this is interesting, and it amounts to that you built your own ORM on
top of SA's SQL construction language, with some help from the SQL
generated by Mappers.
while you have addressed the issue of aggregates, which is important
for large tables, i dont see that youve addressed the issue of
dependencies/cascading here. I.e. what if some other tables depended
on the User table, how will you handle those records before you
delete all IDs less than 47 ?
if i were to integrate this with SA as an extension, i'd want it to
be constructed first as a separate object that looks more like:
m = mapper(MyClass, mytable)
manager = SimplePersist(m)
manager.update(obj1, obj2, obj3...)
manager.insert(obj1, obj2, obj3...)
manger.delete(....)
since SA's basic design idea is based around decoupling classes from
the way they are persisted.
then to provide the interface you describe below, you could either
provide an enhanced version of "assign_mapper" to monkeypatch the
additional methods, and/or provide a MixIn class that provides the
methods using inheritance, insuring that it works nicely with the
ActiveMapper since this falls right in with that whole thing.
also note that objects currently allow access to the "columns" that
are mapped to them via the interface: User.c.user_id.
On Mar 15, 2006, at 9:56 AM, Aaron Bickell wrote:
I recently ported a pretty large project over sqlalchemy, and it
was pretty smooth, but I kept running into the same few minor
snags. Mainly, I found that I kept on wanting to use the lower
level table api within the same transaction as mapped objects that
I'm modifying. Because modifications to the objects aren't
persisted until objectstore.commit() is called, I had to do a lot
of juggling to make this work. What I came up with to solve this
was a very thin, simple object layer on top of the table api that
gives some nice object abstraction, but is able to act directly on
the database rather than defer all operations to the objectstore.
I whipped up a module that lets you do the following, using a
metaclass:
class User(SimpleObject):
class table:
_table = user_table # same old user table from all the examples
u = User()
u.user_name = 'jimbob'
u.password = 'biscuits'
u.insert()
print u.user_id # <- the insert() populated the id (good for logging)
users = User.select(User.user_name.like('jim%'))
# the User class has attributes are the columns from the table
print users # a list of user objects
u.user_name = 'steve-o'
u.update() # updates the object with the new values
u.delete() # delete the object i created
User.delete_where(User.user_id<47) # deletes a bunch of users,
works the same for update
u = User.get(109) # gets the user by the primary key
This approach cuts out the objectstore which takes away the ability
for sqlalchemy to manage relations for you, but because the objects
have update/delete methods on the objects, so the problem is still
manageable. The User object could pretty easily have a method that
fetches the objects related to this object (preferences, addresses,
etc). This approach was particularly useful for my application
because I was modifying/deleting a lot of data in any given
transaction, and it filled the gap between mapped objects and
tables very nicely for me. Would others find this a useful
abstraction of the table api? Is there already a better way of
doing this that I missed? I'd gladly provide the code if anyone
was interested (after i clean it up). SQLAlchemy has been great to
use, and solves a lot of the problems I had continually fought for
a while.
Aaron Bickell
Research & Development
Optio Software, Inc
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