Thanks Michael,
and what about `type` relationship?
Or would it be much simpler have no relation at all, since there must
be no actions on children on parent update / delete?
If I had to do this with plain SQL I'd simply make a
`measures LEFT JOIN types ON measures.type_id = types.id`
to get type description, if any, so I realize probably the
relationship is not really needed...
Any advice welcome anyway...
Thank you
On Dec 2, 3:55 pm, Michael Bayer <mike...@zzzcomputing.com> wrote:
> 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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