Hi Pete. Thank you for your reply. I have been interested in a similar integration of SQLAlchemy with Zope as SQLObject and it was evident other folks are already using it in Z3. I was curious how people have been dealing with transactions with some hope that something could be formalized with SQLAlchemy in a package. I am happy Jurgen is setting up something in SVN. SQLAlchemy is a very solid ORM and provides some excellent functionality.

Regards,
David



Pete Taylor wrote:
Hi David,
Currently, i'm not doing anything too terribly complicated with
sqlalchemy.  the real app i'm working on is doing something slightly
more complicated, but as an example...

<code>
from sqlalchemy import Table, Integer, String, Column, Boolean
from petetest.rdb import engine
#engine is just a mysql pool defined elsewhere

users = Table('users', engine,
        Column('user_id', Integer, primary_key=True),
        Column('active', Boolean),
        Column('full_name', String),
        Column('email', String),
    )

from zope.interface import implements
from sqlalchemy import mapper
from zope.app.folder import Folder
from interfaces import IUser

class User(Folder):
    """simple user class"""
    implements(IUser)
    active = True
    full_name = u''
    email = u''
User.mapper = mapper(User, users)
</code>

and User is now mapped to an rdb table named users.  any and all
manipulation on the object is followed by sqlalchemy.

the only significant issue i've run into so far, and it was a simple
enough fix, was that the zodb serializes the _sa_session_id attached
to the mapped object.  when you pull an old object back up to edit it
in whatever view you have associated, the zodb will deserialize a
no-longer-valid _sa_session_id.  what i ended up doing was creating a
session explicitly, using session.import_instance() on the current
context's object, importing it to a tmp object, and then swapping the
_sa_session_id.  i'm certain there are better ways to do it, but i'm a
bit of a sqlalchemy newbie.

really then, the update logic is pretty simple.  so long as you
super() your update first in the update from editview and use
session.commit() before the established session goes out of scope, it
should consistently update your object's mappings, both in the zodb
and in mysql.

the nice thing is, you can just as easily add attributes and such to
your class, have them contain things, etc...  the reason i didn't care
for sqlos or sqlobject is that when you create an object with those
ORM's, you derive from them.  i like being able to create my objects
as i see fit, making them the kind of content i want, and then just
mapping back what i need to make more conventionally (sql queryish)
available.

what i'm working on right now is determining where and how i need to
have sqlalchemy commit (either via session or objectstore directly)
when mapped objects are added programmatically, and not through a
specific edit view.  it's simple enough to know when to call commit
when there's an update action associated with it, but if objects are
updated and/or added via utility, i haven't yet figured out exactly
how/where to place my commits, but from what i've looked at, it
shouldn't be too difficult.

that may have been too long winded ;)  i hope it answered your
question some though.  if anyone else out there is using sqlalchemy
and zope3, i'd love to hear comments and suggestions.  I'm a neophyte
when it comes to integrating the two.  i'm sure there are better ways
than i'm currently going about it.

On 4/3/06, David Pratt <[EMAIL PROTECTED]> wrote:

Hi Pete. I have been looking at SQLAlchemy for Zope3. Can you advise how
 you are using this with zope's transactions. It seems that there are
some folks using SQLAlchemy with Zope3 for sure. I am hoping to see a
few things formalized somewhere or some work on assembling a small
package like SQLOS did for SQLObject. I think SQLAlchemy is a more
feature rich ORM and am simply looking for a way to use it in Zope3.

Regards,
David

Pete Taylor wrote:

I agree with Marco that the use case i can most readily imagine for
needing to tie zodb objects back to an rdb is to allow people to run
reports or get at historical data in more conventional ways...

I've had to make allowances for that in a number of projects i'm
currently working on for zope3...  this may not be immediately
helpful, but sqlalchemy (http://www.sqlalchemy.org) provides a really
nice way to simply write your classes as you would, tie the relevant
elements back to an rdb with a simple mapper on the class, without
restricting your class design too much.

as an example, i have a BTreeContainer derivative that maps a number
of it's Bool, TextLine, and Date attributes to a msyql database, while
letting other objects it contains be treated just like any other
BTreeContainer.  So long as you tie the sqlalchemy's sessions in
correction and commit when you know the zodb will be committing, it's
been pretty seamless so far, for my experience.

i admit, tables i'm using are not complex, nor are the objects that
are tied to them, so your mileage may vary...

On 4/3/06, Pete Taylor <[EMAIL PROTECTED]> wrote:


-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On
Behalf Of Marco Mariani
Sent: Monday, April 03, 2006 1:14 PM
To: Andreas Jung; [EMAIL PROTECTED]; zope3-users@zope.org
Subject: Re: [Zope3-Users] ZODB storage ways

Andreas Jung wrote:



I am searching for a way to change transparently the storage of ZODB

from file-base to a relational database. In general, Zope books

state, that this is possible.


one solution:

<http://hathawaymix.org/Software/PGStorage>

Unfortunately, pickles are not even remotely a SQL datatype... :)

I guess many people just want a SQL backend to allow queries from third
parties in the way they are used to.

If I do NOT want to be able to modify the data via SQL, and performance
is not a concern (not huge systems..), wouldn't it be better to "adapt"
:-) the data structure to a DBMS backend, with sane natural keys, but
without the hassle of advanced integrity constraints?

After all, as Joe Celko says, a table is not a (file|class) and a row is
not a (record|instance).. the structure we manipulate objects in ZODB is
not always the one we would like to use to perform SQL queries.

I mean, not dumping the whole ZODB on the DBMS, but run a few SQL
commands whenever an object "the clerks are interested into" changes its
state or data, gets deleted or whatever.

This, and adding a dump function to wipe out and recreate the SQL DB
should we have the need (structure changes, whatever).

I've yet to look at zope events, maybe it can be done without too much
effort?


_______________________________________________
Zope3-users mailing list
Zope3-users@zope.org
http://mail.zope.org/mailman/listinfo/zope3-users




--
"All guilt is relative, loyalty counts, and never let your conscience
be your guide."
 - Lucas Buck, American Gothic
_______________________________________________
Zope3-users mailing list
Zope3-users@zope.org
http://mail.zope.org/mailman/listinfo/zope3-users




--
"All guilt is relative, loyalty counts, and never let your conscience
be your guide."
  - Lucas Buck, American Gothic

_______________________________________________
Zope3-users mailing list
Zope3-users@zope.org
http://mail.zope.org/mailman/listinfo/zope3-users

Reply via email to