You responded! Woot. Thanks. Here's some additional info:
1. __tablename__ is generated automatically based on the class name.
Flask-SQLAlchemy does this for us. The __tablename__ for AutocreatedGroup
and TopicAutocreatedGroup model is both "autocreated_group".
2. Sorry, I might have included too much code in my snippet. Group extends
Community through joined table inheritance (primary key with foreign key to
community). AutocreatedGroup extends Group in the same manner. The
relationship of interest is between AutocreatedGroup and
TopicAutocreatedGroup. TopicAutocreatedGroup does appear to inherit through
a single table.
3. Yeah, I'm redefining polymorphic_on for Group since it depends on a
boolean switch. I'm doing the same for AutocreatedGroup since it depends on
the name of the class.
AutocreatedGroup and TopicAutocreatedGroup do appear to have all of the
same columns of Group and Community. The AutocreatedGroup table does have
the topic_created_from_id column, but that same column doesn't appear in
the mapper.
Thanks, again. I'm definitely not a SQL Alchemy expert, so your help is
appreciated greatly.
On Wednesday, August 15, 2012 11:21:41 AM UTC-4, Michael Bayer wrote:
>
>
> On Aug 15, 2012, at 10:45 AM, Kuba Dolecki wrote:
>
> Hi,
>
> We've used joined table inheritance up to this point, but performance
> issues are making us explore single table inheritance. I'm running into a
> problem with mapper configuration. Using SQLAlchemy 0.7.8, Flask-SQLAlchemy
> 0.16, and Flask 0.8. Here is the inheritance:
>
>
> there are many things that are confusing about this model.
>
> 1. I don't see any mention of __tablename__ anywhere. Where is the table
> defined ?
>
> 2. You say this is single table inheritance, but I see each subclass has
> it's own primary key column, with a foreign key column pointing back to the
> superclass "table" (which isn't present). This doesn't fit with single
> table inheritance at all.
>
> 3. There's a second re-definition of "polymorphic_on". This isn't
> necessarily a mistake, as it is supported that loading a specific
> sub-hierarchy may have a different system of determining polymorphic
> identity - usually this applies to concrete schemes. But with joined or
> single table inheritance it's extremely unusual, as the base table is what
> determines object identity in both of these cases. If you load a
> collection of "community" rows, the ORM needs to decide from that base
> table alone what the subclass should be. It won't see a
> sub-polymorphic-on unless the original query was against that subclass.
>
>
> class Community(BaseModel, db.Model):
> # Bar
>
> class Group(Community):
> ###
> Group utilized joined table inheritance to extend Community
> ###
> id = db.Column(db.Integer, db.ForeignKey('community.id'),
> primary_key=True, nullable=False)
> autocreated = db.Column(db.Boolean, nullable=False, default=False)
>
> @declared_attr
> def __mapper_args__(cls):
> name = cls._name()
> identity = {
> 'polymorphic_on': case([
> (cls.autocreated == True, "autocreated_group"),
> (cls.autocreated == False, "group")
> ]),
> 'polymorphic_identity': name
> }
> return identity
>
> class AutocreatedGroup(Group):
> ###
> AutocreatedGroup extends Group through joined table inheritance
> ###
> id = db.Column(db.Integer, db.ForeignKey('group.id'),
> primary_key=True, \
> nullable=False)
>
> @declared_attr
> def __mapper_args__(cls):
> name = cls._name()
> identity = {
> 'polymorphic_on': cls.autocreated_type,
> 'polymorphic_identity': name
> }
> return identity
>
> class TopicAutocreatedGroup(AutocreatedGroup):
> ###
> TopicAutocreatedGroup extends AutocreatedGroup through single
> table inheritance
> ###
> @declared_attr
> def __mapper_args__(cls):
> return {'polymorphic_identity': cls._name()}
>
> topic_created_from_id = db.Column(
> db.Integer,
> db.ForeignKey('topic.id'),
> nullable = True
> )
> topic_created_from = db.relation(
> "Topic",
> primaryjoin="Topic.id ==
> TopicAutocreatedGroup.topic_created_from_id",
> backref=db.backref("topic_groups", uselist=True),
> uselist=False, lazy='subquery'
> )
>
> Here is the stacktrace:
> Traceback (most recent call last):
> File "/srv/.env/lib/python2.6/site-packages/flask/app.py", line 1518, in
> __call__
> return self.wsgi_app(environ, start_response)
> File "/srv/.env/lib/python2.6/site-packages/flask/app.py", line 1506, in
> wsgi_app
> response = self.make_response(self.handle_exception(e))
> File "/srv/.env/lib/python2.6/site-packages/flask/app.py", line 1504, in
> wsgi_app
> response = self.full_dispatch_request()
> File "/srv/.env/lib/python2.6/site-packages/flask/app.py", line 1264, in
> full_dispatch_request
> rv = self.handle_user_exception(e)
> File "/srv/.env/lib/python2.6/site-packages/flask/app.py", line 1260, in
> full_dispatch_request
> rv = self.preprocess_request()
> File "/srv/.env/lib/python2.6/site-packages/flask/app.py", line 1387, in
> preprocess_request
> rv = func()
> File "/srv/franklin-api/api/helpers/login_manager.py", line 53, in
> _load_user
> user = User.for_auth_token(token)
> File "/srv/franklin-api/api/models/user.py", line 584, in for_auth_token
> user_for_token = cls.query.filter(cls.auth_token == auth_token).first()
> File "/srv/.env/lib/python2.6/site-packages/flask_sqlalchemy.py", line
> 394, in __get__
> mapper = orm.class_mapper(type)
> File "/srv/.env/lib/python2.6/site-packages/sqlalchemy/orm/util.py",
> line 660, in class_mapper
> mapperlib.configure_mappers()
> File "/srv/.env/lib/python2.6/site-packages/sqlalchemy/orm/mapper.py",
> line 2255, in configure_mappers
> raise e
> InvalidRequestError: One or more mappers failed to initialize - can't
> proceed with initialization of other mappers. Original exception was:
> Class <class 'api.models.autocreated_group.TopicAutocreatedGroup'> does not
> have a mapped column named 'topic_created_from_id'
>
>
> It appears the Columns inside classes that inherit through single table
> inheritance are not included in the mapper. Any idea of what may be going
> wrong?
>
> Thank you,
> Kuba
>
> P.S. What should __mapper_args__ look like for AutocreatedGroup? Should
> "topic_created_from_id" be automatically included in the
> "excluded_properties" value? Currently, it's empty if I print it out.
>
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