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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