On Dec 23, 2010, at 10:29 PM, kindly wrote:
> Oh I see.
>
> The issue was that the query was trying to filter on the parent. i.e
>
> query(ManagerInfo).join("manager").filter(Employee.foo == 'bar')
>
> This makes a cross join.
>
> The use case is that this point in the application the ManigerInfo did
> not know what it had joined to. All it knew was that it joined using
> "manager" and Employee was the superclass. This may sound silly on
> this small example.
>
> I already found you can get out the class by finding it in the
> descriptor i.e ManagerInfo.manager.property.mapper.class_, however
> I am not sure how robust that is. It will be fine for now.
sure. In 0.7 it looks like we have ManagerInfo.manager.class_ too.
>
>
> On Dec 24, 1:53 am, Michael Bayer <[email protected]> wrote:
>> On Dec 23, 2010, at 8:38 PM, kindly wrote:
>>
>>
>>
>>> Hello
>>
>>> Is there a nice way to get the subquery object that relates to anon_1
>>> in the below case so you can use it to filter on?
>>
>>> You can get it by q._joinpoint['_joinpoint_entity'] but that is
>>> clearly private.
>>
>>> Thanks
>>
>>> David
>>
>>> class Employee(object): pass
>>
>>> class Manager(Employee): pass
>>
>>> class ManagerInfo(object): pass
>>
>>> employees = Table('employees', metadata,
>>> Column('employee_id', Integer, primary_key=True),
>>> Column('type', String(30), nullable=False)
>>> )
>>
>>> managers = Table('managers', metadata,
>>> Column('employee_id', Integer, ForeignKey('employees.employee_id'),
>>> primary_key=True),
>>> Column('manager_info_id', Integer, ForeignKey('manager_info.id'),
>>> primary_key=True),
>>> )
>>
>>> manager_info = Table('manager_info', metadata,
>>> Column('id', Integer, primary_key=True),
>>> Column('data', String(30), primary_key=True),
>>> )
>>
>>> mapper(Employee, employees, polymorphic_on=employees.c.type, \
>>> polymorphic_identity='employee')
>>
>>> mapper(Manager, managers, inherits=Employee,
>>> polymorphic_identity='engineer')
>>
>>> mapper(ManagerInfo,
>>> manager_info,
>>> properties = dict(manager = orm.relation(Manager))
>>> )
>>
>>> session = Session()
>>
>>> q = session.query(ManagerInfo).join("manager")
>>
>>> print q
>>
>>> """SELECT manager_info.id AS manager_info_id, manager_info.data AS
>>> manager_info_data
>>> FROM manager_info JOIN (SELECT employees.employee_id AS
>>> employees_employee_id, employees.type AS employees_type,
>>> managers.employee_id AS managers_employee_id, managers.manager_info_id
>>> AS managers_manager_info_id
>>> FROM employees JOIN managers ON employees.employee_id =
>>> managers.employee_id) AS anon_1 ON manager_info.id =
>>> anon_1.managers_manager_info_id"""
>>
>> Once you join to ManagerInfo.manager, you'd reference the right joinpoint
>> using the Manager entity itself:
>>
>> query(ManagerInfo).join("manager").filter(Manager.foo == 'bar')
>>
>> That's the reason for the whole joinpoint entity stuff, the Query is keeping
>> track of it, will recognize the usage of "Manager" and will alias all
>> expressions that use it.
>>
>> You can also join to an alias of Manager:
>>
>> malias = aliased(Manager)
>> query(ManagerInfo).join((malias,
>> ManagerInfo.manager)).filter(malias.foo == 'bar')
>>
>> If you need to reference the individual tables that comprise Manager,
>> usually you do that via referencing "managers" and "employees" directly to
>> start with.
>>
>> The joined table inheritance query stuff has taken several years to get
>> right, so if there's something its not doing at that level let me know and I
>> can suggest a workaround or provide a fix.
>
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