-Price 375 21
EURO))
(-Product P-3451 Chairs Set of Four(4) chairs
(-Price 200 21 EURO))
(-Product P-6781 TableCloth Classic red and white
checks 2m x 2m (-Price 17.99 21 EURO))
])
My requirement is to combine data from the two collections such that I can
show the detailed product information for any item, for example:
(-Item 3 Shirt Slim Fit White Vest Shirt (-Price 45.99 21
EURO) 1 true)
When I tried to use merge-with union I had an error which surprised me
since I thought records are also maps:
user= (merge-with union items products)
ClassCastException user.Product cannot be cast to java.util.Map$Entry
clojure.core/key (core.clj:1465)
It looks like your second response worked around it, but for anyone
following along: merge-with takes two or more maps, and uses the
function you pass to merge the values of common keys. So, the error is
caused because merge-with expects items and products to be maps (not
vectors of map-like things).
On Sat, 15 Dec 2012, mond wrote:
I think I am close to answering this myself (which is always nice!)
I have done the necessary joins with map and I can return a product
description
user= (map (fn [item product] (= (:product item (:id product)))
(:description product)) items products)
(Men's Leather Slip on Brogues CK Y Fronts Slim Fit White Vest Shirt)
The (= (:product item (:id product))) here is being ignored.
It works because your example arrays happen to have the items and
products lined up properly (first three products match the items
in order):
(map (fn [item product]
(= (:product item (:id product))) ; the result of this comparison is
thrown away
(:description product) ; this is the value that is returned
) items products)
If you want to match things up, you might be better off creating maps
for each category of thing:
; (with items and products as you'd defined them before)
(def product-item (zipmap (map :product items) items))
;= {P-123 #user.Item{...}, P-345 #user.Item{...}, ...}
(def id-product (zipmap (map :id products) products))
;= {P-123 #user.Product{...}, P-345 #user.Product{...}, ...}
(def combined (merge-with union product-item id-product))
;= {P-123 #user.Product{... with :quantity and :purchased },
;P-1231 #user.Product{... with no Item keys ...}, ...etc.
Or a purchased status for the matching item
user= (map (fn [item product] (= (:product item (:id product)))
(:purchased item)) items products)
(true false true)
But I have my knickers in a twist when I want to get more than one
value out or a combination of values.
user= (map (fn [item product] (= (:product item (:id product))) (:id item
:description product)) items products)
(user= IllegalArgumentException Wrong number of args passed to keyword:
:id clojure.lang.Keyword.throwArity (Keyword.java:85)
So does anyone have the last bit of syntax to help me take back a list
of values from the inputs?
Other than the matching issue (the = form isn't being used -- see
above), the problem with what you've written is that you want a map,
rather than a list:
(map (fn [item product] {:id item :description product}) items products)
Or if you really want a list, you need to quote it:
(map (fn [item product] '(:id item :description product)) items products)
--
Best,
Ben
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Re: another n00b defrecord combination question
On Sat, 15 Dec 2012, Benjamin R. Haskell wrote: Or if you really want a list, you need to quote it: (map (fn [item product] '(:id item :description product)) items products) Oops, wrong. Rather, you would want clojure.core/list: (map (fn [item product] (list :id item :description product)) items products) -- Best, Ben -- You received this message because you are subscribed to the Google Groups Clojure group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
Re: another n00b defrecord combination question
Thanks for picking up the cudgels Ben!
To be honest I am struggling to repeat your advice in the REPL. In any
case, I decided to change the data structures in line with your advice and
put the IDs into maps rather than the records.
(defrecord Item [name product quantity purchased])
(defrecord Product [name description prices])
(defrecord Price [price tax currency])
(def items [ {:id 1 :item (-Item Brogues P-123 1 true)}
{:id 2 :item (-Item Underpants P-345 2 false)}
{:id 3 :item (-Item Shirt P-678 1 true)} ])
(def carts [ (-Cart Birthday (first items))
(-Cart Xmas (rest items)) ])
(def products [ {:id P-1231 :product (-Product Table Coffee Table
(-Price 375 21 EURO))}
{:id P-3451 :product (-Product Chairs Set of Four(4)
chairs (-Price 200 21 EURO))}
{:id P-123 :product (-Product Brogues Men's Leather
Slip on Brogues (-Price 93.00 21 EURO))}
{:id P-345 :product (-Product Underpants CK Y Fronts
(-Price 23.50 21 EURO))}
{:id P-678 :product (-Product Shirt Slim Fit White
Vest Shirt (-Price 45.99 21 EURO))}
{:id P-6781 :product (-Product TableCloth Classic red
and white checks 2m x 2m (-Price 17.99 21 EURO))} ])
Do you think the zipmap is still the way to go (to resolve the 'foreign
key' or could there be an easier way? I guess the fact that only items have
to zipmapped is one advantage.
