I just started playing with sqlalchemy. At the moment I am working
with one database, but properly I need to work with severall database
at the same time, but I want to work in such a way, that I do not need
to know in which database a certain table resides.
Is this possible?
For example it looks like it is possible for the session object.
I use in a model file (through an import):
#####
import sqlalchemy as sa
import sqlalchemy.orm as sa_orm
metadata = sa.MetaData('sqlite:////home/cecil/databases/metingen.db')
engine = metadata.bind
Session = sa_orm.sessionmaker()
session = Session()
gewichtTable = sa.Table(
'gewicht', metadata,
sa.Column('id', sa.Integer, primary_key = True),
sa.Column('datum', sa.Date, nullable = False, unique = True),
sa.Column('gewicht', sa.Float, nullable = False),
sa.Column('vet', sa.Float, nullable = False),
sa.Column('water', sa.Float, nullable = False),
sa.Column('spieren', sa.Float, nullable = False),
)
class Gewicht(object):
def __repr__(self):
return '<Gewicht: %10.10s, %5.1f, %5.1f, %5.1f, %5.1f>' %
(self.datum, self.gewicht, self.vet, self.water, self.spieren)
sa_orm.mapper(Gewicht, gewichtTable)
#####
In the main program I have:
#####
import sqlalchemy as sa
import sqlalchemy.orm as sa_orm
Session = sa_orm.sessionmaker()
session = Session()
from metingen_model import Gewicht, gewichtTable
#####
And later on I do:
#####
for row in session.query(Gewicht).all():
#####
And this does what it should do. So I expect that the engine is
fetched out of Gewicht.
First I had:
for row in engine.execute('SELECT MIN(gewicht) AS gewicht '
', MIN(vet) AS vet '
', MAX(water) AS water '
', MAX(spieren) AS spieren '
'FROM gewicht '):
but because I want it to have the code engine independend I changed that to:
for row in sa.select([sa.func.min(Gewicht.gewicht)
, sa.func.min(Gewicht.vet)
, sa.func.max(Gewicht.water)
, sa.func.max(Gewicht.spieren)]).execute():
The problem with this is that I now need to use row[0] instead of
row.gewicht. Is there a way to use row.gewicht also in the case
sa.select?
Is this a good way of doing things, or should I work with severall engines?
Also sqlalchemy and sqlalchemy.orm are now imported in the main
program and in metingen_model. And later on they will become imported
in even more modules. Is this a problem? I was told that Python was
intelligent enough to see that sqlalchemy and sqlalchemy.orm are
allready imported and that importing again should not have
-significant- consequences. Is that true?
--
Cecil Westerhof
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