On Jul 23, 2006, at 4:12 AM, Darryl Cousins wrote:

Gary Poster wrote:
If the relationship is intrinsic to one object's data model but not
to the other's, then it makes sense to have a Python pointer on the
first object.

Hi Gary,

Am I right that 'a Python pointer on the first object' is defined by
simply defining the schema field, eg::

        mypointer = Object(
                        title="Pointer to object",

Then everything else will fall into place. I could even use formlib to
edit the object being pointed to from within a form editing the 'first

The second object would not even know it is pointed to. For it to know I
would need to use a relationship as you go on to discuss.

Have a correctly understood?

Yes, precisely; and for what it is worth, the Object schema value lets formlib work, and specifies part of your software's "contract", but is not necessary for the most basic story. The simplest clear case (Where `app` represents some ZODB folder, like the application root):

class DemoSubject(persistent.Persistent):

class DemoObject(persistent.Persistent):

app['demo'] = DemoSubject()
app['demo'].mypointer = DemoObject()

By the way, a small but possibly important subtlety about the object widgets that are associated with the schema object fields is that (unless you manage your form pretty carefully) they change value by creating new instances of the sub-object and replacing it on the main object, not by modifying an old sub-object instance, IIRC.

Sometimes Choice fields with a custom vocabulary or source are what you want, if you want to make a pointer to an object that already exists somewhere in the database.

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