Thanks for your support
ray
On Saturday, December 15, 2012 7:53:32 PM UTC+1, Benjamin R. Haskell wrote:
On Sat, 15 Dec 2012, Benjamin R. Haskell wrote:
Or if you really want a list, you need to quote it:
(map (fn [item product] '(:id item :description product)) items
products)
Oops, wrong. Rather, you would want clojure.core/list:
(map (fn [item product] (list :id item :description product)) items
products)
--
Best,
Ben
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Re: another n00b defrecord combination question
On Sat, 15 Dec 2012, mond wrote:
Thanks for picking up the cudgels Ben!
Ha. It's nice to have reached a point where I feel at-all confident
with any of this... happy to help.
To be honest I am struggling to repeat your advice in the REPL. In
any case, I decided to change the data structures in line with your
advice and put the IDs into maps rather than the records.
(defrecord Item [name product quantity purchased])
(defrecord Product [name description prices])
(defrecord Price [price tax currency])
(def items [ {:id 1 :item (-Item Brogues P-123 1 true)}
{:id 2 :item (-Item Underpants P-345 2 false)}
{:id 3 :item (-Item Shirt P-678 1 true)} ])
(def carts [ (-Cart Birthday (first items))
(-Cart Xmas (rest items)) ])
(def products [ {:id P-1231 :product (-Product Table Coffee Table (-Price 375 21
EURO))}
{:id P-3451 :product (-Product Chairs Set of Four(4) chairs
(-Price 200 21 EURO))}
{:id P-123 :product (-Product Brogues Men's Leather Slip on Brogues
(-Price 93.00 21 EURO))}
{:id P-345 :product (-Product Underpants CK Y Fronts (-Price
23.50 21 EURO))}
{:id P-678 :product (-Product Shirt Slim Fit White Vest Shirt
(-Price 45.99 21 EURO))}
{:id P-6781 :product (-Product TableCloth Classic red and white checks 2m x
2m (-Price 17.99 21 EURO))} ])
Do you think the zipmap is still the way to go (to resolve the
'foreign key' or could there be an easier way? I guess the fact that
only items have to zipmapped is one advantage.
It seems like items and products should still have an :id property, so I
don't think you need to detach the ID from its entity. The zipmap'ed
version is useful as an index, not really as its own structure. So, it
ends up as just a single map (not an array of maps) with ID's as keys,
and the corresponding entity as the value:
(defrecord Item [id name product quantity purchased])
(defrecord Product [id name description prices])
(defrecord Price [price tax currency])
(def items [ (-Item 1 Brogues P-123 1 true)
(-Item 2 Underpants P-345 2 false)
(-Item 3 Shirt P-678 1 true) ])
(def products [ (-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-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-6781 TableCloth Classic red and white checks 2m x 2m
(-Price 17.99 21 EURO)) ])
; two useful indexes(/indices?):
(def prod-item
An index from Product ID to an Item
(zipmap (map :product items) items))
(def id-product
An index from Product ID to a Product
(zipmap (map :id products) products))
; Then you can use that to get the products joined with their items:
(defn product-with-item
Find the Item info and merge it into the product, without overwriting :id
[product]
(merge-with (fn [a b] a) product (prod-item (:id product
; example usage:
(product-with-item (id-product P-345))
;= #user.Product{:id 2,
; :name Underpants,
; :description CK Y Fronts,
; :prices #user.Price{:price 23.5, :tax 21, :currency EURO},
; :purchased false,
; :quantity 2,
; :product P-345}
(def joined-products (map product-with-item products))
;= A list of all the products joined with their items
--
Best,
Ben
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