On Jul 25, 2011, at 9:47 AM, Aviv Giladi wrote:
> I can't seem to make cascade deletes work in sqlalchemy.
>
> I have a parent class (called Rating), a sub class (Subrating) and a
> third class called SubRatingProperty.
>
> There is a one-to-one relationship between Rating and SubRating - each
> Rating can only have one specific SubRating object. Next, the
> SubRatingProperty refers to a row in a table with fixed values. There
> are 3 SubRatingProperty entries - property1, property2 and property3.
> The SubRating class can have one or more of either property1,
> property2 and property3, therefore the relationship is many-to-many (a
> SubRatingProperty can have more than one properties, and for example
> property1 can be assigned to more than one SubRatingProperty's).
>
> Here is the code that defines all of this:
>
> subrating_subratingproperty_association =
> Table('subrating_subratingproperty_association', Base.metadata,
> Column('subrating_id', Integer,
> ForeignKey('subratings.id')),
> Column('subrating_property_id',
> Integer, ForeignKey('subrating_properties.id')))
>
> class SubRatingProperty(Base):
> __tablename__ = 'subrating_properties'
> id = Column(Integer, primary_key=True)
> name = Column(Unicode(32), unique=True)
> subratings = relationship("SubRating",
>
> secondary=subrating_subratingproperty_association,
> backref="subrating_properties")
>
> class SubRating(Base):
> __tablename__ = 'subratings'
> id = Column(Integer, primary_key=True)
> name = Column(Unicode(32), unique=True)
>
> class Rating(Base):
> __tablename__ = 'ratings'
> id = Column(Integer, primary_key=True)
> name = Column(Unicode(32), unique=True)
> subrating_id = Column(Integer, ForeignKey('subratings.id'))
> subrating = relationship("SubRating", backref=backref("rating",
> uselist=False))
> Everything works fine, but I can't figure out how to do cascade
> deletes. I am deleting Rating objects, and when I do, I would like the
> according SubRating object to be deleted, as well as all the entries
> in the association table. So deleting Rating1 would delete its
> SubRating, as well as all the connection between the SubRating and
> SubRatingProperty's.
>
> I have tried adding cascade="all" to the relationship call,
you have two relationships() here to build the full chain so you'd need
"cascade='all, delete-orphan'" on both Rating.subrating as well as
SubRating.subrating_properties (use the backref() function instead of a string
to establish the cascade rule on that end.
> and I also
> tried adding ondelete="cascade") to the ForeignKey call.
if all the involved FOREIGN KEYs are generated with ON DELETE CASCADE as this
would accomplish, as long as you are not on SQLIte or MySQL MyISAM the deletes
will be unconditional.
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