1. check on the isolation level you're using, and as a guarantee that
you read new rows, make sure the second "reader" session is beginning
its transaction *after* the first transaction is completed.
2. if the second session wishes to re-read the rows within its own
transaction, and you are using a lower isolation level like
read-committed, you can first call session.expire_all(), or the
populate_existing() method on the Query which will force a refresh of
objects as rows are read.
https://en.wikipedia.org/wiki/Isolation_%28database_systems%29
http://docs.sqlalchemy.org/en/rel_1_0/orm/session_transaction.html?highlight=isolation#setting-transaction-isolation-levels
http://docs.sqlalchemy.org/en/rel_1_0/orm/session_transaction.html#managing-transactions
http://docs.sqlalchemy.org/en/rel_1_0/orm/session_state_management.html#session-expire
http://docs.sqlalchemy.org/en/rel_1_0/orm/session_api.html?highlight=expire_all#sqlalchemy.orm.session.Session.expire_all
http://docs.sqlalchemy.org/en/rel_1_0/orm/query.html?highlight=populate_existing#sqlalchemy.orm.query.Query.populate_existing
On 6/22/15 8:38 PM, Balaji Pattewar wrote:
Hi all,
I am using simple SQLALCHEMY implementation.
I have two classes Svc, Mani
class Svc(Base):
''' class to map 'service' table in database
'''
__tablename__ = 'svc'
__table_args__ = {'autoload': True}
manis = relationship('Mani')
What I found that upon issuing session.query(Svc).all()
only refreshes Svc (svctable) entries from the database, but the manis
collection
is queried only once (on first query ) and it is not refreshed every time
session.query(Svc)
is issued.
What should I set so that manis collection should issue query and refresh and
sync itself with database everytime it is accessed or atleast everytime
session.query(Svc).all is issued.
You can see in detail steps for the issue.
I have two different session connected to the database using two different
terminals.
-------------------------------
In terminal I
svcs = session.query(Svc).all()
svc1 = svcs[0]
(halt)
------------------------------
In terminal II
svcs = session.query(Svc).all()
svc1 = svcs[0]
for mani in svc1.manis:
printmani.name <http://mani.name>
(halt)
----------------------------------
In terminal I
(continue from previous state)
test_mani = Mani()
svc1.manis.append(test_mani)
session.commit()
# New test_mani is commited to DB
# Do the query
svcs = session.query(Svc).all()
svc1 = svcs[0]
for mani in svc1.manis:
printmani.name <http://mani.name>
# The new mani is printed
(halt)
--------------------------------
In terminal II
(continue from previous state)
requery
svcs = session.query(Svc).all()
svc1 = svcs[0]
for mani in svc1.manis:
printmani.name <http://mani.name>
# The newly added test_mani is not part of
# svc1.mani even after Svc is requried.
Thanks in advance for your guidance.
regards
Balaji
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