That was indeed my problem, thank you very much! But I still cannot
wrap my brain around cascading, if anyone has a link to a good writeup
I'd be glad.
--tom
On Jul 13, 12:51 am, Conor <conor.edward.da...@gmail.com> wrote:
> On 07/12/2010 02:38 PM, tom wrote:
>
>
>
>
>
> > Hi,
>
> > I have a problem with cascading a delete. I have two tables, and they
> > are mapped many-to-many:
>
> > class File(object): pass
> > file_table = Table('file', metadata,
> > Column('id', Integer, primary_key=True, autoincrement=True),
> > Column('filename', String(255)),
> > }
>
> > class FileHost(object): pass
> > file_host = Table('host', metadata,
> > Column('id', Integer, primary_key=True, autoincrement=True ),
> > Column('name', String(255)),
> > )
>
> > file_hosted = Table('file_hosted', metadata,
> > Column('id_host', Integer, ForeignKey('host.id')),
> > Column('id_file', Integer, ForeignKey('file.id'))
> > )
>
> > session.mapper(File, file_table, properties={
> > 'host': relation(FileHost, secondary=file_hosted, backref='files',
> > cascade='all,delete-orphan', single_parent=True)
> > })
> > session.mapper(FileHost, file_host)
>
> > This is the error I get:
> > sqlalchemy.exc.IntegrityError: (IntegrityError) update or delete on
> > table "file" violates foreign key constraint
> > "file_hosted_id_file_fkey" on table "file_hosted"
> > DETAIL: Key (id)=(50905) is still referenced from table
> > "file_hosted".
>
> > Can somebody please tell me what I'm doing wrong because I tried to
> > find an answer and couldn't. This was the only somewhat related thing
> > I
> > found:http://www.mail-archive.com/sqlalchemy@googlegroups.com/msg13198.html
>
> You are telling SQLAlchemy to cascade File deletes to FileHost, but you
> want it the other way around. You can fix this by moving the
> cascade='all,delete-orphan' and single_parent=True clauses into the
> backref. You also probably want use_list=False.
>
> session.mapper(File, file_table, properties={
> 'host': relation(FileHost,
> backref=backref('files',
> cascade='all,delete-orphan',
> single_parent=True),
> secondary=file_hosted,
> use_list=False)
>
> })
>
> -Conor
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