Carl carld

Models, Roles, Decorators, and Interactions

A modest alternative to DCI that might be worth further thought

One of the problems with advancing the discussion on DCI is that we lack a comparable alternative pattern that has the same goals, but favors a low ceremony approach. The closest thing we have to that is Rails concerns, but they are more like distant relatives of the DCI concepts rather than first cousins, and that makes comparisions between the two approaches not especially fruitful.

I am considering the idea of experimenting with my own paradigm that captures the intent and purity of DCI, but with the convenience of concerns. Please note that this is just the starting point of a conversation, it is NOT a promise of comercially available cold fusion or a cure for cancer. It's just a gist with an idea on it I'd like to hear your thoughts on.

What if we had a top-level topology that was split into Models, **Rol

	# 1st way - do it automatically
	# AR decides if it's better to use JOIN or separate query
	User.includes(:profile)
	# -> join or separate query

	# 2nd way - always use JOIN
	User.eager_load(:profile)
	# -> SELECT `users`.`id` AS t0_r0, ..., `profiles`.`user_id` AS t1_r1, ... FROM `users` LEFT OUTER JOIN `profiles` ON `profiles`.`user_id` = `users`.`id`

	# 3rd way - always do separate query

	-- http://stackoverflow.com/questions/1124603/grouped-limit-in-postgresql-show-the-first-n-rows-for-each-group
	-- http://www.postgresql.jp/document/9.2/html/tutorial-window.html

	CREATE TABLE empsalary (
	depname varchar(10) not null
	, empno integer not null
	, salary integer not null
	);

	INSERT INTO empsalary (depname, empno, salary) VALUES ('develop', 11, 5200);

	// Try parser combinators in C
	#include <stdio.h>
	#include <stdlib.h>

	struct token
	{
	const char *text;
	};

	struct token_list

	;run in chez scheme 8.4
	;http://programmingpraxis.com/2013/01/15/translate-csv-to-html/
	;TODO: read csv file
	; parse csv file to a list
	(define (string-split sep str)
	(define (f cs xs) (cons (list->string (reverse cs)) xs))
	(let loop ((ss (string->list str)) (cs '()) (xs '()))
	(cond ((null? ss) (reverse (if (null? cs) xs (f cs xs))))
	((char=? (car ss) sep) (loop (cdr ss) '() (f cs xs)))
	(else (loop (cdr ss) (cons (car ss) cs) xs)))))

	;;By Jhen Kung, [email protected]
	;;app.rkt

	#lang racket(require web-server/servlet
	web-server/servlet-env
	"router.rkt")

	(serve/servlet mordor
	#:port 8080
	#:servlet-path "/"

	# Speed things up by not loading Rails env
	config.assets.initialize_on_precompile = false

	;; same as the merge function in MergeSort.scm
	(define (insert L M)
	(if (null? L) M
	(if (null? M) L
	(if (< (car L) (car M))
	(cons (car L) (insert (cdr L) M))
	(cons (car M) (insert (cdr M) L))))))

	;; another insert function
	;; need to modify the first para in insertionsort function to (car L)

	# Transforming the vanilla recursive fib into the iterative DP version
	# through a series of mechanical steps.
	#
	# For more on converting recursive algorithms into iterative ones, see:
	# http://blog.moertel.com/posts/2013-05-11-recursive-to-iterative.html


	# original function

	def fib(n):