On Dec 2, 2010, at 6:48 AM, neurino wrote:
> Let's say I have acquisitions at regular intervals and each
> acquisition I get different measures.
>
> Each meausre has a value and a numeric type id (1 = temperature, 2 =
> humidity ecc...)
>
> I want user to insert text description for type id he knows, if he
> wants.
>
> I end up having this 3 tables:
>
> measures = Table('measure', metadata,
>Column('id', Integer, primary_key=True),
>Column('acq_id', Integer, ForeignKey('acquisitions.id'),
>nullable=False)
>Column('type_id', Integer, ForeignKey('types.id'),
>nullable=False),
>Column('value', Float, nullable=False),
>)
>
> acquisitions = Table('acquisitions', metadata,
>Column('id', Integer, primary_key=True),
>Column('datetime', DateTime, nullable=False),
>)
>
> types = Table('types', metadata,
>Column('id', Integer, primary_key=True, autoincrement=False),
>Column('desc', String, nullable=False),
>)
>
> [class definitions...]
>
> orm.mapper(Acquisition, acquisitions)
> orm.mapper(Type, types)
> orm.mapper(Measures, measure, properties={
>'type': orm.relationship(Type, backref='measures'),
>'acquisition': orm.relationship(Acquisition, backref='measures'),
>})
>
> Now, while I want, deleting an acquisition, all child measures are
> deleted too,
>
> I DON'T want any modification in data if the user edit types, for
> example:
>
> - deletes a type (related measures are not deleted and their type_id
> is not changed in null value)
>
> - edits the type.id (precedent associated measures are not updated to
> new type_id but mantain the old one).
>
> How can I achieve this?
> I guess I should use cascade in relationship but can't figure how
>
> Thanks for your support!
the cascade to delete child items when parent is deleted here would be:
'acquisition': orm.relationship(Acquisition, backref=backref('measures',
cascade='all, delete-orphan'))
>
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