On 08/26/2016 05:55 PM, Simon King wrote:
On 26 Aug 2016, at 21:42, adaptable (Metaframework) <rognoni....@gmail.com>
wrote:
Hi all,
this comment on Github is well formatted:
https://github.com/zzzeek/sqlalchemy/pull/295#issuecomment-242834334
I see the wrong todo.id after the commit (a log string instead 1)
[...]
2016-08-26 21:36:56,071 INFO sqlalchemy.engine.base.Engine COMMIT
######### before commit - id: None
2016-08-26 21:36:56,073 INFO sqlalchemy.engine.base.Engine BEGIN (implicit)
2016-08-26 21:36:56,073 INFO sqlalchemy.engine.base.Engine INSERT INTO todo
(description, done, user_id) VALUES (?, ?, ?)
2016-08-26 21:36:56,073 INFO sqlalchemy.engine.base.Engine ('TODO test', None,
None)
2016-08-26 21:36:56,074 INFO sqlalchemy.engine.base.Engine COMMIT
######### after commit - id: 2016-08-26 21:36:56,075 INFO
sqlalchemy.engine.base.Engine BEGIN (implicit)
2016-08-26 21:36:56,076 INFO sqlalchemy.engine.base.Engine SELECT todo.id AS
todo_id, todo.description AS todo_description, todo.done AS todo_done,
todo.user_id AS todo_user_id
FROM todo
WHERE todo.id = ?
2016-08-26 21:36:56,076 INFO sqlalchemy.engine.base.Engine (1,)
1
2016-08-26 21:36:56,077 INFO sqlalchemy.engine.base.Engine SELECT todo.id AS
todo_id, todo.description AS todo_description, todo.done AS todo_done,
todo.user_id AS todo_user_id
FROM todo
2016-08-26 21:36:56,077 INFO sqlalchemy.engine.base.Engine ()
1 TODO test
running this code on MAC (Python 2.7.10) with SQLAlchemy version 1.0.14
https://github.com/rognoni/adaptable/blob/master/Backend/Python-Flask/storage/sqlalchemy_sqlite.py
[...]
### test
session = db_schemas.examples.session()
todo = db_schemas.examples.classes.todo(description="TODO test")
session.add(todo)
print "######### before commit - id: ", todo.id
session.commit()
print "######### after commit - id: ", todo.id
for instance in session.query(db_schemas.examples.classes.todo):
print instance.id, instance.description
Using the query the instance.id is correct: 1
I think you are misunderstanding the output. The statement you are executing is:
yes! I just saw that too. OK :) thanks for jumping on this.
print "######### after commit - id: ", todo.id
Python is printing out the first part before it even tries to evaluate
“todo.id”. Then, when it goes to evaluate it, a database query is triggered
(because all the attributes of todo were expired after the commit). The query
output is logged to stdout. Then finally the print statement prints the value
of todo.id, which is the “1” on its own 6 lines further down.
Here’s a non-SQLAlchemy example demonstrating the same thing:
class A(object):
... @property
... def attribute(self):
... print 'some log output'
... return 'actual value'
...
a = A()
print 'the value is:', a.attribute
the value is: some log output
actual value
print 'using interpolation, the value is %s' % a.attribute
some log output
using interpolation, the value is actual value
When you use string interpolation, “a.attribute” has to be evaluated and
substituted into the string before the print statement can run.
If you use the print *function* rather than the print *statement*, all the
arguments will be evaluated before anything is displayed, so this also wouldn’t
happen.
Hope that helps,
Simon
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