After some discussion on #sqlalchemy, I solved this problem by moving
the declaration of the relationship outside of the class declaration
(see below).
Is this a good / common way of defining relationships?
class UIMetadata(db.Model):
""" Class to allow UI metadata to be associated with almost any
other class"""
__tablename__ = 'ui_metadata'
id = db.Column(db.Integer, primary_key=True)
class_type = db.Column(db.String)
class_id = db.Column(db.Integer)
label = db.Column(db.String)
def __init__(self, class_type, class_id, label):
self.class_type = class_type
self.class_id = class_id
self.label = label
def __repr__(self):
return '<UIMetadata (%s) %r(id=%s)>' % (self.id,
self.class_type, self.class_id)
class Category(db.Model):
__tablename__ = 'category'
id = db.Column(db.Integer, primary_key=True)
name = db.Column(db.String)
description = db.Column(db.String)
order = db.Column(db.Integer)
def __init__(self, name, description, order):
self.name = name
self.description = description
self.order = order
def __repr__(self):
return '<Category %r>' % (self.name)
Category.ui_metadata = db.relationship(UIMetadata,
primaryjoin=and_(Category.id==UIMetadata.class_id,
UIMetadata.class_type=="Category"),
foreign_keys=[UIMetadata.class_id])
Note: the code above is using Flask-SQLAlchemy, hence the db.
prefixes.
On May 10, 12:09 pm, nostradamnit <[email protected]> wrote:
> I'm trying to implement an alternative join relationship pretty much
> exactly like the boston_addresses example in the documentation, but
> I'm running into a 'Could not determine relationship direction...'
> error. I've included the code example. I've tried every possible
> variation I could think of :(
>
> Here's the basic SQL implementation I'm looking to accomplish.
>
> select c.id as cat_id, c.name, ui.label
> from category c join ui_metadata ui
> on c.id = ui.class_id and ui.class_type = 'Category'
>
> Once I figure out how to formulate the relationship, there will be
> other objects like Category that will have similarily related
> ui_metadata.
>
> Thanks in advance for you assistance,
> Sam
>
> The example code (I didn't have an attach option):
>
> from sqlalchemy import create_engine, and_
> from sqlalchemy import Column, Integer, String, MetaData, ForeignKey
> from sqlalchemy.ext.declarative import declarative_base
> from sqlalchemy.orm import sessionmaker, relationship, backref
>
> Base = declarative_base()
> metadata = MetaData()
>
> class Category(Base):
> __tablename__ = 'category'
>
> id = Column(Integer, primary_key=True)
> name = Column(String)
>
> #features = relationship('Feature')
> ui_metadata = relationship('UIMetadata',
> primaryjoin=and_('category.c.id==ui_metadata.c.class_id',
> 'ui_metadata.c.class_type=="Category"'))
>
> def __init__(self, name):
> self.name = name
>
> def __repr__(self):
> return '<Category %r>' % (self.name)
>
> class UIMetadata(Base):
> """ Class to allow UI metadata to be associated with almost any
> other class"""
> __tablename__ = 'ui_metadata'
>
> id = Column(Integer, primary_key=True)
> class_type = Column(String)
> class_id = Column(Integer)
> label = Column(String)
>
> def __init__(self, class_type, class_id, label):
> self.class_type = class_type
> self.class_id = class_id
> self.label = label
>
> def __repr__(self):
> return '<UIMetadata (%s) %r(id=%s)>' % (self.id,
> self.class_type, self.class_id)
>
> def start_session(db_path = None):
> if not db_path:
> db_path = 'test.db'
> engine = create_engine('sqlite:///%s' % db_path, echo=True)
> Session = sessionmaker(bind=engine)
> session = Session()
> Base.metadata.create_all(engine)
>
> return session
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