Hi,
The following script is then followed by its output, and finally by the
table output.
I don't get what is going on here. Yes, I should commit the session, and
the table is empty as expected, but why does the id keep incrementing on
successive runs, and where is this table living, if not in the db? I'd
expect to see the id stay at 1. Also, I'd expect to see something in
session.dirty. Deleting the table resets the counter back to 1, so it
looks like it is using the table in some way, but as already stated, the
table shows as empty via a select * command.
If anyone can clarify what is going on here and satisfy my curiosity, I'd
appreciate it. Please CC me on any reply. Thanks.
Regards, Faheem.
***************************************************************
oddity.py
***************************************************************
from sqlalchemy import *
from sqlalchemy.orm import mapper, relation, sessionmaker
def add_obj(session, obj):
""" Check if object primary key exists in db. If so,exit, else
add.
"""
from sqlalchemy import and_
from sqlalchemy.orm import object_mapper
mapper = object_mapper(obj)
pid = mapper.primary_key_from_instance(obj)
criterion = and_(*(col == val for col, val in zip(mapper.primary_key,
mapper.primary_key_from_instance(obj))))
if session.query(obj.__class__).filter(criterion).count() > 0:
print "%s object with id %s is already in
db."%(type(obj).__name__, pid)
exit
else:
session.add(obj)
metadata = MetaData()
mytest_table = Table(
'mytest', metadata,
Column('id', Integer, primary_key=True),
)
class MyTest(object):
def __init__(self):
pass
mapper(MyTest, mytest_table)
dbstring = "postgres://username:pas...@localhost:5432/oddity"
db = create_engine(dbstring)
metadata.bind = db
metadata.create_all()
conn = db.connect()
Session = sessionmaker()
session = Session()
t1 = MyTest()
add_obj(session, t1)
print session.query(MyTest).count()
stmt = mytest_table.select()
for row in stmt.execute():
print row
stmt = select([mytest_table.c.id])
print "anno statement is %s\n"%stmt
for row in stmt.execute():
print row
print "session.dirty is %s"%session.dirty
#session.commit()
#session.flush()
#conn.close()
*************************************
script output
*************************************
$ python oddity.py
1
(1,)
anno statement is SELECT mytest.id
FROM mytest
(1,)
session.dirty is IdentitySet([])
$ python oddity.py
1
(2,)
anno statement is SELECT mytest.id
FROM mytest
(2,)
session.dirty is IdentitySet([])
************************************
table output
************************************
oddity=# select * from mytest;
id
----
(0 rows)
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