On Aug 19, 2010, at 10:22 AM, sandro dentella wrote:
> Hi,
>
> Let's start with the simple example based on movie/director example
>
> class Director(Base):
> __tablename__ = 'director'
> id = Column(Integer, primary_key=True)
> last_name = Column(String(60), nullable=False)
> movies = relation('Movie', backref='director',
> cascade='all, delete-orphan',)
>
> class Movie(Base):
> __tablename__ = 'movie'
> id = Column(Integer, primary_key=True)
> title = Column(String(60), nullable=False)
> director_id = Column(Integer, ForeignKey('director.id'),
> nullable=False)
>
> Due to delete-orphan cascading rule when creating a movie object I
> need to
> attach a director object. In a table editor when setting a foreign key
> I
> parse all the properties to see if someone requires such 'director'
> obj so
> that I can easily fetch it and attach. The working code in 0.5 is as
> follows:
>
> def get_props_for_delete_orphan(mapper, field_name):
> """
> discover if field_name setting needs to set an object to
> fullfill the request
> for a delete_orphan cascading on a possible relation
> returns the generator for the properties or ()
> """
> prop = mapper.get_property(field_name)
> assert isinstance(prop, properties.ColumnProperty)
> assert len(prop.columns) == 1 # I don't handle mapper with two
> columns in a property
> column = prop.columns[0]
>
> props = []
> for pr in mapper.iterate_properties:
> if isinstance(pr, properties.RelationProperty):
> if pr.direction.name in ('MANYTOONE',):
> for col in pr.local_remote_pairs[0]:
> # I can't use col in p.local_remote_pairs
> # as it uses 'col == p.local_remote_pairs' that evaluates
> # to a BinaryExpression
> if column is col:
> try:
> if pr.backref.prop.cascade.delete_orphan:
> props += [pr]
> except AttributeError, e:
> pass
> return tuple(props)
>
> This fails in sqla 0.6 as pr.backref is empty. Which is the correct
> way to
> get the properties that have a backref that have cascade with
> delete_orphan?
why not put some "info" on the director_id column (i.e. Column(....,
info={'foo':'bar'}) ) that gives your application the information what you need
in a succinct and direct way. There's no public API that links relationships
to backrefs and the poking through lists of columns is hacky too. I could
tell you where they're linked but it can change at any time.
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