Re: [Sqlalchemy-users] Socal Python group: SA Presentation

Tue, 12 Sep 2006 08:45:29 -0700

if theyre the types that dont like ORMs, you might also want to stress that SA can be used to construct straight SQL in a database-neutral fashion, and the orm package need not be used (functions like mapper(), relation() etc. all come from sqlalchemy.orm).   ive seen a lot of projects that prefer to use it in this manner, where the ultimate result is that the project implements its own "mini-ORM" using SA just as an abstraction from the database (and particularly in the way databases differ in primary key generation).

if you want to really impress them show them this trick, which illustrates just how abstracted it is (illustrates LEFT OUTER JOIN using Postgres and oracle 8 which doesnt support 'LEFT OUTER JOIN'):

from sqlalchemy import *

import sqlalchemy.databases.postgres as postgres
import sqlalchemy.databases.oracle as oracle

pg_dialect = postgres.dialect()
oracle8_dialect = oracle.dialect(use_ansi=False)

meta = MetaData()
t1 = Table('tablea', meta,
        Column('id', Integer, primary_key=True),
        Column('value', String(30))
    )
t2 = Table('tableb', meta,
    Column('id', Integer, primary_key=True),
    Column('t1_id', Integer, ForeignKey('tablea.id')))
   
query = t1.outerjoin(t2).select()

print "Postgres version:", query.compile(dialect=pg_dialect)
print
print "Oracle 8 version:", query.compile(dialect=oracle8_dialect)


output:

Postgres version: SELECT tablea.id, tablea.value, tableb.id, tableb.t1_id
FROM tablea LEFT OUTER JOIN tableb ON tablea.id = tableb.t1_id

Oracle 8 version: SELECT tablea.id, tablea.value, tableb.id, tableb.t1_id
FROM tablea, tableb
WHERE tablea.id = tableb.t1_id(+)



On Sep 12, 2006, at 2:32 AM, Michael Carter wrote:

Hey everyone,

Tomorrow I'm presenting an introduction to SQLALchemy for the Socal Piggies (http://agile.unisonis.com/socalpiggies) meeting at Caltech. My first thought was to jump right in to the tutorial. I think though, that most people are still wondering about using an ORM at all. Either that, or they are coming strictly from the programming side and are interested in finding a way to persist their data. So I am going to begin with an introduction to Object-relational mapping and where SA fits into that picture before actually introducing any code. I figure I will spend a couple minutes on the differences between an ORM and an object database.

Let me know what you think about this approach. Has anyone else done an Introductory presentation on SA before?

Thanks,

Michael Carter
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