On Nov 10, 2003, at 11:43 AM, Mark A. Schwenk wrote:
>
> Although I may be using OODB's soon as the main persistence mechanism
> for some of my projects, I need connectivity and interoperability into
> the relational database world. But I'd like something very minimal and
> comprehensible. Something lighter weight than the Generic Light-Weight
> Object-Relational Persistence (GLORP) framework.
>
> I'd be interested in any info, code, and suggested directions for
> extending Roe.

You can go to http://beta4.com/mc/db , which contains the most recent 
Roe snapshots.

Very briefly:

Roe is "Relational Object Expressions" - it models the relational 
algebra as Smalltalk collection objects.  So, you have a Relation 
object for each table in your database that looks like a collection of 
tuples.  These can be combined with the standard relational operators - 
join, select, etc - which will produce new relation objects.  All of 
these are lazy - it is only when you try to access the contents of the 
collection (eg, through #do:) that a query corresponding to the 
relation is generated and sent out to the DB.

The main advantage from a mapping point of view is that once you've 
built a complex query in this way, you can introspect on it to figure 
out exactly what the resulting tuples will be - which columns of which 
tables they came from.  This means you can take the results of an 
arbitrary query and correctly map its rows into objects, something that 
wouldn't be possible with a query represented as a string of SQL.

Of course, it's also nice to have queries as first class objects that 
can be passed around and composed easily.

Roe supports multiple backends - it comes with one for PostgreSQL and 
one that doesn't use SQL at all, but performs all the operations very 
inefficiently in memory, which is useful for testing.

The SQL generation requires subqueries (unless you want to write some 
funky clause-reduction logic of some kind), so early versions of MySQL 
would be hard to support.

I'll try to put together some more detailed info (like where mapping 
would hook in) when I have time.  Meanwhile, browse the unit tests...

Avi