Say you have a simple rule that if people pay within a timeframe they get a
X% discount
select ..... price*(1-X/100) from .... where ... paydate between
startdiscount and enddiscount
It is likely that there will be multiple SQL statements that will contain
some form of this rule. A good approach is to find a way to compose
multiple rules into a single query. There are many alternatives, views,
database functions, manipulating/aggregating clojure structures that
represent SQL queries.
To make matters worse, this simple rule will also have a counterpart in the
UI and possibly in other non SQL code. That is why a production system is
appealing to me. You could just write a rule like this.
(defrule timed-discount
( ....(between paydate startdiscount enddiscount) ... )
( ... (:price (* :price (- 1 (/ X 100) ) ) ) ....)
)
And it won't just create the SQL, but also be available for execution in
the JVM or in say clojure script. All because the rule is declarative by
nature. I think the shortcoming of ORM tools is that they bring a higher
level technology like SQL and lower it down to the low level of imperative
languages. A rule based system would not suffer from that problem.
On Wednesday, October 30, 2013 8:50:48 AM UTC-5, Ray Miller wrote:
>
> On 30 October 2013 11:47, Kris Jenkins <[email protected]
> <javascript:>>wrote:
>
>> FWIW, I too am interested in a better SQL tool for Clojure, but my take
>> on it is that we don't need a new language on top of SQL, but a better way
>> to use SQL directly.
>>
>> My thinking, plus an *alpha-grade* library, can be found here:
>> https://github.com/krisajenkins/yesql#rationale
>>
>
> Something similar I'm using in production on a couple of sites:
>
> https://github.com/ray1729/sql-phrasebook
>
> Ray.
>
>
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