le 27.06.2007 15:36 Michael Bayer a écrit:
> 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).
>
Thanks Mickael,
I first tried to add the backref on only one side but the relationship
was not bi-directional ; user.addresses.append(a) updated address.user
but not the other way, that's why I added it both sides.
Then, with backrefs defined on both "add_property", I had a look at the
structures created at the mapper level (properties, reverse_property,
...) and they seemed coherent but I was not sure it was enough.
The only difference I saw is that you could find the backref "field" in
the properties list of both sides but the PropertyLoader objects were
coherent (User.mapper.properties['addresses'].reverse_property ==
Address.mapper.properties['user'] and
Address.mapper.properties['user'].reverse_property ==
User.mapper.properties['addresses']) and is_backref was positionned on
one side and not the other as you say it is needed below...
> 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).
>
>
OK, I'll do it that way if it is the supported way. Thanks for the hint.
Does the "is_backref" needs to be on a specific side of the relation ??
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