you relation should have argument like primary_join= engineers.c.hired_by_id==managers.c.employee_id or similar. i do not know for sure as i've done a layer on top of SA that stores most of this knowledge, so i dont bother with it. Have a look at dbcook.sf.net. u may use it as ORM to build and use your model, or use is just to describe your model then dump the equivalent SA-calls (see usage/example/example*), and use that one, dropping the dbcook. As of joined-inh, SA supports all the 3 single/concrete/joined, but real polymorphism does not work for the concrete case. Also, joined inh is done via left-outer-join which is simpler/faster than an union - although that is also an option. have fun svilen
Dave E wrote: > http://www.sqlalchemy.org/docs/04/mappers.html#advdatamapping_mapper_inheritance_joined > > My question is what if you wanted to add a 'hired' field to say the > employees table & object (from the example in that link) that > references a manager object. In this way I imagine that we are making > another reference to an employee object and might be an issue when > trying to figure out the join. So I'd imagine that the tables look > like: > > employees = Table('employees', metadata, > Column('employee_id', Integer, primary_key=True), > Column('name', String(50)), > Column('type', String(30), nullable=False) > ) > engineers = Table('engineers', metadata, > Column('employee_id', Integer, ForeignKey('employees.employee_id'), > primary_key=True), > Column('hired_by_id',Integer,ForeignKey('managers.employee_id')), > #######INTERESTING PART > Column('engineer_info', String(50)), > ) > managers = Table('managers', metadata, > Column('employee_id', Integer, ForeignKey('employees.employee_id'), > primary_key=True), > Column('manager_data', String(50)), > ) > > and the mappers look like: > > mapper(Employee, employees, polymorphic_on=employees.c.type, > polymorphic_identity='employee') > mapper(Engineer, engineers, inherits=Employee, > polymorphic_identity='engineer', > properties={ > 'hirer':relation(Manager,uselist=False,backref='hired') > }) > mapper(Manager, managers, inherits=Employee, > polymorphic_identity='manager') > > > But the error message you'd get if you do this is: > sqlalchemy.exceptions.ArgumentError: Error determining primary and/or > secondary join for relationship 'Engineer.hirer (Manager)'. If the > underlying error cannot be corrected, you should specify the > 'primaryjoin' (and 'secondaryjoin', if there is an association table > present) keyword arguments to the relation() function (or for > backrefs, by specifying the backref using the backref() function with > keyword arguments) to explicitly specify the join conditions. Nested > error is "Can't determine join between 'Join object on > employees(14680464) and engineers(14680880)' and '_FromGrouping > object'; tables have more than one foreign key constraint relationship > between them. Please specify the 'onclause' of this join explicitly." > > Might I add that this is an extremely informative error message! > > Basically, my question is how do I satisfy this requirement as > described by the error message? I have to make my join more > specific? How would I do that? > > And another question, is Joined Table Inheritance a common thing to do > in SQLAlchemy? > > > --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "sqlalchemy" group. To post to this group, send email to sqlalchemy@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en -~----------~----~----~----~------~----~------~--~---
