[postmodern-devel] Submarine announcement

[Ryszard Szopa]

On 9/1/07, Marijn Haverbeke <marijnh at gmail.com> wrote:
> Here is one way in which you could approach it: On the Lisp side, you
> can just let people define tables in any order, since non-existant
> foreign targets aren't a problem there. When creating a whole
> 'database schema' at once in the database, just create the tables
> first, and then the keys, and let any errors generated by non-existant
> tables go through. When creating or resetting a single table, if it
> has any foreign keys into tables that do not exist, check whether such
> a table is defined on the Lisp side -- if it is, raise an exception
> with a 'create this table' restart, otherwise, raise an unrecoverable
> exception.
>
> (This might, of course, have some problems that I haven't thought of
> yet, but I think it would be workable.)

I was thinking about something similar, but I was afraid of one
situation. Imagine the user actually forgets to define a class he
references to. Swallowing all the db errors would mean that he has
something that seems to work, and only in some specific situations
will start behaving strangely. This may lead to errors very hard to
debug.

Also, the creation of an SQL table is a shared-initialize :after
method of db-class. This means that there's no need of an additional
command to creating a table or all the tables -- it's all done at
definition time. The drawback of this approach is that I cannot
compute the dependencies between tables and reorder them so that
Postgres is happy.

On Friday I've implemented nearly exactly what I have written in my
letter from Thursday (when there's a non-existing referenced table
problem, the constraint adding function is stored; after the
initialization of each new db-class, all delayed constraints are
tried). And, apparently, it seems to work. When the user tries to make
an instance of a class that has unresolved dependencies, submarine
raises an error.

> Will submarine also have possibilities to define sequences, stored
> procs, and views? It would be cool to have a single place to define
> whole db schemas in Lisp, and then have convenient ways to create them
> all at once in an actual database. -- And of course, the hypothetical
> 'automatically detect differences between the schema defined in Lisp
> and the one existing in the database and interactively update the
> database' functionality might also be something you can think about --
> if Jaap allows you to waste another two months on this, hah.

I think Jaap won't mind, as I am going back to Poland next Friday.
(Uh-oh... That also means he'll stop paying me... oh, rats... ;))

The "checking if the table in the database complies to the
specification of the db-class" of submarine is nearly finished
(checking constraints is the only thing left to be written).

As for my plans for the future: I will be thinking about inheritance
(fortunately Postgres supports multiple inheritance), schemata (I
think they should be somehow related CL packages, because they seem to
be doing a very similar job). As for stored procs: I am not really
sure what could I do with them (it's a pity Postgres doesn't support
writing procedures in CL, like it does for Scheme).

Also, I would find it very fortunate if S-SQL supported ALTER,
constraints and stuff like that (I am using just quick hacks to
generate the appropriate SQL code right now, and I can't say to be
very happy about it). As you are on vacation, it probably means I
should do it myself. :P

BTW: how did it take for you to get a project at c-l.net? Because I
sent them an e-mail as they wanted and I still haven't received any
answer.

Bests,
    -- Richard
-- 
http://szopa.tasak.gda.pl/