Re: OO Patch - Mailing list pgsql-hackers

> CREATE TABLE SHAPE( ..);
> CREATE TABLE SQUARE(x1, y1, x2, y2) INHERITS(shape);
> CREATE TABLE CIRCLE(x, y, radius) INHERITS(shape);
> 
> I can't just go SELECT * FROM SHAPE and call some C++ method to display
> the shape on the screen. If I maintain an attribute in SHAPE called
> "classname" manually, then I can SELECT * FROM SHAPE, and then do a
> separate query on the subclass when I know the type - very inefficient.
> Or I can do 3 separate queries. But then I'm hosed when I add a TRIANGLE
> type.
> 
> What I really want is..
> 
> Result r = Query<Shape>.select("SELECT ** FROM SHAPE");
> foreach(r, item) {
>     item->display();
> }
> 
> Which still will work when I add a triangle. I.e. typical polymorphism
> code maintenance advantage.
> 
> Which is what object databases do or an object relational mapper like
> Persistance do. Without that ability I would argue there's very limited
> point in having inheritance at all.
> 
I can agree with that. As I wrote a relational mapper for Smalltalk/X
based on the libpq API I noticed the same problems, when doing mapping on 
tables.
But some questions/comments about that:
a) How are the indices handled ? If I define an index on an attribute   defined in TABLE SHAPE all subclasses are also
handledby this index   or do we have an index for the base table and each sub table on    this attribute ?
 
b) Please do not make the libpq API too compilcated ! It's a charm how   small the API is and how easy the initial
connectionto a psqgl   database is -- compare it against the ODBC API ....
 
b.1)   Despite the ODBC API I rather would like to see to enhance the idea    of result   sets supported by the
libpq-API.I do not need to query each tuple   what it delivers to me. I would like to open the result, query   the
structureand then handle the data. If the database returns   multiple different sets (results from different tables):
ok:do it the    same way for each result set.
 
b.2)   There were some postings about other delivering methods to retrieve   the information from each tuple. Today we
getan ASCII-representation   of the result tuple and the client has to convert it.
 
   Some were not very happy about it, but I like it. Some were concerned   about the fact, that they have to copy the
resultto the information   structure within their software. When you use software systems, which    are based on
garbagecollection systems, then one ALMOST EVER has   to do it.
 
c)   I would like to see more ideas about the extension of pgsql to become   an active database. The notification
systenis not enough, because   it does not return the most interesting informations.
 
   I myself would like to see something like the VERSANT event system.
d)    Please only add basic, language independent, support for    inheritance - special features can very often better
simulatedby   software on the client side. The best example is the introduction   of sequences.
 


Marten