Many-to-one relationship in SQLAlchemy
- by Arrieta
This is a beginner-level question.
I have a catalog of mtypes:
mtype_id name
1 'mtype1'
2 'mtype2'
[etc]
and a catalog of Objects, which must have an associated mtype:
obj_id mtype_id name
1 1 'obj1'
2 1 'obj2'
3 2 'obj3'
[etc]
I am trying to do this in SQLAlchemy by creating the following schemas:
mtypes_table = Table('mtypes', metadata,
Column('mtype_id', Integer, primary_key=True),
Column('name', String(50), nullable=False, unique=True),
)
objs_table = Table('objects', metadata,
Column('obj_id', Integer, primary_key=True),
Column('mtype_id', None, ForeignKey('mtypes.mtype_id')),
Column('name', String(50), nullable=False, unique=True),
)
mapper(MType, mtypes_table)
mapper(MyObject, objs_table,
properties={'mtype':Relationship(MType, backref='objs', cascade="all, delete-orphan")}
)
When I try to add a simple element like:
mtype1 = MType('mtype1')
obj1 = MyObject('obj1')
obj1.mtype=mtype1
session.add(obj1)
I get the error:
AttributeError: 'NoneType' object has no attribute 'cascade_iterator'
Any ideas?
