Re: [Modeling-users] EditingContext and Zope Sessions

[Sebastien B. <sbi...@us...>]

        Hi,

frobni barka <fro...@ya...> wrote:
> I have another question concerning the sample code at
> the main page.
>=20
> john.addToAddresses(a_john); a_john.setPerson(john)
>=20
> Wouldn't it be enough to just use one of the above
> statements, because they do the same thing?


No, it would not be enough, let's see why.

  As a general rule, the graph of objects hold by an EditingContext
  should be kept consistent. As the association is bi-directional in the
  PyModel exposed on the first page, both objects should be modified
  with the relevant informations.

This has nothing to do with RDBMS: imagine you just write:

>>> address_john.setPerson(john)

  This does not update 'john' itself, and its list of addresses will not
  contain the new addresses, that's why you also need to update the
  other side. They do not really /do/ the same thing, but they both
  participate in updating the association. In fact, that has little to
  do with the framework, except that the framework expects the graph of
  objects to be consistent --or it could make wrong decisions, in this
  case, it might incorrectly analyse the changes that have been made and
  as a consequence, not save the modifications as expected.

Now, every object in the framework inherits from CustomObject which has
a mix-in named 'RelationshipManipulation' that can ease the way you
update the relationships. It uses the model to determine what should be
done when you modify a relationship; for example,

>>> john.addObjectToBothSidesOfRelationshipWithKey(a_john, 'addresses')

  will update john and a_john in the same time. Moreover, imagine a_john
  was previously bound to john2, it will also remove a_john from john2's
  list of address. This is a convenient method, I think, that can be of
  some help. For further details about this, please see section 8.1 in
  the User's Guide:
http://modeling.sf.net/UserGuide/customobject-relationshipmanipulation.html


        Regards,

-- S=E9bastien.