Re: [SQLObject] One-to-one relationships

[Sam N. <sa...@se...>]

Gonzalo Sainz-Tr=E1paga wrote:
> Hi again,
> I've got a new problem with my model definitions.
> I have a "User" class and a "Person" class. I want to keep them
> separated because not all of the site's users are really Persons from
> the organization point of view - other people who have users are not
> registered as Persons (the root user, or maintenance users for employee=
s
> that need to upload stuff to my site).
>=20
> The "Person" is then the entity that is related to the rest of the data=
,
> and the "User" is mostly the login-and-id related data.
> I want to be able to link a "Person" object to a "User" one directly. A=
s
> i said, not all Users are a Person, so I want to have the ability to
> leave User.Person null.
>=20
> From rom what i've read this is what you call "inheritance", but the FA=
Q is
> not very clear on the subject and the solution proposed seems to fulfil=
l
> particular needs that i don't have.
>=20
> I can always have a unique table with user-data and person-data on it,
> just leaving the Person-type data blank when the user is not a Person,
> but i would like to avoid this.
>=20
> Any suggestions?

If you don't need the inheritance functionality, then no need to use it.=20
For my stuff (so far at least), I haven't felt the need for inheritance,=20
so I haven't checked it out, and I can't say how it works. Assuming that=20
you don't need inheritance, try this:

class Person(SQLObject):
	myVar1 =3D StringCol()
	myVar2 =3D StringCOl()
	...
	user =3D ForeignKey('User', default=3DNone)

class User(SQLObject):
	myVar1 =3D StringCol()
	myVar2 =3D StringCOl()
	...
	person =3D ForeignKey('Person', default=3DNone)

This way, a user doesn't have to have (be) a person, and a person=20
doesn't have to have (be) a user, but they can! There is one extra step=20
with this method. You have to set the foreign key in both objects, not=20
just one, like this:

user.person =3D myPerson # now we have proper mapping from user to person
person.user =3D user # now we have reverse mapping from person to user

You could also do this with MultipleJoins or RelatedJoins, but since you=20
  have a 1:1 mapping, you don't need to.

I recommend hanging out on the sqlobject documentation web page, reading=20
and rereading it. This is all covered (more or less), it just takes time=20
to sink in. Also, lurn on SQL logging and read the sql output that is=20
produced when you get/create/modify/delete/search sqlobject objects. At=20
least, that is what has helped me ;-).

Peace
- Sam