Michael Bayer wrote:
for thing in session.query(MyThing).all():
... print x.id, x.name, x.value, x.valid_from, x.valid_to
1, 'foo', 100, 2010-06-29 09:00, 2010-06-29 09:05
2, 'foo', 200, 2010-06-29 09:05, None
`x` used to correspond to the row with id of 1, but now corresponds to the row
with the id of 2. That's the effect I'm looking to achieve.
I've added that recipe here
http://www.sqlalchemy.org/trac/wiki/UsageRecipes/VersionedRows
Sweet. A few questions:
- why do we need to refresh self.id in case it has expired? Doesn't the
very next line(s) get rid of self.id?
- if the implementation of new_version was generic, I'm guessing we
could live without the mixin?
- I take it there are no problems with specifying multiple extensions to
sessionmaker? (we need zope.sqlalchemy's extension too) What effect does
order of extensions have?
- why do we ignore instance states without an identity in before_flush?
- only primary objects in one table
that's not what your example above illustrates....
Well, I guess I meant there's only one table for each mapped class and
there's only one active row per instance in the table at any one time.
(I'd like to validate the latter, since users will be able to optionally
set valid_from and valid_to; is before_flush the right place? Is
session.query legit to use there? What exceptions are legit to raise
from within before_flush to indicate validation failure?)
- the valid_from and valid_to form a linked list of version validity
using the recipe I linked, you'd establish that linkage in the new_version()
method
Okay, and I guess I can use
attributes.get_history(instance,'valid_from') and
attributes.get_history(instance,'valid_to') to see if these attributes
have been explicitly set?
Where is the History record returned by get_history documented?
- only certain column changes cause a new version to be created (eg: if the
'notes' column changes, we don't want to create a new version; would
session.is_modified() still help with that?)
using the recipe I linked, you'd add some logic into before_flush() that does
attributes.get_history(x, 'foo') for each attribute that you care about,
instead of using session.is_modified() which is across the board
Cool.
cheers,
Chris
--
Simplistix - Content Management, Batch Processing & Python Consulting
- http://www.simplistix.co.uk
--
You received this message because you are subscribed to the Google Groups
"sqlalchemy" group.
To post to this group, send email to sqlalch...@googlegroups.com.
To unsubscribe from this group, send email to
sqlalchemy+unsubscr...@googlegroups.com.
For more options, visit this group at
http://groups.google.com/group/sqlalchemy?hl=en.
