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ANN: Criteria 1.0

Ryan Pavlik

9/8/2003 7:29:00 AM

Criteria 1.0
============

Criteria is a module for abstracting queries to various data sets.
For instance, you might have a flat text file, or an array of Ruby
objects, or a SQL database, and wish to perform the same query on
any given source, without different versions of code for each.

This module was inspired by the work of flgr (on #ruby-talk) on
Junction, and the ENV.var work by h9k (also on #ruby-talk).

Here are some examples:

idx1 = SQLTable.new("orders")
q1 = (idx1.price > idx1.paid) & (idx1.duedate < Time.now.to_i)

q1.limit = 5
q1.order = :ASC
q1.order_by = idx1.name, idx1.age

puts q1.select

# => SELECT * FROM orders WHERE ((orders.price > orders.paid) AND
# (orders.duedate < 1062616643)) LIMIT 5 ORDER BY orders.name,
# orders.age ASC


The generic Table superclass with the same query:

idx2 = Table.new
q2 = (idx2.price > idx2.paid) & (idx2.duedate < Time.now.to_i)

puts q2.inspect
puts q1.inspect

# => (& (> :price :paid) (< :duedate 1062616719))
# => (& (> :price :paid) (< :duedate 1062616719))

The very simple 'mysql' table included works like SQLTable, except
it actually returns a MysqlRes for immediate use. There are other
included table types as well.

You can find Criteria at the following location:

http://mephle.org...

--
Ryan Pavlik <rpav@mephle.com>
2 Answers

Tim Bates

9/11/2003 12:15:00 AM

0

On Mon, Sep 08, 2003 at 04:28:53PM +0900, Ryan Pavlik wrote:
> Criteria 1.0
> ============
>
> Criteria is a module for abstracting queries to various data sets.
> For instance, you might have a flat text file, or an array of Ruby
> objects, or a SQL database, and wish to perform the same query on
> any given source, without different versions of code for each.
<snip>
> You can find Criteria at the following location:
>
> http://mephle.org...

From the above address:
Basics
------

To use the Critera module, it''s helpful to understand how it works.
The Table superclass is a class with most of the default instance
methods removed. Instead, when given a method (including any
operator methods), it generates a Criterion object in
#method_missing.

A Criterion is similar to a Table---it''s another nearly-blank class,
except it tracks the method call given to Table. It also chains to
another Criterion. When evaluated recursively along this chain, the
syntax of the statement can be restored.


When I first saw the previous email, I thought - how on earth can he do
that? It''s a way to abstract queries to any sort of interface -
something I''ve been trying to do for ages - and from the output it looks
like it''s somehow capturing the Ruby code and parsing it, but no; it''s
so much simpler than that. And done in only 65 lines of Ruby code. That
is some seriously, seriously funky magic. Ryan, I''m extremely impressed.
Once more the power of Ruby astounds me. The ability to translate the
same abstract Ruby query into SQL code or an array lookup is just
fantastic. Good work.

One of these days I''m going to have to take a look at Mephle. If it''s
anything like as good as this, I''m in!

Tim Bates
--
tim@bates.id.au

Ryan Pavlik

9/11/2003 12:33:00 AM

0

On Thu, 11 Sep 2003 09:15:29 +0900
Tim Bates <tim@bates.id.au> wrote:

<snip>
> [Criteria] is some seriously, seriously funky magic. Ryan, I''m
> extremely impressed. Once more the power of Ruby astounds me. The
> ability to translate the same abstract Ruby query into SQL code or
> an array lookup is just fantastic. Good work.

Well, it was highly inspired by flgr''s Junction code; that''s where
the basic magic came from. Glad you like it though. =)

> One of these days I''m going to have to take a look at Mephle. If it''s
> anything like as good as this, I''m in!

Mephle is less funky magic and more just doing mundane things for you.
If you do web stuff at all, you''ll probably find it takes a lot of
work out of the process; by 1.0 I hope to be able to say the same
about arbitrary GUI apps.

Thanks,

--
Ryan Pavlik <rpav@mephle.com>

"I sure as hell didn''t learn anything, if thats what you mean." - 8BT