On Sep 18, 2008, at 6:27 AM, GHZ wrote:
>
> Hi,
>
> I have a database table : 'Child' that contains the parent_id and
> grandparent_id. Foreign keys are present for both.
>
> I'm using declarative
>
> What is best practice to have the grandparent_id column set correctly
> when I insert?
>
> class GrandParent(Base):
> __tablename__ = 'grandparent'
> __table_args__ = {'autoload' : True, 'useexisting' : True}
> children = relation('Parent', backref=backref('parents')
>
> class Parent(Base):
> __tablename__ = 'parent'
> __table_args__ = {'autoload' : True, 'useexisting' : True}
> children = relation('Child', backref=backref('parents')
>
> class Child(Base):
> # Table has parent_id and grandparent_id columns
> __tablename__ = 'child'
> __table_args__ = {'autoload' : True, 'useexisting' : True}
>
>
> grandparent = GrandParent()
> parent = Parent()
> child = Child()
>
> grandparent.children = [parent]
> parent.children = [child]
>
> When I flush, I want child.grandparent_id to be set to the newly
> created grandparent.
theres two general ways:
1. quick and dirty: use a before_insert()/before_update()
MapperExtension which sets the "grandparent_id" column on Child. If
Child also had a relation() to GrandParent, you'd want to expire() it
too.
2. more involved: catch change events and populate a Child.grandparent
relation(). 0.5 has made the AttributeExtension API public which
would be a good place to catch this event. The advantage to this is
that your Child has a "grandparent" already set before any SQL is
issued to the database.
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