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/[email protected]/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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