Il 05/08/11 20.33, Mark Erbaugh ha scritto:
On Aug 5, 2011, at 2:00 PM, Stefano Fontanelli wrote:
Il 05/08/11 19.29, Mark Erbaugh ha scritto:
In a declaratively created table, is there an automatic way to get a new
instance of the class object to be populated with values specified in a
'default' clause?
i.e.
class MyTable(Base):
__tablename__ = 'table'
name = Column(String, default='new name')
...
newRow = MyTable()
is there a way to have newRow.name automatically have the value 'new name'
before it is committed to the database? The best I've been able to come up
with so far is to use a 'CONSTANT' in the default clause and use that same
CONSTANT to initialize the field in the class' __init__, but this doesn't seem
very DRY.
Or, maybe is this the wrong question? Maybe I'm trying to do things the wrong
way. I'm trying to use mostly the same code add a new row or edit an existing
row. If the user is adding a record, I create a new instance of the class and
use the add/edit screen to edit the data. If the user is editing an existing
row, I retrieve the row, then use the add/edit screen with it.
Thanks,
Mark
Hi Mark,
to fill with defaults you can do:
newRow = MyTable()
session.add(newRow)
session.flush()
print newRow.name
'print newRow.name' will display 'new name'
To use the same code for create/update I suggest you to use session.merge:
http://www.sqlalchemy.org/docs/orm/session.html#merging
Stefano,
Thanks for the reply. The problem I see with this approach is that I think it
actually commits the new row to the database. In the app, it's possible that
the user could decide to cancel before inserting the new row. Of course, I
could back out the addition, but it seems like it would be better to not insert
in the first place.
I understand, but why can you not use session.rollback and session.commit?
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Ing. Stefano Fontanelli
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