Hi Luke,
Thanks!
Initially CQL0.1 was motivated by "everything in Clojure" which was
the driving design principle behind the first version of CQL. When
I scrapped that project (for reasons you can read on my blog) I
instead turned my attention towards Relational Algebra as this
gives you unique ways to compose and express your queries, in
my opinion far superior to the SQL language itself.
Example from our test suite: Lets say you want to define a table
which computes an aggregate on a column, ex counting pictures
by user id and then join those stats to your users table. In CQL
you will (hopefully) intuitively write:
(let [photo-counts (-> (table :photos)
(aggregate [[:count/* :as :cnt]]
[:id])))]
(-> (table :users)
(join photo-counts (= {:users.id :photos.id}))
I think thats really as simple as you can express that join operation.
However for the SQL to work/be efficient, you need to detect when
a join benefits from spawning subselects and ClojureQL handles this
for you completely transparently, so if you execute the above
statement
the following is actually generated and run:
"SELECT users.*,photos_aggregation.cnt FROM users
LEFT OUTER JOIN
(SELECT photos.user_id,count(photos.*) AS cnt FROM photos GROUP BY
user_id)
AS photos_aggregation ON (users.user_id = photos_aggregation.user_id)"
And notice how your reference to :id in photos is automatically
aliased
to photos_aggregation. There are SQL statements which are truely
complex
and it takes a long time to master SQL and get comfortable with such
queries.
It is my ambition that ClojureQL will take away that complexity while
still
generating the most efficient SQL statements possible. The
implications for
Q/A on your projects will be substantial I hope.
And even if I was only doing CRUD - I'd prefer to do it (and have my
developers do it)
in Clojure, which is guaranteed to compile to correct SQL.
Answers your question?
Lau
On Nov 24, 1:56 am, Luke VanderHart <luke.vanderh...@gmail.com> wrote:
> Lau,
>
> This is really impressive, and I can't wait to experiment with it.
>
> That said, I'm curious as to what good use cases for this would be,
> and what it's motivation is. SQL is already a highly specialized DSL
> for slinging around relational data that most developers are already
> pretty good with. I'm wondering how useful it is to have a separate
> relational DSL. Is this motivated by the same "everything in Clojure"
> philosophy (like Hiccup or Scriptjure)? Not that there's anything
> wrong with that... I'm just curious as to use cases.
>
> Or does it confer some other benefit over SQL besides being Clojure?
> The only thing I see is the ability to reuse and compose fragments of
> relational logic. Unarguably, that is very cool, but off the top of my
> head I can't think of any particular benefit it would give, at least
> in my apps. 99% of my database interaction is a fixed set of CRUD
> operations, which (unless I'm missing something) would be just as easy
> to write in SQL directly.
>
> Thanks,
> -Luke
>
> On Nov 18, 2:10 pm, LauJensen <lau.jen...@bestinclass.dk> wrote:
>
> > Hi gents,
>
> > For those of you who have followed the development
> > of ClojureQL over the past 2.5 years you'll be excited
> > to know that ClojureQL is as of today being released
> > as 1.0.0 beta1.
>
> > That means that the significant primitives from Relational
> > Algebra are all in place and functional. The documentation
> > is there and I've even made a screencast in order to get
> > you guys started.
>
> > Personally Im excited about this version because it really
> > does change the way you work with a database. Queries
> > are incredibly composable!
>
> > For more information, please checkout this blogpost +
> > screencast:http://bestinclass.dk/index.clj/2010/11/clojureql--1.0.0-now-in-beta....
>
> > Best regards,
> > Lau
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