On Aug 23, 2010, at 5:37 AM, Freewind wrote:
> I'm new to python(sqlalchemy), and I'm learning to build web site with
> pylons and sqlalchemy.
>
> I have a problem when I declare the relationship between models. I've
> tried it several hours, but failed. But I think it should be a basic
> question.
>
> I have two classes: User and Article, user can create articles, and
> modified the other people's article(like wiki).
> So a user has created-articles and edited-articles.
>
>
> class Article(Base):
> __tablename__ = 'articles'
>
> id = Column(Integer, primary_key=True)
> title = ...
>
> user_id = Column(Integer, ForeignKey('users.id'))
> editor_id = Column(Integer, ForeignKey('users.id'))
>
> # relations
> user = relationship('User', backref='articles') # -> has error
>
>
> class User(Base):
> pass
>
>
> But there is an error displayed:
> InvalidRequestError: One or more mappers failed to compile. Exception
> was probably suppressed within a hasattr() call. Message was: Could
> not determine join condition between parent/child tables on
> relationship Article.user. Specify a 'primaryjoin' expression. If this
> is a many-to-many relationship, 'secondaryjoin' is needed as well.
>
> I tried to add `primaryjoin` to the line('has error'), but don't know
> what it should be. I tried some codes, but none works.
you want to say this:
class Article(Base):
__tablename__ = 'articles'
id = Column(Integer, primary_key=True)
user_id = Column(Integer, ForeignKey('users.id'))
editor_id = Column(Integer, ForeignKey('users.id'))
user = relationship('User', backref='articles',
primaryjoin="Article.user_id==User.id")
class User(Base):
__tablename__ = 'users'
id = Column(Integer, primary_key=True)
this to resolve the ambiguity of how Article would join to User, given that
there are two different foreign keys that reference the 'users' table.
Background documentation is at:
http://www.sqlalchemy.org/docs/mappers.html?highlight=primaryjoin#specifying-alternate-join-conditions-to-relationship
the quoting is specific to declarative:
http://www.sqlalchemy.org/docs/reference/ext/declarative.html?highlight=primaryjoin#configuring-relationships
>
> Thank you in advance!
>
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