On Jun 27, 2007, at 6:00 AM, remi jolin wrote:
>
> Hello,
>
> Suppose we have the Address and User mappers as they are defined in
> SA's
> documentation
>
> I was wondering if the 2 syntax bellow were equivalent :
>
> 1/
> User.mapper.add_property('addresses', relation(Address,
> backref=BackRef('user', **user_args)), **addresses_args)
>
> 2/
> Address.mapper.add_property('user', backref='addresses', **user_args)
> User.mapper.add_property('addresses', backref='user',
> **addresses_args)
>
no, they are not. the example in 2. is incorrect. you only need one
property with a backref to set up the bi-directional relationship.
setting both properties in both directions will have the effect of
only some of the properties taking effect..and in an undefined way
(i.e. it might break).
the two equivalent conditions you have in mind are:
User.mapper.add_property('addresses',
relation(Address, backref=backref('user', **user_args)),
**addresses_args)
and
Address.mapper.add_property('user',
attributeext=attributes.GenericBackrefExtension('addresses'),
is_backref=True, **user_args)
User.mapper.add_property('addresses',
attributeext=attributes.GenericBackrefExtension('user'),
**addresses_args)
where GenericBackrefExtension handles bi-directional attribute
population, i.e. someaddress.user = User() firing off
someaddress.user.addresses.append(someaddress), and the "is_backref"
flag is needed to be on one side of the bi-directional relationship
in some cases during a flush() (currently, only in post_update
relations).
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