On Feb 8, 2012, at 9:39 AM, cropr wrote:
> I aam having an issue defining a 2nd foreign key constraint on 2
> derived classes of a base class that uses a self referential join.
>
> Base class:ContentBase
>
> class ContentBase(Base):
> __tablename__ = 'content'
> __mapper_args__ = {'polymorphic_on': ctype,
> 'polymorphic_identity':'contentbase'}
> id = Column(types.Integer, primary_key=True, autoincrement=True)
> children = relationship("ContentBase", backref=backref('parent',
> remote_side=id))
> ....
>
> Derived class CdRoot
>
> class CdRoot(ContentBase):
> __tablename__ = 'cdroot'
> __mapper_args__ = {'polymorphic_identity' : 'cdroot'}
> contentType = 'CdRoot'
> id = Column(types.Integer, ForeignKey(ContentBase.id),
> primary_key=True)
> clubs = relationship('CdClub', primaryjoin="cdroot.id ==
> cdclub.cdroot_id")
> ...
>
> Derived class CdClub
>
> class CdClub(ContentBase):
> __tablename__ = 'cdclub'
> __mapper_args__ = {'polymorphic_identity' : 'cdclub'}
> id = Column(types.Integer, ForeignKey(ContentBase.id),
> primary_key=True)
> cdroot_id = Column(types.Integer, ForeignKey(CdRoot.id))
> ...
>
> The 2nd join between CdRoot and CdClub fails with the message : Can't
> determine join between content and
> cdclub, tables have more than one FK constraint.
>
> Apparently the primaryjoin condition is not sufficient to get rid of
> the error. Any clue how to solve this
Assuming this is paraphrasing since "cdroot.id==cdclub.cdroot_id" doesn't have
the correct casing, also there's a relationship on ContentBase that doesn't
appear to refer to any column but I assume that's under your "...".
Filling in the blanks with reasonable guesses it works fine:
from sqlalchemy import *
from sqlalchemy.orm import *
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.ext.associationproxy import association_proxy
Base= declarative_base()
class ContentBase(Base):
__tablename__ = 'content'
id = Column(Integer, primary_key=True, autoincrement=True)
ctype = Column(String)
parent_id = Column(Integer, ForeignKey('content.id'))
children = relationship("ContentBase",
backref=backref('parent',remote_side=id))
__mapper_args__ = {'polymorphic_on':
ctype,'polymorphic_identity':'contentbase'}
class CdRoot(ContentBase):
__tablename__ = 'cdroot'
__mapper_args__ = {'polymorphic_identity' : 'cdroot'}
contentType = 'CdRoot'
id = Column(Integer, ForeignKey(ContentBase.id),primary_key=True)
clubs = relationship('CdClub', primaryjoin="CdRoot.id ==CdClub.cdroot_id")
class CdClub(ContentBase):
__tablename__ = 'cdclub'
__mapper_args__ = {'polymorphic_identity' : 'cdclub'}
id = Column(Integer, ForeignKey(ContentBase.id),primary_key=True)
cdroot_id = Column(Integer, ForeignKey(CdRoot.id))
configure_mappers()
if you still have problems, please provide a fully working example, thanks !
>
> Ruben
>
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